Structure and Dynamics of Surfactin Studied by NMR in Micellar Media

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• 作者：Pascale Tsan ; Laurent Volpon ; Franç ; oise Besson ; Jean-Marc Lancelin
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：February 21, 2007
• 年：2007
• 卷：129
• 期：7
• 页码：1968 - 1977
• 全文大小：352K
• 年卷期：v.129,no.7(February 21, 2007)
• ISSN：1520-5126

文摘

The NMR structure of the cyclic lipopeptide surfactin from Bacillus subtilis was determined insodium dodecyl sulfate (SDS) micellar solution. The two negatively charged side chains of surfactin forma polar head opposite to most hydrophobic side chains, accounting for its amphiphilic nature and its strongsurfactant properties. Disorder was observed around the fatty acid chain, and ¹⁵N relaxation studies wereperformed to investigate whether it originates from a dynamic phenomenon. A very large exchangecontribution to transverse relaxation rate R₂ was effectively observed in this region, indicating slowconformational exchange. Temperature variation and Carr-Purcell-Meiboom-Gill (CPMG) delay variationrelaxation studies provided an estimation of the apparent activation energy around 35-43 kJ·mol^-1 andan exchange rate of about 200 ms^-1 for this conformational exchange. ¹⁵N relaxation parameters werealso recorded in dodecylphosphocholine (DPC) micelles and DMSO. Similar chemical exchange aroundthe fatty acid was found in DPC but not in DMSO, which demonstrates that this phenomenon only occursin micellar media. Consequently, it may either reflect the disorder observed in our structures determinedin SDS or originate from an interaction of the lipopeptide with the detergent, which would be qualitativelysimilar with an anionic (SDS) or a zwitterionic (DPC) detergent. These structural and dynamics results onsurfactin are the first NMR characterization of a lipopeptide incorporated in micelles. Moreover, they providea model of surfactin determined in a more biomimetic environment than an organic solvent, which couldbe useful for understanding the molecular mechanism of its biological activity.