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1 Wiadomości Chemiczne

1 2007

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w słowach kluczowych: distribution of cations in the gramicidin dimers

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Strukturalne zagadki kompleksowanych gramicydyn w ich kryształach

Główka M.L., Olczak A., Bojarska J., Szczesio M.

Wiadomości Chemiczne

2007

[Z] 61, 3-4

167-187

Gramicidin D (gD) is a naturally occurring mixture of six linear pentadecapeptides produced by Bacillus brevis species in soil, which exhibit significant antibacterial activity against all Gram+ bacteria. The peptides are modified at both ends and the six forms differ at 1st (Val or Ile) and 11th (Trp, Phe or Tyr) positions. The most populated gramicidin A (VgA) has a sequence CH(O)-Val_1-Gly-Ala-D-Leu-Ala-D-Val-Val-D-Val-Trp-D-Leu-Trp_11-D-Leu-Trp-D-Leu-Trp-NHCH_2CH_2OH. Gramicidin was isolated in 1939 and its sequence was determined five years later. First models of its secondary structure based on helical conformation were proposed in 1971-1974 explaining channel-like properties of the peptide. Despite over 60 years of studies on gramicidin, there are still numerous unans-wered questions concerning its structure and functioning. Even fundamental issues of dimers type and handedness of helices in the gramicidin channel formed by the peptide in the bacterial cell membranes are not univocally accepted. After refining several crystal structures of gramicidin D complexes with alkali metal salts, we have at hands not only more facts concerning double-stranded antiparallel gramicidin dimers, but also new puzzled observations due to very high reso-lution data collected. These, among others, include visible asymmetry of cations' sites and occupations in the gramicidin channels, as well as specific arrangement of heterodimers in the crystals. The paper describes these interesting features of the complexed gramicidin structure and proposes some new explanations.