Wang G, Treleaven W D, Cushley R J
Department of Chemistry, Simon Fraser University, Burnaby, BC, Canada.
Biochim Biophys Acta. 1996 Jun 11;1301(3):174-84. doi: 10.1016/0005-2760(96)00037-9.
The segment, YSDELRQRLAARLEALKENG, corresponding to residues 166 to 185 of human serum apolipoprotein A-I, was studied by circular dichroism and NMR spectroscopy in sodium dodecyl sulfate and dodecylphosphocholine micelles. 2-Dimensional NOESY, TOCSY and DQF-COSY spectra of apoA-I(166-185) in perdeuterated sodium dodecyl sulfate (SDS-d25) and dodecylphosphocholine (DPC-d38) micelles were collected at a peptide/SDS (DPC) ratio of 1:40. Similar CD spectra and NOE connectivity patterns were observed for apoA-I(166-185) in SDS and DPC, indicating a similar helical conformation in both. Conformations of apoA-I(166-185) in DPC-d38 micelles, and in SDS-d25 micelles at two pH values, 6.6 and 3.7, were determined using distance geometry calculations. Backbone superposition (N,C alpha,C = O) for an ensemble of twenty-nine structures in DPC at pH 6.0 gave a RMSD of 0.45 +/- 0.09 A for the region D168 to K182, while for all atoms it was 1.60 +/- 0.17 A. In SDS, the ensemble of nineteen structures each at pH 6.6 and 3.7 gave RMSDs of 0.28 +/- 0.07 A and 0.35 +/- 0.10 A, respectively, for the region D168 to K182. RMSD for superposition of all atoms was 1.36 +/- 0.10 A and 1.38 +/- 0.21 A at the respective pH values. In all cases a highly defined class A amphipathic helical structure was found for the region R171 to K182. Since the same structure occurs in micelles with either negatively charged or zwitterionic head groups it strongly suggests a dominant role for hydrophobic interactions in stabilizing the complex. The Y166 aromatic ring is bent back upon the helix axis at the lower pH. NMR determination of pKa values for D168, E169, E179 and E183 in the presence of SDS or DPC indicated a micro-pH at the micellar surface approximately one pH unit higher than the normal residue pKa. SDS interactions with the peptide were examined by collecting 1H NOESY spectra in the presence of protiated SDS. Residues R171, R173, R177, as well as the aromatic ring of Y166, were shown by intermolecular NOE measurements to interact with SDS, hence a key interaction in stabilizing the complex appears to be between interfacial basic side-chains and SDS alkyl chains.
对对应于人血清载脂蛋白A-I第166至185位残基的肽段YSDELRQRLAARLEALKENG，在十二烷基硫酸钠和十二烷基磷酰胆碱胶束中通过圆二色光谱和核磁共振光谱进行了研究。在肽/十二烷基硫酸钠（十二烷基磷酰胆碱）比例为1:40的条件下，收集了载脂蛋白A-I(166 - 185)在全氘代十二烷基硫酸钠（SDS-d25）和十二烷基磷酰胆碱（DPC-d38）胶束中的二维NOESY、TOCSY和DQF-COSY光谱。在SDS和DPC中观察到载脂蛋白A-I(166 - 185)具有相似的圆二色光谱和NOE连接模式，表明两者具有相似的螺旋构象。使用距离几何计算确定了载脂蛋白A-I(166 - 185)在DPC-d38胶束以及在两个pH值（6.6和3.7）的SDS-d25胶束中的构象。在pH 6.0时，DPC中29个结构的集合体的主链叠加（N、Cα、C = O）在D168至K182区域的均方根偏差（RMSD）为0.45±0.09 Å，而对于所有原子，RMSD为1.60±0.17 Å。在SDS中，pH 6.6和3.7时各自19个结构的集合体在D168至K182区域的RMSD分别为0.28±0.07 Å和0.35±0.10 Å。在各自的pH值下，所有原子叠加的RMSD分别为1.36±0.10 Å和1.38±0.21 Å。在所有情况下，R171至K182区域都发现了高度明确的A类两亲性螺旋结构。由于相同的结构出现在带有带负电荷或两性离子头部基团的胶束中，这强烈表明疏水相互作用在稳定复合物中起主导作用。在较低pH值下，Y166芳香环向螺旋轴弯曲。在SDS或DPC存在下对D168、E169、E179和E183的pKa值进行核磁共振测定表明，胶束表面的微pH比正常残基pKa高约一个pH单位。通过在含有质子化SDS的情况下收集1H NOESY光谱来研究SDS与肽的相互作用。分子间NOE测量表明，残基R171、R173、R177以及Y166的芳香环与SDS相互作用，因此稳定复合物的关键相互作用似乎是界面碱性侧链与SDS烷基链之间的相互作用。
