Sequences and antimycoplasmic properties of longibrachins LGB II and LGB III, two novel 20-residue peptaibols from Trichoderma longibrachiatum

Longibrachins are members of the class of natural Aib-containing peptides d esignated as peptaibols. Six longibrachins, LGA I-IV and LGB II and III, we re purified from a Trichoderma longibrachiatum strain by a procedure employ ing several chromatography steps including reversed-phase HPLC. The amino a cid sequence determination was based on a combination of liquid secondary i on mass spectrometry (LSIMS) and two-dimensional H-1 and C-13 NMR spectrosc opy. Longibrachins are 20-residue peptaibols with a C-terminal phenylalanin ol and either neutral (LGA; Gln(18)) or acidic (LGB; Glu(18)) character. Lo ngibrachins LGB II and III have novel sequences. Both longibrachins LGA and LGB show significant bactericidal activity against mycoplasmas (Acholeplas ma, Mycoplasma, and Spiroplasma), with minimal inhibitory concentrations in the range 1.56-12.5 muM (3-25 mug/mL), and also perturb the permeability o f membrane bilayers. Longibrachin LGA IV is the most potent of the presentl y 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.