Aibellin

Aibellin is a 20-residue peptide antibiotic that has been isolated from the fungus Verticimonosporium ellipticum. Sequence-specific assignment of the 1H- and 13C-NMR signals of aibellin in a methanol solution was achieved by using the two-dimensional NMR technique. Furthermore, its secondary structure was characterized by circular dichroism (CD) and NOESY spectra. The observed NOEs, 3JNHC alpha H coupling constants and amide hydrogen-deuterium (H-D) exchange rates show that the peptide consisted of two alpha-helices and a bent structure around a Pro-14 residue.

Aibellin was administered in feed to goats (16 to 18 kg of BW) for 12 d. At 80 mg/d, the molar percentage of propionate in rumen fluid increased significantly in 8 d, and the effect lasted for as long as 10 d after administration ceased. Total VFA concentration, protozoa numbers, and NDF digestibility were not depressed significantly at this dosage but were reduced at 100 mg/d with little further increase in the molar percentage of propionate. Therefore, the optimal dosage of aibellin was 80 mg/d under our experimental conditions. In contrast, monensin (30 mg/d) and gramicidin D (60 mg/d) decreased total VFA concentration and protozoa numbers when supplemented to obtain molar percentages of propionate comparable to 80 mg/d of aibellin. From these results, aibellin may be easier and safer to use than monensin and gramicidin D to modify rumen fermentation.

A new peptide antibiotic, aibellin, that had the efficiency enhancing activity on rumen fermentation, was isolated from the culture broth of the fungus, Verticimonosporium ellipticum D1528, and its primary structure was elucidated from spectrometric analysis and chemical degradation. Aibellin is a 20-residue peptaibol, and it has a unique structural feature in the novel C-terminal amino alcohol. Moreover, aibellin is the first peptaibol that possesses two acidic amino acids in the C-terminal region and a Phe residue in the middle of the sequence.