Suzukacillin

The third current approach is synthesis of peptide chains as models for the helical peptaibol (Section 8.2) and gramicidin (Section 8.3) ion channels. Considerable work has been carried out in the former area, involving synthesis of Aib-containing small peptides, in order to obtain conformational data applicable to the more complex oligopeptide antibiotics. By working with such fragments it has been possible to obtain valuable X-ray crystal structure information on the helical conformation of ala-methin 246), emerimicin 247), suzukacillin 248), and other members of the peptaibol series. 

Suzukacillin is an antibiotic produced by the same microorganism as alamethicin2 l0 Recent investigations have shown that suzukacillin is a linear peptide with an alamethicin-like sequence of twenty-three amino acids and one phenylalaninol residue1401 Suzukacillin exhibits membrane modifying properties similar to alamethicin2 9 ... 

Suzukacillin peptides (SZ), a peptaibol antibiotic, termed suzukacillin A, was first isolated from the culture broth of the mold Trichoderma viride, strain 1037, exhibiting membrane modifying and lysing properties similar to those of alamethidn. Later, a peptide mixture named SZ-A was obtained by crystallization from crude SZ which was isolated from the culture broth of T. viride, strain 63 C-I. Two major groups of peptides named SZ-A and SZ-B could be separated. The major peptide SZ-A4 (21% of all peptides) has the sequence Ac-Aib-Ala-Aib-Ala-Aib-Ala-Gln-Aib-Lx-Aib -Gly-Aib-Aib-Pro-Vx-Aib-Vx-Gln-Gln-Pheol... 

Remarkably, nearly half of the amino acid components are L-a-amino-isobutyric acid residues (Aib), an amino acid not present in ribosome-manufactured proteins (p. 8). Peptides containing Aib-residues have been recognized to form a-helices particularly readily, an explanation of the pore forming properties of alamethicins and of similar natural and artificial polypeptides. In the natural analogs alanine or valine is found to be replaced by Aib closely related natural compounds are among others, suzukacillin, trichotoxin (mould products), and less similar, a component of bee venom, the 25-peptide mellitin. In the synthesis of peptides containing a-amino-isobutyric acid certain difficulties are encountered due to the poor steric accessibility of the amino—as well as of the carboxyl group. 

Some linear peptides such as the gramicidins A, B, and C, alamethicin, suzukacillin, and trichotoxin A-40 do not act as carriers but they form transmembrane channels across which alkali metal ions can migrate. Just as the carrier cavities, these channels display a hydrophilic interior and a lipophilic exterior, but in contrast to the former they exhibit poor ion selectivity. Since no complete X-ray studies of any of these channel forming agents are available only few facts are known about their conformations. Therefore, they will not be treated in this review. 

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