Paré C, Lafleur M, Liu F, Lewis R N, McElhaney R N
Département de Chimie, Université de Montréal, Québec, Canada.
Biochim Biophys Acta. 2001 Mar 9;1511(1):60-73. doi: 10.1016/s0005-2736(00)00382-5.
We have studied the effects of the incorporation of the alpha-helical transmembrane peptides Ac-K(2)-L(24)-K(2)-amide (L(24)) and Ac-K(2)-(L-A)(12)-K(2)-amide ((LA)(12)) on the thermotropic phase behavior of 1,2-dipalmitoyl-d(62)-sn-glycero-3-phosphocholine (DPPC-d(62)) and 1-palmitoyl-d(31)-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d(31)) lipid bilayer model membranes by differential scanning calorimetry (DSC) and the conformational and orientational order of the phospholipid chains by Fourier transform infrared (FTIR) spectroscopy and (2)H nuclear magnetic resonance ((2)H-NMR) spectroscopy, respectively. Our DSC and FTIR spectroscopic studies indicate that the peptides L(24) and (LA)(12) both decrease the temperature and enthalpy of the gel/liquid-crystalline phase transition of DPPC-d(62) bilayers, with (LA)(12) having the greater effect in this regard. An examination of the frequencies of the CH(2) and CD(2) symmetric stretching bands of the infrared spectra of liquid-crystalline states of the peptide-free and peptide-containing DPPC-d(62) and POPC-d(31) samples, and a comparison with the orientational order as measured by (2)H-NMR spectroscopy as well as with the chain order as measured by electron spin resonance spectroscopy, lead us to conclude that the CH(2) (or CD(2)) stretching frequencies of lipid hydrocarbon chains are not a reliable measure of chain conformational order in lipid bilayers containing significant amounts of peptides or other lipophilic inclusions. In contrast, the results of our (2)H-NMR spectroscopic studies present a consistent picture in which both L(24) and (LA)(12) increased in a similar way the time-averaged orientational order of the lipid chains of their liquid-crystalline lipid bilayer hosts. The comparison of the effects L(24) and (LA)(12) on phosphatidylcholine bilayers indicates that the gel-to-liquid-crystalline phase transition appears to be more sensitive to small changes in transmembrane peptide surface topology than hydrocarbon carbon chain orientational order in the liquid-crystalline state.
我们通过差示扫描量热法（DSC）研究了α-螺旋跨膜肽Ac-K(2)-L(24)-K(2)-酰胺（L(24)）和Ac-K(2)-(L-A)(12)-K(2)-酰胺（(LA)(12)）的掺入对1,2-二棕榈酰-d(62)-sn-甘油-3-磷酸胆碱（DPPC-d(62)）和1-棕榈酰-d(31)-2-油酰-sn-甘油-3-磷酸胆碱（POPC-d(31)）脂质双层模型膜热致相行为的影响，并分别通过傅里叶变换红外（FTIR）光谱和(2)H核磁共振（(2)H-NMR）光谱研究了磷脂链的构象和取向有序性。我们的DSC和FTIR光谱研究表明，肽L(24)和(LA)(12)均降低了DPPC-d(62)双层凝胶/液晶相转变的温度和焓，在这方面(LA)(12)的影响更大。对不含肽和含肽的DPPC-d(62)和POPC-d(31)样品液晶态红外光谱中CH(2)和CD(2)对称伸缩带频率进行检查，并与通过(2)H-NMR光谱测量的取向有序性以及通过电子自旋共振光谱测量的链有序性进行比较，我们得出结论，在含有大量肽或其他亲脂性内含物的脂质双层中，脂质烃链的CH(2)（或CD(2)）伸缩频率不是链构象有序性的可靠度量。相比之下，我们的(2)H-NMR光谱研究结果呈现出一致的情况，即L(24)和(LA)(12)均以类似方式增加了其液晶脂质双层宿主中脂质链的时间平均取向有序性。L(24)和(LA)(12)对磷脂酰胆碱双层影响的比较表明，凝胶-液晶相转变似乎比液晶态下的烃碳链取向有序性对跨膜肽表面拓扑结构的微小变化更敏感。
