Structural and membrane modifying properties of suzukacillin, a peptide antibiotic related to alamethicin. Part A. Sequence and conformation

Abstract

The primary structure and conformation of the polypeptide antibiotic suzukacillin A are investigated. Suzukacillin A is isolated from the Trichoderma viride strain 1037 and exhibits membrane modifying and lysing properties similar to those of alamethicin. A combined gas chromatographic mass spectrometric analysis of the trifluoroacetylated peptide methyl esters of partial hydrolysates revealed a tentative sequence of 23 residues including 10 2-methylalanines and one phenylalaninol, which shows many fragments known from alamethicin: Ac-Aib-Pro-Val-Aib-Val-Ala-Aib-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-Glu(Pheol)-Gln-OH. All chiral amino acids and phenylalainol have L-configuration. Ultraviolet and infrared spectroscopy, circular dichroism in various solvents and in particular 13C nuclear magnetic resonance have been used for a comparative study of suzukacillin with alamethicin. Suzukacillin has a partially alpha-helical structure and the helix content increases largely from polar to lipophilic solvents. Suzukacillin aggregates more strongly than alamethicin in aqueous medis due to a longer alpha-helical part and higher number of aliphatic residues. A part of the alpha-helix is exceptionally stabilized due to 2-methylalanine residues shielding the peptide bonds from interactions with polar solvents. In lipophilic solvents and lecithin vesicles particularly large temperature induced reductions of the high alpha-helix content are found for alamethicin. Suzukacillin shows similar temperature coefficients in lipophilic media, however, in contrast to alamethicin a more linear change in intensity of the Cotton effects is observed.