SYNTHESIS AND ANTIBACTERIAL ACTION OF CECROPIN AND PROLINE-ARGININE-RICH PEPTIDES FROM PIG INTESTINE

Two antimicrobial peptides, cecropin P1 (CP1), with a C-terminal carbo xyl group, and PR-39, with an amidated C-terminus, are found in the sm all intestine of the pig. Each is active against both Grampositive and Gram-negative bacteria. We have synthesized these peptides and severa l analogs, including the D-enantiomers and the retro sequences, each w ith a free or acetylated amino terminus. The CP1 amide was also prepar ed. The retro CPI peptides were much less active than the parent CP1 p eptide, confirming the importance of sequence or the amide bond and he lix dipole direction, and the N-alpha-acetyl peptides were also less a ctive, indicating that a free amino terminus is essential for high act ivity. The ratio of the lethal concentration of L/D isomers of CP1 is less than 1 for Gram-negative, but greater than 1 for Gram-positive ba cteria. PR-39 showed no significant chiral selectivity toward Escheric hia coli, Bacillus subtilis and Streptococcus pyogenes, but the L/D ra tio was high for Pseudomonas aeruginosa (66), and very high for Staphy lococcus aureus (>1000). In the latter case the lethal concentration f or the D-isomer was 0.57 mu M, whereas this organism was quite resista nt to the L-isomer (> 600 mu M). Thus the enantiomers of CP1 and PR-39 are not equally active for all species. In a plate assay with a very small log-phase inoculum of Staph. aureus, D-PR-39 produced a clear zo ne of killing surrounded by a zone of stimulated growth. After prolong ed incubation the two zones became one clear zone. Addition of D-PR-39 to the wells of a dense turbid plate of growing cells showed a cleare d zone for each of the test organisms, indicating that PR-39 lyses the bacteria rather than simply inhibiting their multiplication. (C) Munk sgaard 1997.