Examination of pH dependency and orientation differences of membrane spanning alpha helices carrying a single or pair of buried histidine residues
Examination of pH dependency and orientation differences of membrane spanning alpha helices carrying a single or pair of buried histidine residues
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DOI：
10.1016/j.bbamem.2020.183501
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发表时间：
2021-01-01
影响因子：
3.4
通讯作者：
Koeppe, Roger E., II
中科院分区：
文献类型：
--
作者：
Afrose, Fahmida;Martfeld, Ashley N.;Koeppe, Roger E., II
我们已经采用GWALP 23（乙酰基-GGALWLALALALALALALWLAGA-酰胺）的肽框架来检查具有掩埋的单个或成对组氨酸残基的肽的取向、动力学和pH依赖性。当残基L-8被取代以产生GWALP 23-H-8，乙酰基-GGALWLAH（8）ALALALALWLAGA-酰胺时，H-2标记的核心丙氨酸残基的氘NMR光谱显示在DLPC中或在低pH的DMPC中占据单一跨膜取向的螺旋，但在较高pH或在DOPC的双层中显示多个状态。此外，在GWALP 23框架中的位置8或16处的单个组氨酸对pH敏感。对于DLPC或DMPC的脂质双层中的H-8的去质子化以及对于DOPC中的H-16，在pH 3.5附近观察到滴定点。当残基L-8和L-16都被取代以产生GWALP 23-H-8、H-16时，有趣的是，H-2NMR谱显示没有pH 2-8的滴定依赖性，但双层厚度依赖性取向差异。发现具有H-8和H-16的螺旋在薄的DLPC双层中采用跨膜取向，在DMPC中采用跨膜取向和表面取向的组合，然后在较厚的DPoPC和DOPC脂质双层中完全过渡到表面结合取向。在表面取向中，丙氨酸A7不再适合核心螺旋内。这些结果沿着与以前的研究与不同位置的组氨酸残基表明，脂质疏水厚度是第一个决定因素和pH值的第二个决定因素的螺旋方向，沿着可能的侧链浮潜，当组氨酸残基被纳入到一个脂质膜相关的螺旋的疏水区域。
We have employed the peptide framework of GWALP23 (acetyl-GGALWLALALALALALALWLAGA-amide) to examine the orientation, dynamics and pH dependence of peptides having buried single or pairs of histidine residues. When residue L-8 is substituted to yield GWALP23-H-8, acetyl-GGALWLAH(8)ALALALALALWLAGA-amide, the deuterium NMR spectra of H-2-labeled core alanine residues reveal a helix that occupies a single transmembrane orientation in DLPC, or in DMPC at low pH, yet shows multiple states at higher pH or in bilayers of DOPC. Moreover, a single histidine at position 8 or 16 in the GWALP23 framework is sensitive to pH. Titration points are observed near pH 3.5 for the deprotonation of H-8 in lipid bilayers of DLPC or DMPC, and for H-16 in DOPC. When residues L-8 and L-16 both are substituted to yield GWALP23-H-8,H-16, the H-2 NMR spectra show, interestingly, no titration dependence from pH 2-8, yet bilayer thickness-dependent orientation differences. The helix with H-8 and H-16 is found to adopt a transmembrane orientation in thin bilayers of DLPC, a combination of transmembrane and surface orientations in DMPC, and then a complete transition to a surface bound orientation in the thicker DPoPC and DOPC lipid bilayers. In the surface orientations, alanine A7 no longer fits within the core helix. These results along with previous studies with different locations of histidine residues suggest that lipid hydrophobic thickness is a first determinant and pH a second determinant for the helical orientation, along with possible side-chain snorkeling, when the His residues are incorporated into the hydrophobic region of a lipid membrane-associated helix.