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1.
BMJ Open ; 14(3): e084412, 2024 Mar 23.
Article in English | MEDLINE | ID: mdl-38521521

ABSTRACT

INTRODUCTION: Androgen deprivation therapy (ADT) is commonly used to treat men with locally advanced or metastatic prostate cancer. Men receiving ADT experience numerous side effects and frequently report unmet supportive care needs. An essential part of quality cancer care is survivorship care. To date, an optimal effective approach to survivorship care for men with prostate cancer on ADT has not been described. This protocol describes a randomised trial of tele-based nurse-led survivorship that addresses this knowledge gap: (1) determine the effectiveness of a nurse-led survivorship care intervention (PCEssentials), relative to usual care, for improving health-related quality of life (HR-QoL) in men with prostate cancer undergoing ADT and (2) evaluate PCEssentials implementation strategies and outcomes, including cost-effectiveness, compared with usual care. METHODS AND ANALYSIS: This is an effectiveness-implementation hybrid (type 1) trial with participants randomised to one of two arms: (1) minimally enhanced usual care and (2) nurse-led prostate cancer survivorship essentials (PCEssentials) delivered over four tele-based sessions, with a booster session 5 months after session 1. Eligible participants are Australian men with prostate cancer commencing ADT and expected to be on ADT for a minimum of 12 months. Participants are followed up at 3, 6 and 12 months postrecruitment. Primary outcomes are HR-QoL and self-efficacy. Secondary outcomes are psychological distress, insomnia, fatigue and physical activity. A concurrent process evaluation with participants and study stakeholders will be undertaken to determine effectiveness of delivery of PCEssentials. ETHICS AND DISSEMINATION: Ethics approval was obtained from the Metro South Health HREC (HREC/2021/QMS/79429). All participants are required to provide written informed consent. Outcomes of this trial will be published in peer-reviewed journals. The findings will be presented at conferences and meetings, local hospital departments, participating organisations/clinical services, and university seminars, and communicated at community and consumer-led forums. TRIAL REGISTRATION NUMBER: ACTRN12622000025730.


Subject(s)
Cancer Survivors , Prostatic Neoplasms , Male , Humans , Prostatic Neoplasms/drug therapy , Prostatic Neoplasms/psychology , Quality of Life/psychology , Androgen Antagonists/therapeutic use , Androgens , Prostate , Survivorship , Nurse's Role , Australia , Randomized Controlled Trials as Topic
2.
J Robot Surg ; 18(1): 61, 2024 Feb 03.
Article in English | MEDLINE | ID: mdl-38308726

ABSTRACT

The incidence of incisional hernia (IH) following robotic-assisted laparoscopic prostatectomy (RALP) varies widely within the literature (0.4-9.7%). Whilst small hernias may go unnoticed, the potential exists for bowel strangulation and subsequent emergency surgery. We suggest that the extraction site may influence the rate of IH. A retrospective chart review of a single surgeon RALP series was undertaken. One hundred charts were sampled, of which 69 had sufficient data to be analysed. Prior to July 2017, specimen extraction had been via the supra-umbilical port site. After this time, specimens were extracted via a Pfannenstiel incision. Of the 69 patients, 24 underwent RALP prior to July 2017. Three patients developed IH at the supra-umbilical port extended for extraction site in the pre-2017 group and three patients developed IH at the supra-umbilical port (not extraction) site in the post-2017 group. The rate of IH was almost double in the pre-July 2017 group (12.5% vs. 6.7%). No patient developed an incisional hernia at the Pfannenstiel site in the post-2017 group. In our series, no patient developed a hernia at the Pfannenstiel site. This is in keeping with the reported < 1% IH rate following Pfannenstiel specimen extraction. Given that incisional hernias are a known complication of robotic surgery, thought should be given to changing the site of specimen extraction site to lower the rate of incisional hernias and the morbidity associated with such.


Subject(s)
Incisional Hernia , Laparoscopy , Robotic Surgical Procedures , Male , Humans , Incisional Hernia/epidemiology , Incisional Hernia/etiology , Robotic Surgical Procedures/methods , Retrospective Studies , Laparoscopy/adverse effects , Prostatectomy/adverse effects
3.
Urol Oncol ; 41(2): 105.e9-105.e18, 2023 02.
Article in English | MEDLINE | ID: mdl-36437157

ABSTRACT

BACKGROUND AND OBJECTIVE: Radical prostatectomy (RP) is a common and widely used treatment for localized prostate cancer. Sequela following RP may include urinary incontinence and sexual dysfunction, outcomes which are recorded within a bi-national Prostate Cancer Outcomes Registry. The objective was to report population-wide urinary incontinence and sexual function outcomes recorded at 12 months following RP; and to quantify and explore factors associated with variation in outcome. MATERIALS AND METHODS: The Prostate Cancer Outcomes Registry of Australia and New Zealand (PCOR-ANZ) was used for this study. Participants were treated with radical prostatectomy between 2016 and 2020. Domain summary scores for urinary incontinence and sexual function from the EPIC-26 instrument were the main outcomes, taken at 12 months following surgery (6-18 months). "Major" urinary and sexual function bother were also assessed. Variation in outcomes was investigated using linear and logistic multivariable regression models adjusted for covariates: age, socioeconomic status, PSA at diagnosis, surgical technique, surgical specimen grade group, margin status, and clinician surgical volume. RESULTS AND CONCLUSIONS: The analytic cohort included 13,083 men with the mean urinary incontinence domain score being 76/100 (SD = 25) with 9.2% reporting major bother. For sexual function, the mean score was 29/100 (SD = 26) with 46% reporting major bother. Of the examined variables, age at surgery and surgical volume category were most predictive of function, with disparities exceeding minimally important differences, though large variation was observed between urologists within volume categories. There is considerable variation in 12-month postprostatectomy functional outcomes. Variation is explained by both patient and clinician factors, though some confounders are unmeasured in this cohort.


Subject(s)
Prostatic Neoplasms , Urinary Incontinence , Male , Humans , Urinary Incontinence/epidemiology , Urinary Incontinence/etiology , Prostatectomy/adverse effects , Prostatectomy/methods , Prostatic Neoplasms/surgery , Registries , Patient Reported Outcome Measures , Quality of Life
4.
J Endocr Soc ; 5(9): bvab116, 2021 Sep 01.
Article in English | MEDLINE | ID: mdl-34308090

ABSTRACT

OBJECTIVE: Androgen deprivation therapy (ADT) reduces muscle and bone mass, increasing frailty in men with prostate cancer. The liver mediates the whole body anabolic effects of testosterone. Based on first-pass metabolism, liver-targeted testosterone treatment (LTTT) entails oral delivery of a small dose of testosterone that does not raise peripheral blood testosterone levels. LTTT reduces blood urea and stimulates protein anabolism in hypogonadal men and postmenopausal women. We investigated whether LTTT prevents loss of lean and bone mass during ADT. METHOD: A 6-month, double-blind, placebo-controlled study of testosterone 40 mg/day in 50 men. Primary outcome measures were lean mass and bone mineral content (BMC). Testosterone, urea and prostate-specific antigen (PSA) were monitored. Patients were withdrawn if PSA exceeded 4 ng/mL. RESULTS: 42 patients completed the study. Mean (95% CI) testosterone rose during LTTT but not placebo treatment [∆ 2.2 (1.3-3.0) vs -0.7 (-1.5 to 0.2) nmol/L; P < 0.01]. Mean PSA level did not change significantly during either treatment. Blood urea fell [∆ -0.4 (-0.9 to -0.1) mmol/L] during LTTT but not placebo [∆ 0.05 (-0.8 to 0.9) mmol/L]. BMC [∆ 49 (5 to 93) g; P < 0.02] and lean mass [∆ 0.8 (-0.1 to 1.7) kg; P = 0.04) increased compared to placebo. Five patients on LTTT withdrew from increased PSA levels, all returning to baseline levels. CONCLUSION: LTTT shows promise as a simple therapy for preventing sarcopenia and bone loss during ADT. LTTT may induce reversible PSA rise in some patients. Further studies are required to optimize LTTT dose in ADT. LTTT has potential application in other catabolic states in men and women.

8.
BJU Int ; 123 Suppl 5: 47-53, 2019 05.
Article in English | MEDLINE | ID: mdl-31012991

ABSTRACT

OBJECTIVE: To assess changes in lower urinary tract symptoms (LUTS) and quality of life (QoL) after robot-assisted radical prostatectomy (RARP). PATIENTS AND METHODS: A prospectively curated database of 1917 consecutive RARPs undertaken over an 8-year period from January 2009 to January 2017 was assessed. Preoperative information including age, prostate-specific antigen (PSA) level, body mass index (BMI), International Prostate Symptom Score (IPSS) and QoL score was collected, with IPSS and QoL score compared between baseline (preoperatively) and 12 months post-surgery. RESULTS: Of the 1917 patients who underwent RARP, 1470 with complete data were included in the analysis. Their mean ± sd age, prostate weight and BMI were 62 (±6.7) years, 51 (±17.6) g, and 28 kg/m2 , respectively. Overall, 57% of patients reported an improved IPSS score, whilst 76% reported an IPSS of ≤7 postoperatively. A total of 41% of patients reported an improved QoL and 90.3% of patients with severe preoperative LUTS (IPSS 20-35) demonstrated clinically improved LUTS at 1 year post RARP. The post-RARP mean IPSS in the present study was lower than those reported in the existing post-radiotherapy literature, especially in patients with moderate to severe baseline LUTS (IPSSs ≥ 8). CONCLUSIONS: At 12 months post RARP, most patients reported improved overall LUTS and QoL, with the greatest benefit seen in those patients with a high pre-RARP IPSS. This has implications for treatment selection and preoperative counselling in men being offered active treatment for their prostate cancer. Further analyses of specific IPSS domains and longer follow-up are needed.


Subject(s)
Lower Urinary Tract Symptoms/etiology , Lower Urinary Tract Symptoms/surgery , Prostatectomy/methods , Prostatic Neoplasms/complications , Prostatic Neoplasms/surgery , Quality of Life , Robotic Surgical Procedures , Aged , Body Mass Index , Follow-Up Studies , Humans , Male , Middle Aged , Patient Reported Outcome Measures , Postoperative Complications , Retrospective Studies , Survivorship
9.
Nat Rev Urol ; 15(12): 733-734, 2018 Dec.
Article in English | MEDLINE | ID: mdl-30385840
10.
Eur Urol Focus ; 4(1): 57-63, 2018 01.
Article in English | MEDLINE | ID: mdl-28753751

ABSTRACT

BACKGROUND: The development, monitoring, and reporting of indicator measures that describe standard of care provide the gold standard for assessing quality of care and patient outcomes. Although indicator measures have been reported, little evidence of their use in measuring and benchmarking performance is available. A standard set, defining numerator, denominator, and risk adjustments, will enable global benchmarking of quality of care. OBJECTIVE: To develop a set of indicators to enable assessment and reporting of quality of care for men with localised prostate cancer (PCa). DESIGN, SETTING, AND PARTICIPANTS: Candidate indicators were identified from the literature. An international panel was invited to participate in a modified Delphi process. Teleconferences were held before and after each voting round to provide instruction and to review results. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Panellists were asked to rate each proposed indicator on a Likert scale of 1-9 in a two-round iterative process. Calculations required to report on the endorsed indicators were evaluated and modified to reflect the data capture of the Prostate Cancer Outcomes Registry-Australia and New Zealand (PCOR-ANZ). RESULTS AND LIMITATIONS: A total of 97 candidate indicators were identified, of which 12 were endorsed. The set includes indicators covering pre-, intra-, and post-treatment of PCa care, within the limits of the data captured by PCOR-ANZ. CONCLUSIONS: The 12 endorsed quality measures enable international benchmarking on the quality of care of men with localised PCa. Reporting on these indicators enhances safety and efficacy of treatment, reduces variation in care, and can improve patient outcomes. PATIENT SUMMARY: PCa has the highest incidence of all cancers in men. Early diagnosis and relatively high survival rates mean issues of quality of care and best possible health outcomes for patients are important. This paper identifies 12 important measurable quality indicators in PCa care.


Subject(s)
Prostatic Neoplasms/therapy , Quality Indicators, Health Care/standards , Quality of Health Care/standards , Benchmarking , Delivery of Health Care , Delphi Technique , Humans , Male , Outcome Assessment, Health Care , Patient Outcome Assessment , Prostatic Neoplasms/epidemiology , Registries , Risk Adjustment/methods
11.
BJU Int ; 115 Suppl 5: 3-13, 2015 Apr.
Article in English | MEDLINE | ID: mdl-25327530

ABSTRACT

OBJECTIVE: To provide an up-to-date summary of current literature on the management of adverse effects of androgen-deprivation therapy (ADT). PATIENTS AND METHODS: All relevant medical literature on men with prostate cancer treated with ADT from 2005 to 2014, and older relevant papers, were reviewed. Recent health advisory statements from the Australian government, societies and advocacy groups have been incorporated to the document. RESULTS: There are numerous adverse effects of ADT that require pro-active prevention and treatment. Ranging from cardiovascular disease, diabetes and osteoporosis, to depression, cognitive decline and sexual dysfunction, the range of adverse effects is wide. Baseline assessment, monitoring, prevention and consultation from a multidisciplinary team are important in minimising the harm from ADT. CONCLUSIONS: This review provides a series of practical recommendations to assist with managing the adverse effects of ADT.


Subject(s)
Androgen Antagonists/adverse effects , Antineoplastic Agents/adverse effects , Drug-Related Side Effects and Adverse Reactions/therapy , Prostatic Neoplasms/drug therapy , Androgen Antagonists/therapeutic use , Antineoplastic Agents/therapeutic use , Drug-Related Side Effects and Adverse Reactions/prevention & control , Humans , Male
12.
J Robot Surg ; 7(4): 339-44, 2013 Dec.
Article in English | MEDLINE | ID: mdl-27001872

ABSTRACT

The aim of the study was to demonstrate an efficacious robotic fellowship model that balances safety of patients, time efficiency and adequate training, in a private hospital. Sixty-four patients underwent robot-assisted laparoscopic radical prostatectomy using a 13-step modular training programme in a single private institute. The patients were compared with 64 consecutive patients operated on by the mentoring surgeon immediately prior to the implementation of the programme. The main parameters analysed included console time, total operating time, blood loss, positive surgical margin rate and postoperative complications. There was a marginal difference in mean console time (92.67 vs. 90.41 min; p = 0.02). Statistical difference disappeared when comparing mean total operating time (136.09 vs. 134.14 min; p = 0.16), mean blood loss (165 vs. 172 ml; p = 0.96) and margin positivity (8 vs. 13; p = 0.34). The trainee was able to complete significant numbers of modular training steps whilst maintaining momentum of the operation from the commencement of the fellowship programme. This study demonstrates that a comprehensive modular training programme in complicated robotic procedures could be implemented without compromising patient safety or time efficiency.

13.
J Am Chem Soc ; 134(12): 5563-76, 2012 Mar 28.
Article in English | MEDLINE | ID: mdl-22352450

ABSTRACT

Crystallographic models of photosystem I (PS I) highlight a symmetrical arrangement of the electron transfer cofactors which are organized in two parallel branches (A, B) relative to a pseudo-C2 symmetry axis that is perpendicular to the membrane plane. Here, we explore the electron transfer pathways of PS I in whole cells of the deuterated green alga Chlamydomonas reinhardtii using high-time-resolution electron paramagnetic resonance (EPR) at cryogenic temperatures. Particular emphasis is given to quantum oscillations detectable in the tertiary radical pairs P700(+)A1A(-) and P700(+)A1B(-) of the electron transfer chain. Results are presented first for the deuterated site-directed mutant PsaA-M684H in which electron transfer beyond the primary electron acceptor A0A on the PsaA branch of electron transfer is impaired. Analysis of the quantum oscillations, observed in a two-dimensional Q-band (34 GHz) EPR experiment, provides the geometry of the B-side radical pair. The orientation of the g tensor of P700(+) in an external reference system is adapted from a time-resolved multifrequency EPR study of deuterated and 15N-substituted cyanobacteria (Link, G.; Berthold, T.; Bechtold, M.; Weidner, J.-U.; Ohmes, E.; Tang, J.; Poluektov, O.; Utschig, L.; Schlesselman, S. L.; Thurnauer, M. C.; Kothe, G. J. Am. Chem. Soc. 2001, 123, 4211-4222). Thus, we obtain the three-dimensional structure of the B-side radical pair following photoexcitation of PS I in its native membrane. The new structure describes the position and orientation of the reduced B-side quinone A1B(-) on a nanosecond time scale after light-induced charge separation. Furthermore, we present results for deuterated wild-type cells of C. reinhardtii demonstrating that both radical pairs P700(+)A1A(-) and P700(+)A1B(-) participate in the electron transfer process according to a mole ratio of 0.71/0.29 in favor of P700(+)A1A(-). A detailed comparison reveals different orientations of A1A(-) and A1B(-) in their respective binding sites such that formation of a strong hydrogen bond from A1(-) to the protein backbone is possible only in the case of A1A(-). We suggest that this is relevant to the rates of forward electron transfer from A1A(-) or A1B(-) to the iron-sulfur center F(X), which differ by a factor of 10. Thus, the present study sheds new light on the orientation of the phylloquinone acceptors in their binding pockets in PS I and the effect this has on function.


Subject(s)
Chlamydomonas reinhardtii/chemistry , Electron Spin Resonance Spectroscopy , Photosystem I Protein Complex/chemistry , Plant Proteins/chemistry , Chlamydomonas reinhardtii/cytology , Cold Temperature , Deuterium/chemistry , Electron Transport , Models, Molecular
14.
Arch Biochem Biophys ; 505(2): 160-70, 2011 Jan 15.
Article in English | MEDLINE | ID: mdl-20933495

ABSTRACT

The relationship between membrane protein structure and thermal stability has been examined in the reaction centre from the bacterium Rhodobacter sphaeroides, a complex membrane protein comprising three polypeptide chains and 10 cofactors. The core of this protein exhibits an approximate twofold symmetry, the cofactors being held in two membrane-spanning branches by two polypeptides, termed L and M, that have very similar folds. In assays of the thermal stability of wild-type and mutant reaction centres embedded in the native bilayer membrane, replacement of a Phe at position 197 of the M polypeptide by His produced an increase in stability, whereas an opposing replacement of His by Phe at the symmetrical position 168 of the L-polypeptide produced a decrease in stability. In light of the known X-ray crystal structures of wild-type and mutant variants of this protein, and further mutagenesis, it is concluded that these stability changes result from the introduction or removal, respectively, of a hydrogen bond between the side-chain of the His and that of an Asn located two positions along the M or L polypeptide chain, in addition to a hydrogen bond between the His side-chain and an adjacent bacteriochlorophyll cofactor.


Subject(s)
Membrane Proteins/chemistry , Membrane Proteins/metabolism , Peptides/chemistry , Photosynthetic Reaction Center Complex Proteins/chemistry , Photosynthetic Reaction Center Complex Proteins/metabolism , Temperature , Coenzymes/chemistry , Coenzymes/metabolism , Enzyme Stability , Hydrogen Bonding , Kinetics , Membrane Proteins/genetics , Models, Molecular , Mutagenesis, Site-Directed , Mutation , Photosynthetic Reaction Center Complex Proteins/genetics , Protein Conformation , Protein Engineering , Protein Unfolding , Rhodobacter sphaeroides
15.
FEBS J ; 275(20): 5090-107, 2008 Oct.
Article in English | MEDLINE | ID: mdl-18959769

ABSTRACT

NAD is an important cofactor and essential molecule in all living organisms. In many eubacteria, including several pathogens, the first two steps in the de novo synthesis of NAD are catalyzed by l-aspartate oxidase (NadB) and quinolinate synthase (NadA). Despite the important role played by these two enzymes in NAD metabolism, many of their biochemical and structural properties are still largely unknown. In the present study, we cloned, overexpressed and characterized NadA and NadB from Bacillus subtilis, one of the best studied bacteria and a model organism for low-GC Gram-positive bacteria. Our data demonstrated that NadA from B. subtilis possesses a [4Fe-4S]2+ cluster, and we also identified the cysteine residues involved in the cluster binding. The [4Fe-4S]2+ cluster is coordinated by three cysteine residues (Cys110, Cys230, and Cys320) that are conserved in all the NadA sequences reported so far, suggesting a new noncanonical binding motif that, on the basis of sequence alignment studies, may be common to other quinolinate synthases from different organisms. Moreover, for the first time, it was shown that the interaction between NadA and NadB is not species-specific between B. subtilis and Escherichia coli.


Subject(s)
Amino Acid Oxidoreductases/chemistry , Bacillus subtilis/enzymology , Multienzyme Complexes/chemistry , Amino Acid Oxidoreductases/genetics , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Binding Sites , Cloning, Molecular , Conserved Sequence , Cysteine , Escherichia coli Proteins , Iron-Sulfur Proteins , Multienzyme Complexes/genetics , Species Specificity
17.
J Biol Chem ; 283(16): 10559-67, 2008 Apr 18.
Article in English | MEDLINE | ID: mdl-18252716

ABSTRACT

During chlorophyll and bacteriochlorophyll biosynthesis in gymnosperms, algae, and photosynthetic bacteria, dark-operative protochlorophyllide oxidoreductase (DPOR) reduces ring D of aromatic protochlorophyllide stereospecifically to produce chlorophyllide. We describe the heterologous overproduction of DPOR subunits BchN, BchB, and BchL from Chlorobium tepidum in Escherichia coli allowing their purification to apparent homogeneity. The catalytic activity was found to be 3.15 nmol min(-1) mg(-1) with K(m) values of 6.1 microm for protochlorophyllide, 13.5 microm for ATP, and 52.7 microm for the reductant dithionite. To identify residues important in DPOR function, 21 enzyme variants were generated by site-directed mutagenesis and investigated for their metal content, spectroscopic features, and catalytic activity. Two cysteine residues (Cys(97) and Cys(131)) of homodimeric BchL(2) are found to coordinate an intersubunit [4Fe-4S] cluster, essential for low potential electron transfer to (BchNB)(2) as part of the reduction of the protochlorophyllide substrate. Similarly, Lys(10) and Leu(126) are crucial to ATP-driven electron transfer from BchL(2). The activation energy of DPOR electron transfer is 22.2 kJ mol(-1) indicating a requirement for 4 ATP per catalytic cycle. At the amino acid level, BchL is 33% identical to the nitrogenase subunit NifH allowing a first tentative structural model to be proposed. In (BchNB)(2), we find that four cysteine residues, three from BchN (Cys(21), Cys(46), and Cys(103)) and one from BchB (Cys(94)), coordinate a second inter-subunit [4Fe-4S] cluster required for catalysis. No evidence for any type of molybdenum-containing cofactor was found, indicating that the DPOR subunit BchN clearly differs from the homologous nitrogenase subunit NifD. Based on the available data we propose an enzymatic mechanism of DPOR.


Subject(s)
Adenosine Triphosphate/metabolism , Chlorobium/metabolism , Nitrogenase/chemistry , Oxidoreductases/metabolism , Protochlorophyllide/chemistry , Adenosine Triphosphate/chemistry , Catalysis , Cysteine/chemistry , Dithionite/chemistry , Electrons , Escherichia coli/metabolism , Heme/chemistry , Kinetics , Leucine/chemistry , Light , Lysine/chemistry
18.
Biochim Biophys Acta ; 1777(4): 327-30, 2008 Apr.
Article in English | MEDLINE | ID: mdl-18243125

ABSTRACT

The alternative oxidase is a respiratory chain protein found in plants, fungi and some parasites that still remains physically uncharacterised. In this report we present EPR evidence from parallel mode experiments which reveal signals at approximately g=16 in both purified alternative oxidase protein (g=16.9), isolated mitochondrial membranes (g=16.1), and in trypanosomal AOX expressed in Escherichia coli membranes (g=16.4). Such signals are indicative of a dicarboxylate diiron centre at the active site of the enzyme. To our knowledge these data represent the first EPR signals from AOX present in its native environment.


Subject(s)
Iron/chemistry , Oxidoreductases/chemistry , Animals , Binding Sites , Electron Spin Resonance Spectroscopy , Electron Transport , Mitochondrial Membranes/chemistry , Mitochondrial Membranes/enzymology , Mitochondrial Proteins , Plant Proteins , Trypanosoma/enzymology
19.
J Biol Chem ; 282(33): 23957-69, 2007 Aug 17.
Article in English | MEDLINE | ID: mdl-17567575

ABSTRACT

Ring contraction during cobalamin (vitamin B12) biosynthesis requires a seemingly futile methylation of the C20 position of the tetrapyrrole framework. Along the anaerobic route, this reaction is catalyzed by CbiL, which transfers a methyl group from S-adenosyl-L-methionine to cobalt factor II to generate cobalt factor III. CbiL belongs to the class III methyltransferases and displays similarity to other cobalamin biosynthetic methyltransferases that are responsible for the regiospecific methylation of a number of positions on the tetrapyrrole molecular canvas. In an attempt to understand how CbiL selectively methylates the C20 position, a detailed structure function analysis of the enzyme has been undertaken. In this paper, we demonstrate that the enzyme methylates the C20 position, that its preferred substrate is cobalt factor II, and that the metal ion does not undergo any oxidation change during the course of the reaction. The enzyme was crystallized, and its structure was determined by x-ray crystallography, revealing that the 26-kDa protein has a similar overall topology to other class III enzymes. This helped in the identification of some key amino acid residues (Asp(104), Lys(176), and Tyr(220)). Analysis of mutant variants of these groups has allowed us to suggest potential roles that these side chains may play in substrate binding and catalysis. EPR analysis of binary and ternary complexes indicate that the protein donates a fifth ligand to the cobalt ion via a gated mechanism to prevent transfer of the methyl group to water. The chemical logic underpinning the methylation is discussed.


Subject(s)
Methanobacteriaceae/enzymology , Methyltransferases/chemistry , Vitamin B 12/chemistry , Bacterial Proteins , Catalysis , Crystallography, X-Ray , Electron Spin Resonance Spectroscopy , Ligands , Methylation , Methyltransferases/metabolism , Protein Conformation , Substrate Specificity , Vitamin B 12/metabolism
20.
Biochim Biophys Acta ; 1757(11): 1529-38, 2006 Nov.
Article in English | MEDLINE | ID: mdl-16945322

ABSTRACT

We studied the kinetics of reoxidation of the phylloquinones in Chlamydomonas reinhardtii Photosystem I using site-directed mutations in the PhQ(A)-binding site and of the residues serving as the axial ligand to ec3(A) and ec3(B) chlorophylls. In wild type PS I, these kinetics are biphasic, and mutations in the binding region of PhQ(A) induced a specific slowing down of the slow component. This slowing allowed detection of a previously unobserved 180-ns phase having spectral characteristics that differ from electron transfer between phylloquinones and F(X). The new kinetic phase thus reflects a different reaction that we ascribe to oxidation of F(X)(-) by the F(A/B) FeS clusters. These absorption changes partly account for the differences between the spectra associated with the two kinetic components assigned to phylloquinone reoxidation. In the mutant in which the axial ligand to ec3(A) (PsaA-Met688) was targeted, about 25% of charge separations ended in P(700)(+)A(0)(-) charge recombination; no such recombination was detected in the B-side symmetric mutant. Despite significant changes in the amplitude of the components ascribed to phylloquinone reoxidation in the two mutants, the overall nanosecond absorption changes were similar to the wild type. This suggests that these absorption changes are similar for the two different phylloquinones and that part of the differences between the decay-associated spectra of the two components reflect a contribution from different electron acceptors, i.e. from an inter-FeS cluster electron transfer.


Subject(s)
Electrons , Photosystem I Protein Complex/chemistry , Absorption , Animals , Chlamydomonas/genetics , Chlamydomonas/metabolism , Iron-Sulfur Proteins/chemistry , Kinetics , Ligands , Models, Chemical , Models, Molecular , Mutagenesis, Site-Directed , Mutation , Oxygen/metabolism , Spectrophotometry , Ultraviolet Rays
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