Ca(2+)-induced changes of surfactin conformation: a FTIR and circular dichroism study.
Previous NMR studies on surfactin proposed two gamma or beta-turn-containing conformers while recent CD studies described beta-sheets and alpha-helices in surfactin. Since these data were not obtained in the same conditions, the conformation of surfactin was reinvestigated by FTIR spectroscopy, a diagnostic method for beta-sheets. In trifluoroethanol, the FTIR spectra of surfactin and its diester are compatible with gamma and/or beta-turn(s) and the differences in their CD spectra show the importance of the Glu(1) and Asp(5) COOH groups in stabilizing the lipopeptide conformation. The calcium-induced spectral changes of both lipopeptides suggest a first binding of the divalent ions to the surfactin COOH groups (until calcium-lipopeptide mole ratio reached 1) followed by bulk conformational changes (at higher mole ratios). In Tris buffer at pH 8.5, the FTIR amide I band shape, without the typical 1610-1628 and 1675-1695 cm(-1) bands, ascertains the absence of beta-sheets.
Department of Organic Chemistry, Eötvös Loránd University, Budapest, H-1518, Hungary.
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Vass
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Besson
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Majer
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Volpon
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Hollósi
D001426:Bacterial Proteins / Q000737:chemistry / Q000187:drug effects*; D002118:Calcium / Q000494:pharmacology*; D002942:Circular Dichroism; D055666:Lipopeptides; D010456:Peptides, Cyclic; D011487:Protein Conformation; D017550:Spectroscopy, Fourier Transform Infrared
D001426:Bacterial Proteins; D055666:Lipopeptides; D010456:Peptides, Cyclic; C009365:surfactin peptide; D002118:Calcium