Efficacy and safety of regenerated cellulose topical gauze haemostats in managing secondary haemostasis: a randomised control trial.

OBJECTIVE: To compare the efficacy and safety of HemoStyp (United Health Products, US), a neutralised oxidised regenerated cellulose (NORC) and Surgicel (Johnson & Johnson, US), an oxidised regenerated cellulose (ORC), in the management of bleeding of surgical wounds during abdominal, thoracic and vascular surgeries. METHOD: This study was a prospective, non-inferiority, multicentre, randomised, open-label trial. Surgical procedures were performed according to expected standard of care and in compliance with all relevant laws and institutional guidelines. Patients who developed Lewis Bleeding Scale grade 1 and grade 2 bleeds not controlled through conventional techniques were randomised to either the NORC or ORC treatment arms. Bleeding was measured every 30 seconds after treatment, ending at five minutes after haemostasis was achieved or at 10 minutes if haemostasis was not achieved. RESULTS: A total of 236 patients were included in the study. There was a total of seven adverse events in the study, none of which had causality related to either the NORC or ORC. For all surgical procedures, haemostasis was achieved more quickly with the NORC than the ORC (p<0.0001). In addition, haemostasis for all patients was achieved in under two minutes for the NORC compared with 81% of patients in the ORC groups. For Lewis Bleeding Scale grade 1 bleeds, the median time to control bleeding was 24 seconds in the NORC group and 51 seconds for the ORC group. For grade 2 bleeds, time to control bleeding was 76 seconds and 116 seconds, respectively. CONCLUSION: For patients in this study, haemostasis was achieved more quickly in the NORC treatment group compared with the ORC group, in patients with Lewis grade 1 or 2 bleeds caused by surgical wounds generated during abdominal, thoracic and vascular surgeries.

Transcatheter aspiration of large pacemaker and implantable cardioverter-defibrillator lead vegetations facilitating safe transvenous lead extraction.

AIMS: Treatment of patients with systemic cardiac implantable electronic device (CIED) infection with large lead vegetations is challenging and associated with relevant morbidity and mortality. To avoid complications from open surgical extraction, a novel approach with percutaneous aspiration of large vegetations prior to transvenous lead extraction was instituted. The results of this treatment concept were retrospectively analysed in this multicentre study. METHODS AND RESULTS: One hundred and one patients [mean age 68.2 ± 13.1 (30-92) years] were treated in four centres for endovascular CIED infection with large lead vegetations. Mean lead vegetation size was 30.7 ± 13.5 mm. Two hundred and forty-seven leads were targeted for extraction (170 pacemaker leads, 77 implantable cardioverter-defibrillator leads). Mean lead implant duration was 81.7 (1-254) months. The transcatheter aspiration system with a specialized long venous drainage cannula and a funnel-shaped tip was based on a veno-venous extracorporeal circuit with an in-line filter. The aspiration of vegetations showed complete procedural success in 94.0% (n = 95), partial success in 5.0% (n = 5). Three major complications (3.0%) were encountered. Complete procedural success (per lead) of the subsequently performed transvenous lead extraction procedure was 99.2% (n = 245). Thirty-day mortality was 3.0% (n = 3). Five patients (5.0%) died in the further course on Days 51, 54, 68, 134, and 182 post-procedure (septic complications: n = 4; heart failure: n = 1). CONCLUSION: The percutaneous aspiration procedure is highly effective and is associated with a low complication profile. The aspiration of vegetations immediately prior and during the lead extraction procedure may avoid septic embolization into the pulmonary circulation. This may potentially lead to a long-term survival benefit.

Structural Identification and Kinetic Analysis of the in Vitro Products Formed by Reaction of Bisphenol A-3,4-quinone with N-Acetylcysteine and Glutathione.

Bisphenol A (BPA) has received considerable attention as an endocrine disrupting chemical and a possible substrate for genotoxic metabolites. BPA metabolism leads to formation of electrophilic o-quinones cable of binding to DNA and other endogenous nucleophiles. We have structurally identified the products resulting from the reaction of bisphenol A-3,4-quinone (BPAQ) with N-acetylcysteine (NAC) and glutathione (GSH). The major and minor isomers are both the result of 1,6-conjugate addition and are produced almost instantly in high yield. Reactions using 1.3 equiv of GSH showed the presence of a bis-glutathionyl adduct which was not observed using higher GSH concentration relative to BPAQ. NAC reactions with BPAQ showed no bis-N-acetylcysteinyl adducts. Stopped-flow kinetic analysis reveals the 1,6-conjugate additions to be reversible with a forward free energy of activation of 9.2 and 7.8 kcal/mol for the NAC and GSH reactions, respectively. The bimolecular forward rate constant at 19.4 °C was approximately three time faster for GSH compared to NAC, 1547 vs 496 M-1 s-1. The free energy of activation for the reverse reactions were similar, 11.7 and 11.2 kcal/mol for NAC and GSH, respectively. We plan to use this model system to further explore the mechanism of adduct formation between sulfur nucleophiles and o-quinones and the resulting chemical properties of both NAC and GSH adducts.

Percutaneous Vacuum-Assisted Thrombectomy Device Used for Removal of Large Vegetations on Infected Pacemaker and Defibrillator Leads as an Adjunct to Lead Extraction.

This case series reports our early experience with a minimally invasive percutaneous method of safely removing large vegetations during lead extraction in septic cardiac implantable electronic devices (CIED). Debate exists concerning the management of vegetations involving these devices. Lead extraction is mandated for infections, but vegetations may embolize, causing complications. Surgical debridement is recommended; alternatives include cardiopulmonary bypass, minimally invasive thoracotomy, or transatrial approaches. The AngioVac device allows percutaneous right heart bypass and suction removal of vegetations under echocardiographic and fluoroscopic guidance. This case series describes our first 20 patients, all critically ill with persistent sepsis and vegetations despite long-term antibiotics. This series includes patients who would not have been eligible for alternative procedures due to contraindications and highlights the potential role of this new technology.

Detection of intermediates in the oxidative half-reaction of the FAD-dependent thymidylate synthase from Thermotoga maritima: carbon transfer without covalent pyrimidine activation.

Thymidylate, a vital DNA precursor, is synthesized by thymidylate synthases (TSs). A second class of TSs, encoded by the thyX gene, is found in bacteria and a few other microbes and is especially widespread in anaerobes. TS encoded by thyX requires a flavin adenine dinucleotide prosthetic group for activity. In the oxidative half-reaction, the reduced flavin is oxidized by 2'-deoxyuridine 5'-monophosphate (dUMP) and (6R)-N5,N10-methylene-5,6,7,8-tetrahydrofolate (CH2THF), synthesizing 2'-deoxythymidine 5'-monophosphate (dTMP). dTMP synthesis is a complex process, requiring the enzyme to promote carbon transfer, probably by increasing the nucleophilicity of dUMP and the electrophilicity of CH2THF, and reduction of the transferred carbon. The mechanism of the oxidative half-reaction was investigated by transient kinetics. Two intermediates were detected, the first by a change in the flavin absorbance spectrum in stopped-flow experiments and the second by the transient disappearance of deoxynucleotide in acid quenching experiments. The effects of substrate analogues and the behavior of mutated enzymes on these reactions lead to the conclusion that activation of dUMP does not occur through a Michael-like addition, the mechanism for the activation analogous with that of the flavin-independent TS. Rather, we propose that the nucleophilicity of dUMP is enhanced by electrostatic polarization upon binding to the active site. This conclusion rationalizes many of our observations, for instance, the markedly slower reactions when two arginine residues that hydrogen bond with the uracil moiety of dUMP were mutated to alanine. The activation of dUMP by polarization is consistent with the majority of the published data on ThyX and provides a testable mechanistic hypothesis.

Shewanella oneidensis cytochrome c nitrite reductase (ccNiR) does not disproportionate hydroxylamine to ammonia and nitrite, despite a strongly favorable driving force.

Cytochrome c nitrite reductase (ccNiR) from Shewanella oneidensis, which catalyzes the six-electron reduction of nitrite to ammonia in vivo, was shown to oxidize hydroxylamine in the presence of large quantities of this substrate, yielding nitrite as the sole free nitrogenous product. UV-visible stopped-flow and rapid-freeze-quench electron paramagnetic resonance data, along with product analysis, showed that the equilibrium between hydroxylamine and nitrite is fairly rapidly established in the presence of high initial concentrations of hydroxylamine, despite said equilibrium lying far to the left. By contrast, reduction of hydroxylamine to ammonia did not occur, even though disproportionation of hydroxylamine to yield both nitrite and ammonia is strongly thermodynamically favored. This suggests a kinetic barrier to the ccNiR-catalyzed reduction of hydroxylamine to ammonia. A mechanism for hydroxylamine reduction is proposed in which the hydroxide group is first protonated and released as water, leaving what is formally an NH2(+) moiety bound at the heme active site. This species could be a metastable intermediate or a transition state but in either case would exist only if it were stabilized by the donation of electrons from the ccNiR heme pool into the empty nitrogen p orbital. In this scenario, ccNiR does not catalyze disproportionation because the electron-donating hydroxylamine does not poise the enzyme at a sufficiently low potential to stabilize the putative dehydrated hydroxylamine; presumably, a stronger reductant is required for this.

Intermediate partitioning kinetic isotope effects for the NIH shift of 4-hydroxyphenylpyruvate dioxygenase and the hydroxylation reaction of hydroxymandelate synthase reveal mechanistic complexity.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) and hydroxymandelate synthase (HMS) are similar enzymes that catalyze complex dioxygenation reactions using the substrates 4-hydroxyphenylpyruvate (HPP) and dioxygen. Both enzymes decarboxylate HPP and then hydroxylate the resulting hydroxyphenylacetate (HPA). The hydroxylation reaction catalyzed by HPPD displaces the aceto substituent of HPA in a 1,2-shift to form 2,5-dihydroxyphenylacetate (homogentisate, HG), whereas the hydroxylation reaction of HMS places a hydroxyl on the benzylic carbon forming 3'-hydroxyphenylacetate (S-hydroxymandelate, HMA) without ensuing chemistry. The wild-type form of HPPD and variants of both enzymes uncouple to form both native and non-native products. We have used intermediate partitioning to probe bifurcating steps that form these products by substituting deuteriums for protiums at the benzylic position of the HPP substrate. These substitutions result in altered ratios of products that can be used to calculate kinetic isotope effects (KIE) for the formation of a specific product. For HPPD, secondary normal KIEs indicate that cleavage of the bond in the displacement reaction prior to the shift occurs by a homolytic mechanism. NMR analysis of HG derived from HPPD reacting with enantiomerically pure R-3'-deutero-HPP indicates that no rotation about the bond to the radical occurs, suggesting that collapse of the biradical intermediate is rapid. The production of HMA was observed in HMS and HPPD variant reactions. HMS hydroxylates to form exclusively S-hydroxymandelate. When HMS is reacted with R-3'-deutero-HPP, the observed kinetic isotope effect represents geometry changes in the initial transition state for the nonabstracted proton. These data show evidence of sp(3) hybridization in a HPPD variant and sp(2) hybridization in HMS variants, suggesting that HMS stabilizes a more advanced transition state in order to catalyze H-atom abstraction.

Trapping of an intermediate in the reaction catalyzed by flavin-dependent thymidylate synthase.

Thymidylate is a DNA nucleotide that is essential to all organisms and is synthesized by the enzyme thymidylate synthase (TSase). Several human pathogens rely on an alternative flavin-dependent thymidylate synthase (FDTS), which differs from the human TSase both in structure and molecular mechanism. It has recently been shown that FDTS catalysis does not rely on an enzymatic nucleophile and that the proposed reaction intermediates are not covalently bound to the enzyme during catalysis, an important distinction from the human TSase. Here we report the chemical trapping, isolation, and identification of a derivative of such an intermediate in the FDTS-catalyzed reaction. The chemically modified reaction intermediate is consistent with currently proposed FDTS mechanisms that do not involve an enzymatic nucleophile, and it has never been observed during any other TSase reaction. These findings establish the timing of the methylene transfer during FDTS catalysis. The presented methodology provides an important experimental tool for further studies of FDTS, which may assist efforts directed toward the rational design of inhibitors as leads for future antibiotics.

Evidence for the mechanism of hydroxylation by 4-hydroxyphenylpyruvate dioxygenase and hydroxymandelate synthase from intermediate partitioning in active site variants.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) and hydroxymandelate synthase (HMS) each catalyze similar complex dioxygenation reactions using the substrates 4-hydroxyphenylpyruvate (HPP) and dioxygen. The reactions differ in that HPPD hydroxylates at the ring C1 and HMS at the benzylic position. The HPPD reaction is more complex in that hydroxylation at C1 instigates a 1,2-shift of an aceto substituent. Despite that multiple intermediates have been observed to accumulate in single turnover reactions of both enzymes, neither enzyme exhibits significant accumulation of the hydroxylating intermediate. In this study we employ a product analysis method based on the extents of intermediate partitioning with HPP deuterium substitutions to measure the kinetic isotope effects for hydroxylation. These data suggest that, when forming the native product homogentisate, the wild-type form of HPPD produces a ring epoxide as the immediate product of hydroxylation but that the variant HPPDs tended to also show the intermediacy of a benzylic cation for this step. Similarly, the kinetic isotope effects for the other major product observed, quinolacetic acid, showed that either pathway is possible. HMS variants show small normal kinetic isotope effects that indicate displacement of the deuteron in the hydroxylation step. The relatively small magnitude of this value argues best for a hydrogen atom abstraction/rebound mechanism. These data are the first definitive evidence for the nature of the hydroxylation reactions of HPPD and HMS.

Kinetic mechanism of human DNA ligase I reveals magnesium-dependent changes in the rate-limiting step that compromise ligation efficiency.

DNA ligase I (LIG1) catalyzes the ligation of single-strand breaks to complete DNA replication and repair. The energy of ATP is used to form a new phosphodiester bond in DNA via a reaction mechanism that involves three distinct chemical steps: enzyme adenylylation, adenylyl transfer to DNA, and nick sealing. We used steady state and pre-steady state kinetics to characterize the minimal mechanism for DNA ligation catalyzed by human LIG1. The ATP dependence of the reaction indicates that LIG1 requires multiple Mg(2+) ions for catalysis and that an essential Mg(2+) ion binds more tightly to ATP than to the enzyme. Further dissection of the magnesium ion dependence of individual reaction steps revealed that the affinity for Mg(2+) changes along the reaction coordinate. At saturating concentrations of ATP and Mg(2+) ions, the three chemical steps occur at similar rates, and the efficiency of ligation is high. However, under conditions of limiting Mg(2+), the nick-sealing step becomes rate-limiting, and the adenylylated DNA intermediate is prematurely released into solution. Subsequent adenylylation of enzyme prevents rebinding to the adenylylated DNA intermediate comprising an Achilles' heel of LIG1. These ligase-generated 5'-adenylylated nicks constitute persistent breaks that are a threat to genomic stability if they are not repaired. The kinetic and thermodynamic framework that we have determined for LIG1 provides a starting point for understanding the mechanism and specificity of mammalian DNA ligases.

The rate-limiting catalytic steps of hydroxymandelate synthase from Amycolatopsis orientalis.

Hydroxymandelate synthase (HMS) catalyzes the committed step in the formation of p-hydroxyphenylglycine, a recurrent substructure of polycyclic nonribosomal peptide antibiotics such as vancomycin. HMS has the same structural fold as and uses the same substrates as 4-hydroxyphenylpyruvate dioxygenase (HPPD) (4-hydroxyphenylpyruvate (HPP) and O(2)). Moreover, HMS catalyzes a very similar dioxygenation reaction to that of HPPD, adding the second oxygen atom to the benzylic position, rather than the aromatic C1 carbon of the substrate. The dissociation constant for HPP (59 microM) was measured under anaerobic conditions by titrating substrate with enzyme and monitoring the intensity of the weak (epsilon(475nm ) approximately 250 M(-1) cm(-1)) charge-transfer absorption band of the HMS.Fe(II).HPP complex. Pre-steady-state analysis indicates that evidence exists for the accumulation of three intermediates in a single turnover and the decay of the third is rate-limiting in multiple turnovers. The rate constants used to fit the data were k(1) = 1 x 10(5) M(-1) s(-1), k(2) = 250 s(-1), k(3) = 5 s(-1), and k(4) = 0.3 s(-1). However, the values for k(1) and k(2) could not be accurately measured due to both a prolonged mixing time for the HMS system that obscures observation at the early times (<10 ms) and the apparent high relative value of k(2). The third phase, k(3), is attributed to the formation of the product complex, and no kinetic isotope effect was observed on this step when the protons of the substrate's benzylic carbon were substituted with deuteriums, suggesting that hydroxylation is fast relative to the steps observed. The final and predominantly rate-limiting step shows a 3-fold decrease in the magnitude of the rate constant in deuterium oxide solvent, and a proton inventory for this step suggests the contribution of a single proton from the solvent environment.

An unusual mechanism of thymidylate biosynthesis in organisms containing the thyX gene.

Biosynthesis of the DNA base thymine depends on activity of the enzyme thymidylate synthase to catalyse the methylation of the uracil moiety of 2'-deoxyuridine-5'-monophosphate. All known thymidylate synthases rely on an active site residue of the enzyme to activate 2'-deoxyuridine-5'-monophosphate. This functionality has been demonstrated for classical thymidylate synthases, including human thymidylate synthase, and is instrumental in mechanism-based inhibition of these enzymes. Here we report an example of thymidylate biosynthesis that occurs without an enzymatic nucleophile. This unusual biosynthetic pathway occurs in organisms containing the thyX gene, which codes for a flavin-dependent thymidylate synthase (FDTS), and is present in several human pathogens. Our findings indicate that the putative active site nucleophile is not required for FDTS catalysis, and no alternative nucleophilic residues capable of serving this function can be identified. Instead, our findings suggest that a hydride equivalent (that is, a proton and two electrons) is transferred from the reduced flavin cofactor directly to the uracil ring, followed by an isomerization of the intermediate to form the product, 2'-deoxythymidine-5'-monophosphate. These observations indicate a very different chemical cascade than that of classical thymidylate synthases or any other known biological methylation. The findings and chemical mechanism proposed here, together with available structural data, suggest that selective inhibition of FDTSs, with little effect on human thymine biosynthesis, should be feasible. Because several human pathogens depend on FDTS for DNA biosynthesis, its unique mechanism makes it an attractive target for antibiotic drugs.

Arginine deiminase has multiple regulatory roles in the biology of Giardia lamblia.

The protozoan parasite Giardia lamblia uses arginine deiminase (ADI) to produce energy from free L-arginine under anaerobic conditions. In this work, we demonstrate that, in addition to its known role as a metabolic enzyme, it also functions as a peptidylarginine deiminase, converting protein-bound arginine into citrulline. G. lamblia ADI specifically binds to and citrullinates the arginine in the conserved CRGKA tail of variant-specific surface proteins (VSPs), affecting both antigenic switching and antibody-mediated cell death. During encystation, ADI translocates from the cytoplasm to the nuclei and appears to play a regulatory role in the expression of encystation-specific genes. ADI is also sumoylated, which might modulate its activity. Our findings reveal a dual role played by ADI and define novel regulatory pathways used by Giardia for survival.

The Interaction of Hydroxymandelate Synthase with the 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor: NTBC.

Hydroxymandelate synthase (HMS) catalyzes the committed step in the formation of para-hydroxyphenylglycine, a recurrent substructure of polycyclic non-ribosomal peptide antibiotics such as vancomycin. HMS uses the same substrates as 4-hydroxyphenylpyruvate dioxygenase (HPPD), 4-hydroxyphenylpyruvate (HPP) and O(2), and also conducts a dioxygenation reaction. The difference between the two lies in the insertion of the second oxygen atom, HMS directing this atom onto the benzylic carbon of the substrate while HPPD hydroxylates the aromatic C1 carbon. We have shown that HMS will bind NTBC, a herbicide/therapeutic whose mode of action is based on the inhibition of HPPD. This occurs despite the difference in residues at the active site of HMS from those known to contact the inhibitor in HPPD. Moreover, the minimal kinetic mechanism for association of NTBC to HMS differs only slightly from that observed with HPPD. The primary difference is that three charge-transfer species are observed to accumulate during association. The first reversible complex forms with a weak dissociation constant of 520 microM, the subsequent two charge-transfer complexes form with rate constants of 2.7 s(-1) and 0.67 s(-1). As was the case for HPPD, the final complex has the most intense charge-transfer, is not observed to dissociate, and is unreactive towards dioxygen.

Significance of pleural effusion in neuroblastoma.

BACKGROUND: Pleural effusion is uncommon at diagnosis of neuroblastoma in children. Because the presence of malignant cells in pleural fluid may significantly change the management and outcome of patients with neuroblastoma, we retrospectively analyzed a cohort of neuroblastoma patients who presented with pleural effusion at the time of diagnosis to determine the incidence, presentation, stage, treatment, and outcome of these patients. METHODS: We reviewed the presenting features of 295 patients with the diagnosis of neuroblastoma who received treatment at St. Jude Children's Research Hospital between 1991 and 2005. Patients were chosen for further analysis if pleural effusion had been identified on chest radiographs or computed tomography (CT) scans at diagnosis RESULTS: Thirty-one out of 295(10.5%) patients with neuroblastoma had pleural effusion identified at time of presentation. International neuroblastoma staging system (INSS) risk stratification was high risk in 29 cases and intermediate risk and low risk in 1 case each. The primary site of disease was abdomen in 26 patients; mediastinum in 5. We conducted cytologic analysis of pleural fluid of nine patients; the specimen of seven contained malignant cells. Eighteen of 31 patients died of progressive or recurrent disease. CONCLUSION: In patients with neuroblastoma, pleural effusion is usually associated with unfavorable biologic features and high-risk disease. Pleural fluid should be examined cytologically and at a time when the results would change the risk stratification. There was no statistically significant difference in the survival rate of the patients with high-risk neuroblastoma with or without malignant pleural effusion.

Three-dimensional imaging improves surgical performance for both novice and experienced operators using the da Vinci Robot System.

BACKGROUND: This study was designed to evaluate the impact of 3-dimensional vision on the performance of resident and experienced surgeons using the da Vinci Robot System (Intuitive Surgical, Sunnyvale, CA). METHODS: Four tasks were performed by 12 surgeons with varying experience. Performance times and errors were recorded using both 2-dimensional and 3-dimensional vision for each task. RESULTS: Performance time and error rates for all 4 skills confirm a significant advantage using 3-dimensional vision. Performance times were reduced by 34% to 46% using 3-dimensional imaging for all participants with statistical significance. Error rates were reduced by 44% and 66%. CONCLUSION: Independent of the biomechanical advantages of the da Vinci Robot System, 3-dimensional vision allows for significant improvement in performance times and error rates for both inexperienced residents and advanced laparoscopic surgeons.

Epigenetic mechanisms are involved in the control of Giardia lamblia antigenic variation.

Giardia lamblia, an intestinal dwelling protozoan parasite, undergoes surface antigenic variation where only one of an estimated 150 variant-specific surface proteins (VSPs) is expressed and present on the surface at any one time. Transcriptional switching between VSPs results in replacement of one VSP by another. The mechanisms that control antigenic variation are poorly understood and difficult to study because there are multiple copies of each VSP and strong similarity with other VSPs. In order to study transcriptional regulation of one specific vsp, a haemagglutinin (HA) epitope-tagged h7 was integrated into the G. lamblia GS genome. We show that HA-tagged H7 undergoes antigenic variation in the same manner as native H7, also present in the GS genome. Control of expression of both HA-tagged H7 and native H7 is independent of each other even though the genes and their surrounding 5' and 3' flanking sequences are virtually identical. Analysis of expressing and non-expressing clones revealed an absence of HA-tagged h7 gene rearrangements upon switching and acetylation of histone lysine residues within the 167 nucleotides 5' to the expressed HA-tagged h7 gene. Lack of vsp rearrangements and acetylation of expressed immediate upstream regions implicates involvement of epigenetic mechanisms in antigenic variation.

A novel palmitoyl acyl transferase controls surface protein palmitoylation and cytotoxicity in Giardia lamblia.

The intestinal protozoan parasite Giardia lamblia undergoes surface antigenic variation whereby one of a family of structurally related variant-specific surface proteins (VSPs) is replaced in a regulated process by another antigenically distinct VSP. All VSPs are type I membrane proteins that have a conserved hydrophobic sequence terminated by the invariant hydrophilic amino acids, CRGKA. Using transfected Giardia constitutively expressing HA-tagged VSPH7 and incubated with radioactive [3H]palmitate, we demonstrate that the palmitate is attached to the Cys in the conserved CRGKA tail. Surface location of mutant VSPs lacking either the CRGKA tail or its Cys is identical to that of wild-type VSPH7 but non-palmitoylated mutants fail to undergo complement-independent antibody specific cytotoxicity. In addition, membrane localization of non-palmitoylated mutant VSPH7 changes from a pattern similar to rafts to non-rafts. Palmitoyl transferases (PAT), responsible for protein palmitoylation in other organisms, often possess a cysteine-rich domain containing a conserved DHHC motif (DHHC-CRD). An open reading frame corresponding to a putative 50 kDa Giardia PAT (gPAT) containing a DHHC-CRD motif was found in the Giardia genome database. Expression of epitope-tagged gPAT using a tetracycline inducible vector localized gPAT to the plasma membrane, a pattern similar to that of VSPs. Transfection with gPAT antisense producing vectors inhibits gPAT expression and palmitoylation of VSPs in vitro confirming the function of gPAT. These results show that VSPs are palmitoylated at the cysteine within the conserved tail by gPAT and indicate an essential function of palmitoylation in control of VSP-mediated signalling and processing.

The activity of a developmentally regulated cysteine proteinase is required for cyst wall formation in the primitive eukaryote Giardia lamblia.

Giardia is an intestinal parasite that belongs to the earliest diverging branch of the eukaryotic lineage of descent. Giardia undergoes adaptation for survival outside the host's intestine by differentiating into infective cysts. Encystation involves the synthesis and transport of cyst wall constituents to the plasma membrane for release and extracellular organization. Nevertheless, little is known about the molecular events related to cyst wall biogenesis in Giardia. Among the components of the cyst wall there are two proteins that we have previously identified and characterized: CWP1 (26 kDa) and CWP2 (39 kDa). Expression of these proteins is coordinately induced, and both concentrated within encystation-specific secretory vesicles before their extracellular polymerization. Although highly similar to each other at the amino terminus, CWP2 includes a COOH-terminal 121-amino acid extension. Here, we show that this extension, rich in basic residues, is cleaved from CWP2 before cyst wall formation by an intracellular cysteine proteinase activity, which is induced during encystation like CWPs. Specific inhibitors prevent release of cyst wall materials, abolishing cyst wall formation. We also report the purification, cloning, and characterization of the encystation-specific cysteine proteinase responsible for the proteolytic processing of CWP2, which is homologue to lysosomal cathepsin C. Encystation-specific cysteine proteinase ESCP possesses unique characteristics compared with cathepsins from higher eukaryotes, such as a transmembrane domain and a short cytoplasmic tail. These features make this enzyme the most divergent cathepsin C identified to date and provide new insights regarding cyst wall formation in Giardia.