Marked increase in membranolytic selectivity of novel cyclic tachyplesins constrained with an antiparallel two-beta strand cystine knot framework

We have developed a highly constrained 18-residue cyclic peptide template b ased on the antimicrobial peptide tachyplesin-1 that features an end-to-end peptide backbone and a cystine knot-like motif with three evenly spaced di sulfide bonds to cross-brace the antiparallel beta-strands and to approxima te an amphiphatic "beta-tile"-like structure. Six beta-tile analogs were pr epared to correlate different topological patterns with membranolytic speci ficity. Their conformations and antimicrobial and hemolytic activities were compared with tachyplesin-1 and the recently discovered Rhesus monkey thet a defensin (RTD) which contains similar beta-tile structural elements. The beta-tile peptides and RTD retained broad spectrum antimicrobial activities . In general, they were less active than tachyplesin-1 in 10 tested organis ms but their activity increased under high-salt (100 mM NaCl) rather than i n low-salt conditions, The beta-tile peptides are highly nontoxic to human erythrocytes with EC25 ranging from 600 to 4000 mu M. Collectively, our res ults show that the design of a highly rigid peptide template is useful for further analog study to dissociate antimicrobial activity from cytotoxicity which would be helpful in discovering clinical applications for peptide an tibiotics. (C) 2000 Academic Press.