Synthesis and conformational properties of a synthetic cyclic peptide for the active site of alpha-chymotrypsin

Cobra CRISP functions as an inflammatory modulator via a novel Zn2+- and heparan sulfate-dependent transcriptional regulation of endothelial cell adhesion molecules

Cysteine-rich secretory proteins (CRISPs) have been identified as a toxin family in most animal venoms with biological functions mainly associated with the ion channel activity of cysteine-rich domain (CRD). CRISPs also bind to Zn(2+) at their N-terminal pathogenesis-related (PR-1) domain, but their function remains unknown. Interestingly, similar the Zn(2+)-binding site exists in all CRISP family, including those identified in a wide range of organisms. Here, we report that the CRISP from Naja atra (natrin) could induce expression of vascular endothelial cell adhesion molecules, i.e. intercellular adhesion molecule-1, vascular adhesion molecule-1, and E-selectin, to promote monocytic cell adhesion in a heparan sulfate (HS)- and Zn(2+)-dependent manner. Using specific inhibitors and small interfering RNAs, the activation mechanisms are shown to involve both mitogen-activated protein kinases and nuclear factor-κB. Biophysical characterization of natrin by using fluorescence, circular dichroism, and x-ray crystallographic methods further reveals the presence of two Zn(2+)-binding sites for natrin. The strong binding site is located near the putative Ser-His-Glu catalytic triad of the N-terminal domain. The weak binding site remains to be characterized, but it may modulate HS binding by enhancing its interaction with long chain HS. Our results strongly suggest that natrin may serve as an inflammatory modulator that could perturb the wound-healing process of the bitten victim by regulating adhesion molecule expression in endothelial cells. Our finding uncovers a new aspect of the biological role of CRISP family in immune response and is expected to facilitate future development of new therapeutic strategy for the envenomed victims.

Liquid-phase combinatorial synthesis: in search of small-molecule enzyme mimics

The applications, advantages and recent advances in liquid-phase combinatorial chemistry using poly-(ethyleneglycol) as a soluble polymer support are reviewed. Our recent efforts towards the synthesis of peptide-based catalysts on polyethyleneglycol are reported. The screening of libraries of peptides for catalysis is discussed.

The stereochemistry of peptides containing alpha-aminoisobutyric acid

The introduction of alpha-aminoisobutyric acid (Aib) into peptides dramatically limits the range of accessible backbone conformations. The presence of two geminal methyl groups at C alpha sterically compels Aib residues to largely favor structures in the right- or left-handed 3(10)/alpha-helical regions (phi approximately +/- 60 +/- 20 degrees, psi approximately +/- 30 +/- 20 degrees) of the peptide conformational map. Aib residues occur extensively in microbial peptides which form transmembrane channels. This observation has stimulated considerable interest in the stereochemistry of Aib peptides. This review summarizes theoretical studies on the conformations of Aib residues and examines the available data on solid-state structures, derived from single crystal X-ray diffraction studies. Crystal structures of over three dozen Aib-containing peptides, ranging in length from 2 to 11 residues, have been reported so far which exemplify various types of beta-turns, consecutive beta-turns, and helical structures. Examples of nonhydrogen bonded and cyclic structures are also described. The crystallographic results compare well with structural studies in solution, establishing that Aib peptides can provide rigid structural models for the development of spectroscopic methods of peptide conformational analysis.