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At least 793 records · Page 44Linked to original sources
PubMed1997

Stability of protease inhibitors based on the Bowman-Birk reactive site loop to hydrolysis by proteases.

Bowman-Birk proteinase inhibitor proteins contain two inhibitory regions, each of which is encapsulated within nine-residue disulfide-linked loops. It is known that short cyclic peptides that retain the nine-residue disulfide-bridged motif have inhibitory activity, and can be used as models of the natural inhibitor protein. Two factors are important in determining the effectiveness of such inhibitor peptides: the value of the inhibition constant, and rate at which the inhibitor peptide is hydrolyzed by the proteinase. In this paper we report a study of the inhibitory properties and stability towards proteolytic hydrolysis of a family of synthetic peptides derived from the trypsin reactive site loop of the Bowman-Birk inhibitors. The addition of a single amino acid residue to each end of the nine-residue disulfide-linked loop is found to reduce the rate at which the peptide is hydrolyzed. In addition, changing the P2' residue from Asn-->Ile gives inhibitors with considerably enhanced stability to proteolysis, as well as reduced values of Ki. The implications of these factors for the design of inhibitors based on this loop motif is discussed.

Acetylation↗
PubMed2006

RNA silencing suppression by a second copy of the P1 serine protease of Cucumber vein yellowing ipomovirus, a member of the family Potyviridae that lacks the cysteine protease HCPro.

The P1 protein of viruses of the family Potyviridae is a serine proteinase, which is highly variable in length and sequence, and its role in the virus infection cycle is not clear. One of the proposed activities of P1 is to assist HCPro, the product that viruses of the genus Potyvirus use to counteract antiviral defense mediated by RNA silencing. Indeed, an HCPro-coding region is present in all the genomes of members of the genera Potyvirus, Rymovirus, and Tritimovirus that have been sequenced. However, it was recently reported that a sequence coding for HCPro is lacking in the genome of Cucumber vein yellowing virus (CVYV), a member of the genus Ipomovirus, the fourth monopartite genus of the family. In this study, we provide further evidence that P1 enhances the activity of HCPro in members of the genus Potyvirus and show that it is duplicated in the ipomovirus CVYV. The two CVYV P1 copies are arranged in tandem, and the second copy (P1b) has RNA silencing suppression activity. CVYV P1b suppressed RNA silencing induced either by sense green fluorescent protein (GFP) mRNA or by a GFP inverted repeat RNA, indicating that CVYV P1b acts downstream of the formation of double-stranded RNA. CVYV P1b also suppressed local silencing in agroinfiltrated patches of transgenic Nicotiana benthamiana line 16c and delayed its propagation to the neighboring cells. However, neither the short-distance nor long-distance systemic spread of silencing of the GFP transgene was completely blocked by CVYV P1b. CVYV P1b and P1-HCPro from the potyvirus Plum pox virus showed very similar behaviors in all the assays carried out, suggesting that evolution has found a way to counteract RNA silencing by similar mechanisms using very different proteins in viruses of the same family.

Gene Duplication↗
PubMed1976

Acid proteases from species of Mucor. IV. Hydrogen-tritium exchange of Mucor miehei protease.

The kinetics of hydrogen-tritium exchange were studied in the range pH-3 for both the fully and partially tritiated protein. Exchange constants for an intermediate class and slow class of hydrogens were determined and found to give a parabolic curve characteristic of acid and base catalysis about the observed pHmin of 4.03. The anomalous rate retardation on the acid portion of the curve was attributed to electrostatic interactions which could be evaluated quantitatively from the titration data. Partial tritation and pH cross-over experiments indicated that the rank order was pH-independent thus eliminating the possiblitity of a major conformational change. Consequently, the data are most likely explicable in terms of restricted solvent accessibility.

Hydrogen-Ion Concentration↗