Involvement of the Arg566 residue of Aeromonas sobria serine protease in substrate specificity.

Aeromonas sobria serine protease (ASP) is an extracellular serine protease secreted by the organism. Here, we identified the amino acid residue of ASP that contributes to substrate specificity by using both synthetic peptides and biological protein components. The results showed that the arginine residue at position 566 (Arg-566) of ASP, which is located in the extra occluding region of ASP close to an entrance of the catalytic cavity, is involved in the substrate specificity. A substitutional point mutation of the Arg-566 residue of ASP to Ala residue (ASP[R566A]) caused a decrease of the proteolytic efficiency for a certain substrate. In addition, ASP lost the ability to recognize the primary substrate by such a point mutation, and ASP[R566A] reacted to a wide range of synthetic substrates. It is likely that Arg-566 causes an interaction with the amino acid residue at position P3 of the substrate, which is the third amino acid residue upstream from the cleavage site. Another study using ORF2 protein, a chaperone protein of ASP, further suggested that Arg-566 could also play an important role in interaction with ORF2. We therefore conclude that the Arg-566 residue of ASP is likely responsible for the selection of substrates.

Computational design of a sulfoglucuronide derivative fitting into a hydrophobic pocket of dengue virus E protein.

We performed first-principles calculations based on the ab initio fragment molecular orbital method on dengue virus envelope protein with a hydrophobic ligand, octyl-ß-D-glucose to develop an entry inhibitor. As several polar amino acid residues are present at the edge of the pocket, the glucose moiety was chemically modified with hydrophilic groups. Introduction of both sulfated and carboxylated groups on glucose enhanced not only binding affinity to the protein but also inhibition of dengue virus entry. Octyl-2-O-sulfo ß-D-glucuronic acid may serve as a molecular probe to study the dengue virus entry process.

2-(Benzothiazol-2-yl)-phenyl-ß-d-galactopyranoside derivatives as fluorescent pigment dyeing substrates and their application for the assay of ß-d-galactosidase activities.

2-(Benzothiazol-2-yl)-phenyl-ß-d-galactopyranoside derivatives were synthesized as novel artificial fluorescent pigment dyeing substrates for ß-d-galactosidase. The substrates, which exhibited non-fluorescence or weak fluorescence in solution phase, were smoothly hydrolyzed by ß-d-galactosidase from Aspergillus oryzae and yielded a water-insoluble strong fluorescent pigment. The difference of fluorescent intensity exhibited a linear relationship with the amount of enzyme.

Effects of chemical modification of ursodeoxycholic acid on TGR5 activation.

The aim of this study is to examine the ability of the bile acid analogues obtained by chemical modification of ursodeoxycholic acid (UDCA) for TGR5 activation. Eleven UDCA analogues including 3- or 7-methylated UDCAs and amino acid conjugates were investigated as to their ability to activate TGR5 by means of the luciferase assay. It was noteworthy that 7α-methylated UDCA, namely 3α,7ß-dihydroxy-7α-methyl-5ß-cholanoic acid, had a significantly high affinity for and ability to activate TGR5 as compared to UDCA. Additionally, FXR activation ability of 7α-methylated UDCA was low relative to that of UDCA. However, other modification of UDCA, such as the introduction of methyl group at its C-3 position and oxidation or epimerization of hydroxyl group in the C-3 position, could not elicit such remarkable effect. The present findings would provide a useful strategy for the development of TGR5-selective agonist.