Conformational behavior of oxygenated mycobacterial mycolic acids from Mycobacterium bovis BCG
Conformational behavior of oxygenated mycobacterial mycolic acids from Mycobacterium bovis BCG
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DOI：
10.1016/j.bbamem.2007.04.003
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发表时间：
2007-07-01
影响因子：
3.4
通讯作者：
Nakahara, Hiroo
中科院分区：
文献类型：
--
作者：
Villeneuve, Masumi;Kawai, Mizuo;Nakahara, Hiroo
通过对表面压力（pi）和平均分子面积(A)等温线的热力学分析，得到了牛分枝杆菌中氧合霉菌酸(甲氧基霉菌酸（MeO-MA）、酮霉菌酸（Keto-MA）和人工合成的脱氧霉菌酸（deoxo-MA）的Langmuir单层相图。在较低的温度和较低的表面压力下，Keto-和MeO-MAs形成刚性凝聚单层，其中每个MA分子被认为是4链形式，其中三个碳链段由于3羟基脂肪羧酸链和2侧链的弯曲而紧密平行排列。在较高的温度和表面压力下，MeO-MA和deoxo-MA倾向于呈伸展构象，其中3-羟基脂肪羧酸链或多或少呈延伸形式，但Keto-MA保留了原始的4链结构。在不同的pi值和温度下，用椭偏仪原位测量了单层膜的厚度，支持了上述由相图得出的结论。与MeO-MA和脱氧- ma相变相关的焓变化表明，MeO-MA从紧凑构象转变为扩展构象需要更大的能量，可能和部分原因是所涉及的表面甲氧基脱水。通过蒙特卡罗计算得到的分子动力学模型，证实了Langmuir单分子层热力学研究所得的MAs的构象行为。(c) 2007 Elsevier B.V.版权所有
Phase diagrams of Langmuir monolayers of oxygenated mycolic acids, i.e. methoxy mycolic acid (MeO-MA), ketomycolic acid (Keto-MA), and artificially obtained deoxo-mycolic acid (deoxo-MA) from Mycobacterium bovis BCG were obtained by thermodynamic analysis of the surface pressure (pi) vs. average molecular area (A) isotherms. At lower temperatures and lower surface pressures, both Keto- and MeO-MAs formed rigid condensed monolayers where each MA molecule was considered to be in a 4-chain form, in which the three carbon chain segments due to bending of the 3-hydroxy aliphatic carboxylate chain and the 2-side chain were in compact parallel arrangement. At higher temperatures and surface pressures, MeO-MA and deoxo-MA tended to take stretched-out conformations in which the 3-hydroxy aliphatic carboxylate chain was more or less in an extended form, but Keto-MA retained the original 4-chain structure. The thickness measurement of the monolayers in situ by ellipsometry at different pi values and temperatures supported the above conclusions derived from the phase diagrams. The enthalpy changes associated with the phase transitions of MeO-MA and deoxo-MA implied that the MeO-MA needed larger energy to change from a compact conformation to an extended one, possibly and partly due to the dehydration of the methoxy group from water surface involved. Molecular dynamics studies of MA models derived from Monte Carlo calculations were also performed, which confirmed the conformational behavior of MAs suggested by the thermodynamic studies on the Langmuir monolayers. (c) 2007 Elsevier B.V. All rights reserved.