Co-evolution of drug resistance and broadened substrate recognition in HIV protease variants isolated from an Escherichia coli genetic selection system.

A genetic selection system for activity of HIV protease is described that is based on a synthetic substrate constructed as a modified AraC regulatory protein that when cleaved stimulate l-arabinose metabolism in an Escherichia coli araC strain. Growth stimulation on selective plates was shown to depend on active HIV protease and the scissile bond in the substrate. In addition, the growth of cells correlated well with the established cleavage efficiency of the sites in the viral polyprotein, Gag, when these sites were individually introduced into the synthetic substrate of the selection system. Plasmids encoding protease variants selected based on stimulation of cell growth in the presence of saquinavir or cleavage of a site not cleaved by wild-type protease, were indistinguishable with respect to both phenotypes. Also, both groups of selected plasmids encoded side chain substitutions known from clinical isolates or displayed different side chain substitutions but at identical positions. One highly frequent side chain substitution, E34V, not regarded as a major drug resistance substitution was found in variants obtained under both selective conditions and is suggested to improve protease processing of the synthetic substrate. This substitution is away from the substrate-binding cavity and together with other substitutions in the selected reading frames supports the previous suggestion of a substrate-binding site extended from the active site binding pocket itself.

Positive staining for cellulose in oral pulse granuloma.

OBJECTIVE: Oral pulse granuloma (OPG) is an oral inflammatory lesion characterized by the presence of hyaline rings with numerous multinucleated giant cells. The etiopathogenesis of this lesion is thus far unclear, as is the composition of the hyaline rings. Our aim was to investigate whether the hyaline rings contain cellulose. STUDY DESIGN: Using a newly developed staining method for cellulose, we studied 18 histologic samples diagnosed as OPG, in addition to 3 samples originally diagnosed as "normal" foreign body reactions. In our study, visualization of cellulose is based on its specific binding to the carbohydrate binding module of ß-1,4-glycanase. RESULTS: All samples diagnosed as OPG were positive for cellulose staining localized in hyaline rings. In addition, 1 lesion (of 3), first diagnosed as a foreign body reaction without the presence of hyaline rings, was positive for cellulose by horseradish peroxidase staining. CONCLUSIONS: We show for the first time that cellulose is present in OPG lesions, indicating that cellulose might be the initial cause of formation of these lesions.

The human selenoprotein VCP-interacting membrane protein (VIMP) is non-globular and harbors a reductase function in an intrinsically disordered region.

The human selenoprotein VIMP (VCP-interacting membrane protein)/SelS (selenoprotein S) localizes to the endoplasmic reticulum (ER) membrane and is involved in the process of ER-associated degradation (ERAD). To date, little is known about the presumed redox activity of VIMP, its structure and how these features might relate to the function of the protein in ERAD. Here, we use the recombinantly expressed cytosolic region of VIMP where the selenocysteine (Sec) in position 188 is replaced with a cysteine (a construct named cVIMP-Cys) to characterize redox and structural properties of the protein. We show that Cys-188 in cVIMP-Cys forms a disulfide bond with Cys-174, consistent with the presence of a Cys174-Sec188 selenosulfide bond in the native sequence. For the disulfide bond in cVIMP-Cys we determined the reduction potential to -200 mV, and showed it to be a good substrate of thioredoxin. Based on a biochemical and structural characterization of cVIMP-Cys using analytical gel filtration, CD and NMR spectroscopy in conjunction with bioinformatics, we propose a comprehensive overall structural model for the cytosolic region of VIMP. The data clearly indicate the N-terminal half to be comprised of two extended α-helices followed by a C-terminal region that is intrinsically disordered. Redox-dependent conformational changes in cVIMP-Cys were observed only in the vicinity of the two Cys residues. Overall, the redox properties observed for cVIMP-Cys are compatible with a function as a reductase, and we speculate that the plasticity of the intrinsically disordered C-terminal region allows the protein to access many different and structurally diverse substrates.

Trisulfides in proteins.

Trisulfides and other oligosulfides are widely distributed in the biological world. In plants, for example, garlic, trisulfides are associated with potentially beneficial properties. However, an extra neutral sulfur atom covalently bound between the two sulfur atoms of a pair of cysteines is not a common post-translational modification, and the number of proteins in which a trisulfide has been unambiguously identified is small. Nevertheless, we believe that its prevalence may be underestimated, particularly with the increasing evidence for significant pools of sulfides in living tissues and their possible roles in cellular metabolism. This review focuses on examples of proteins that are known to contain a trisulfide bridge, and gives an overview of the chemistry of trisulfide formation, and the methods by which it is detected in proteins.