Biomedical subjects
Publications and source records attributed to Yi-An Lu.
[reaction: see text] Peptide ligation of noncysteinyl residues can be achieved conveniently by a reversible C-terminal thiol handle together with a Ag(+) ion-assisted S,N-acyl migration. The regenerated C-terminal handle permits tandem ligation of multiple segment.
The electrostatic interaction of the charge cluster of an amphipathic peptide antibiotic with microbial membranes is a salt-sensitive step that often determines organism specificity. We have examined the correlation between charge clusters and salt insensitivity and microbial specificity in linear, cyclic, and retro-isomeric cystine-stabilized beta-strand (CSbeta) tachyplesin (TP) in a panel of 10 test organisms. Cyclic tachyplesins consisting of 14 and 18 amino acids are constrained by an end-to-end peptide backbone and two or three disulfide bonds to cross-brace the anti-parallel beta-strand that approximates a "beta-tile" structure. Circular dichroism measurements of beta-tile TPs showed that they displayed ordered structures. Control peptides containing the same number of basic amino acids as TP but lacking disulfide constraints were highly salt sensitive. Cyclic TP analogues with six cationic charges were more broadly active and salt-insensitive than those with fewer cationic charges. Reducing their proximity or number of cationic charges, particularly those with three or fewer basic amino acids, led to a significant decrease in potency and salt insensitivity, but an increased selectivity to certain Gram-positive bacteria. An end-group effect of the dibasic N-terminal Lys of TP in the open-chain TP and its retroisomer was observed in certain Gram-negative bacteria under high-salt conditions, an effect that was not found in the cyclic analogs. These results suggest that a stable folded structure together with three or more basic amino acids closely packed in a charged region in CSbeta peptides is important for salt insensitivity and organism specificity.
Dendrimeric peptides selective for microbial surfaces have been developed to achieve broad antimicrobial activity and low hemolytic activity to human erythrocytes. The dendrimeric core is an asymmetric lysine branching tethered with two to eight copies of a tetrapeptide (R4) or an octapeptide (R8). The R4 tetrapeptide (RLYR) contains a putative microbial surface recognition BHHB motif (B = basic, H = hydrophobic amino acid) found in protegrins and tachyplesins whereas the octapeptide R8 (RLYRKVYG) consists of an R4 and a degenerated R4 repeat. Antimicrobial assays against 10 organisms in high- and low-salt conditions showed that the R4 and R8 monomers as well as their divalent dendrimers contain no to low activity. In contrast, the tetra- and octavalent R4 and R8 dendrimers are broadly active under either conditions, exhibiting relatively similar potency with minimal inhibition concentrations < 1 microm against both bacteria and fungi. Based on their size and charge similarities, the potency and activity spectrum of the tetravalent R4 dendrimer are comparable to protegrins and tachyplesins, a family of potent antimicrobials containing 17-19 residues. Compared with a series of linearly repeating R4 peptides, the R4 dendrimers show comparable antimicrobial potency, but are more aqueous soluble, more stable to proteolysis, less toxic to human cells and more easily synthesized chemically. These results suggest repeating peptides that cluster the charge and hydrophobic residues may represent a primitive form of microbial pattern-recognition. Incorporating such knowledge in a dendrimeric design therefore presents an attractive approach for developing novel peptide antibiotics.