Identification of a core domain within the proregion of bone morphogenetic proteins that interacts with the dimeric, mature domain.

Proregions of bone morphogenetic proteins (BMPs) fulfill important biological functions as intramolecular chaperones and for extracellular targeting of the mature signal ligand. Knowledge of the structures of the proregions would contribute to a more comprehensive picture of the biological activities of the pro-forms of BMP growth factors. In this study, a protease resistant core domain of the proregions of three BMPs was identified. For a more detailed analysis, the core domain of the BMP-2 proregion was recombinantly produced. Unfolding/refolding experiments and spectroscopic analyses proved that the core domain can be obtained as a folded entity. Binding of the core domain to the mature growth factor was demonstrated by SPR. Via peptide microarray analysis, residues within the core fragment could be identified that engage in binding to the dimeric, mature domain. Our study reveals that diverse members of the BMP family share a common, independently folding core domain within the large proregions peculiar to TGF-ß superfamily members that may serve as a scaffold for folding and assembly of the dimeric proprotein complexes.

Identification of nascent chain interaction sites on trigger factor.

The role of ribosome-binding molecular chaperones in protein folding is not yet well understood. Trigger factor (TF) is the first chaperone to interact with nascent polypeptides as they emerge from the bacterial ribosome. It binds to the ribosome as a monomer but forms dimers in free solution. Based on recent crystal structures, TF has an elongated shape, with the peptidyl-prolyl-cis/trans-isomerase (PPIase) domain and the N-terminal ribosome binding domain positioned at opposite ends of the molecule and the C-terminal domain, which forms two arms, positioned in between. By using site specifically labeled TF proteins, we have demonstrated that all three domains of TF interact with nascent chains during translation. Interactions with the PPIase domain were length-dependent but independent of PPIase activity. Interestingly, with free TF, these same sites were found to be involved in forming the dimer interface, suggesting that dimerization partially occludes TF-nascent chain binding sites. Our data indicate the existence of two regions on TF along which nascent chains can interact, the NC-domains as the main site and the PPIase domain as an auxiliary site.

Exploring the capacity of trigger factor to function as a shield for ribosome bound polypeptide chains.

Ribosome-bound trigger factor (TF) is the first chaperone encountered by a nascent polypeptide chain in bacteria. TF has been proposed to form a cradle-shaped shield for nascent chains up to approximately 130 residues to fold in a protected environment upon exit from the ribosome. We report that nascent chains of luciferase up to 280 residues in length are relatively protected by TF against digestion by proteinase K. In contrast, nascent chains of the constitutively unstructured protein alpha-synuclein were not protected, although they were in close proximity to TF by crosslinking. Thus, TF is not a general shield for nascent chains. Protease protection appears to depend on a hydrophobic interaction of TF with nascent polypeptides.

Indene bioconversion by a toluene inducible dioxygenase of Rhodococcus sp. I24.

Rhodococcus sp. I24 can oxygenate indene via at least three independent enzyme activities: (i) a naphthalene inducible monooxygenase (ii) a naphthalene inducible dioxygenase, and (iii) a toluene inducible dioxygenase (TID). Pulsed field gel analysis revealed that the I24 strain harbors two megaplasmids of approximately 340 and approximately 50 kb. Rhodococcus sp. KY1, a derivative of the I24 strain, lacks the approximately 340 kb element as well as the TID activity. Southern blotting and sequence analysis of an indigogenic, I24-derived cosmid suggested that an operon encoding a TID resides on the approximately 340 kb element. Expression of the tid operon was induced by toluene but not by naphthalene. In contrast, naphthalene did induce expression of the nid operon, encoding the naphthalene dioxygenase in I24. Cell free protein extracts of Escherichia coli cells expressing tidABCD were used in HPLC-based enzyme assays to characterize the indene bioconversion of TID in vitro. In addition to 1-indenol, indene was transformed to cis-indandiol with an enantiomeric excess of 45.2% of cis-(1S,2R)-indandiol over cis-(1R,2S)-indandiol, as revealed by chiral HPLC analysis. The Km of TID for indene was 380 microM. The enzyme also dioxygenated naphthalene to cis-dihydronaphthalenediol with an activity of 78% compared to the formation of cis-indandiol from indene. The Km of TID for naphthalene was 28 microM. TID converted only trace amounts of toluene to 1,2-dihydro-3-methylcatechol after prolonged incubation time. The results indicate the role of the tid operon in the bioconversion of indene to 1-indenol and cis-(1S,2R)-indandiol by Rhodococcus sp. I24.

Quantitation of the spliced late gene of human cytomegalovirus and its kinetics during experimental infection.

Human cytomegalovirus (hCMV) infection is still a cause of morbidity and mortality after solid organ and bone marrow transplantation and in other immunocompromised states. 'Preemptive therapy' strategies necessitate sensitive and specific methods for rapid diagnosis of symptomatic hCMV infection and monitoring of antiviral treatment. For analysis of the lytic stage of viral replication, the molecular determination of late transcripts is a useful approach for diagnosis of hCMV disease. In the present study we established an absolute quantitation of hCMV spliced late gene (SLG) RNA transcripts by real-time reverse transcription-polymerase chain reaction. Intron spanning primers were used for amplification to discriminate between viral DNA and cDNA. For standardization of the varying amounts of cDNA analyzed, cytoplasmic beta2-microglobulin (beta2-MG) cDNA was quantitated in parallel. cDNA copy numbers of both target sequences could be quantitated in a wide linear range from 10 to 10(7) copies. To investigate the applicability of the developed assay, diploid lung fibroblasts were infected with the virus strain AD169. SLG expression was measured during a 48-h period after inoculation. After an only low expression during the first 10 h (approximately 5 x 10(2) copies/sample or SLG/beta2-MG ratio <0.001), SLG transcription increased dramatically after 24 h, peaking at 5x104 copies/sample or SLG/beta2-MG ratio of 0.035 after 48 h. Intra- and interassay variability was less than 5% for calibrators and less than 10% samples. We conclude that quantitation of SLG transcripts by the presented method might be a powerful tool for differentiating between hCMV latency and active replication in vitro end in vivo, and thus may be a promising tool for diagnosis of symptomatic hCMV infection and monitoring of antiviral treatment.