High resolution X-ray analyses of renin inhibitor-aspartic proteinase complexes

Inhibitors of the conversion of angiotensinogen to the vasoconstrictor angiotensin II have considerable value as antihypertensive agents. For example, captopril and enalapril are clinically useful as inhibitors of angiotensin-converting enzyme. This has encouraged intense activity in the development of inhibitors of kidney renin, which is a very specific aspartic proteinase catalysing the first and rate limiting step in the conversion of angiotensinogen to angiotensin II. The most effective inhibitors such as H-142 and L-363,564 have used non-hydrolysable analogues of the proposed transition state, and partial sequences of angiotensinogen (Table 1). H-142 is effective in lowering blood pressure in humans but has no significant effect on other aspartic proteinases such as pepsin in the human body (Table 1). At present there are no crystal structures available for human or mouse renins although three-dimensional models demonstrate close structural similarity to other spartic proteinases. We have therefore determined by X-ray analysis the three-dimensional structures of H-142 and L-363,564 complexed with the aspartic proteinase endothiapepsin, which binds these inhibitors with affinities not greatly different from those measured against human renin (Table 1). The structures of these complexes and of that between endothiapepsin and the general aspartic proteinase inhibitor, H-256 (Table 1) define the common hydrogen bonding schemes that allow subtle differences in side-chain orientations and in the positions of the transition state analogues with respect to the active-site aspartates.     

Evaluation in vitro of an Experimental Antibacterial Silk Suture

Because of good clinical performance and low cost,silk braided surgical suture becomes one of excellent and widely used sutures. But as a kind of natural protein fiber,silk easily trends to microbial infection. Beyond that,braided structure may increase the risk of hide of bacteria. Hence,the project of this study is to develop a novel antibacterial silk braided suture. Silk braided sutures were treated with antimicrobial solution which added antimicrobial agent4-quinolones into 5% polycaprolactone( PCL) solution. Then sutures were tested for in vitro efficacy against Staphylococcus aureus(S. aureus) and Escherichia coli(E. coli) by a zone of inhibition assay,and sustained efficacy assay,release of antibacterial agent,SEM photographs against S. aureus. Treated sutures exhibited distinct zones of inhibition against S. aureus and E. coli. They also kept antimicrobial property against S. aureus for 7 d,which were almost equal with coated VICRYL*Plus sutures. The highest release concentration of treated suture was 1. 53 mg /L,which was lower than Cmaxof 4-quinolones,proved the safety of antibacterial silk suture. SEM photographs gave both the change of the surface and different bacteria growth situations on the surface before and after treating.     

X-ray analyses of peptide-inhibitor complexes define the structural basis of specificity for human and mouse renins.

X-ray analyses have defined the three-dimensional structures of crystals of mouse and human renins complexed with peptide inhibitors at resolutions of 1.9 and 2.8 A, respectively. The exquisite specificity of renin arises partly from ordered loop regions at the periphery of the binding cleft. Although the pattern of main-chain hydrogen bonding in other aspartic proteinase inhibitor complexes is conserved in renins, differences in the positions of secondary structure elements (particularly helices) also lead to improved specificity in renins for angiotensinogen substrates.     

Beta-hairpin families in globular proteins

Beta-hairpins, one of the simplest supersecondary structures, are widespread in globular proteins, and have often been suggested as possible sites for nucleation. Here we consider the conformation and sequences of the loop regions of beta-hairpins by analysing proteins of known structure. We find that the 'tight' beta-hairpins, classified by the length and conformations of their loop regions, form distinct families and that the loop regions of the family members have sequences which are characteristic of that family. The two-residue hairpin loops include almost entirely I' or II' beta-turns, in contrast to the general preference for type I and type II turns. These findings are being used to help define templates or consensus sequences to be incorporated into our existing supersecondary structure prediction algorithm. This information can also be used in model-building homologous proteins.     

Knowledge-based prediction of protein structures and the design of novel molecules

Prediction of the tertiary structures of proteins may be carried out using a knowledge-based approach. This depends on identification of analogies in secondary structures, motifs, domains or ligand interactions between a protein to be modelled and those of known three-dimensional structures. Such techniques are of value in prediction of receptor structures to aid the design of drugs, herbicides or pesticides, antigens in vaccine design, and novel molecules in protein engineering.