Sequences and Antimycoplasmic Properties of Longibrachins LGB II and LGB III, Two Novel 20-Residue Peptaibols fromTrichodermalongibrachiatum

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Abstract
Longibrachins are members of the class of natural Aib-containing peptides designated as peptaibols. Six longibrachins, LGA I−IV and LGB II and III, were purified from a Trichoderma longibrachiatum strain by a procedure employing several chromatography steps including reversed-phase HPLC. The amino acid sequence determination was based on a combination of liquid secondary ion mass spectrometry (LSIMS) and two-dimensional 1H and 13C NMR spectroscopy. Longibrachins are 20-residue peptaibols with a C-terminal phenylalaninol and either neutral (LGA; Gln18) or acidic (LGB; Glu18) character. Longibrachins LGB II and III have novel sequences. Both longibrachins LGA and LGB show significant bactericidal activity against mycoplasmas (Acholeplasma,Mycoplasma, and Spiroplasma), with minimal inhibitory concentrations in the range 1.56−12.5 μM (3−25 μg/mL), and also perturb the permeability of membrane bilayers. Longibrachin LGA IV is the most potent of the presently known 18−20-residue peptaibols. The antimicrobial and membrane-perturbing properties of longibrachins, which are described here for the first time, were shown to be correlated.