通过2H-NMR研究磷脂酰丝氨酸头部基团和酰基链结构及动力学的pH依赖性。

The pH dependence of headgroup and acyl chain structure and dynamics of phosphatidylserine, studied by 2H-NMR.

作者信息

de Kroon A I, Timmermans J W, Killian J A, de Kruijff B

机构信息

Centre for Biomembranes and Lipid Enzymology, University of Utrecht, The Netherlands.

出版信息

Chem Phys Lipids. 1990 Apr;54(1):33-42. doi: 10.1016/0009-3084(90)90057-x.

DOI:10.1016/0009-3084(90)90057-x

PMID:2163285

Abstract

By varying the pH, the influence of the ionization degree on the structure and dynamics of aqueous dispersions of 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) was studied, using 2H-NMR methods. For this purpose DOPS was synthesized with deuterium labels incorporated either stereospecifically at the beta-position of the serine headgroup ([2-2H]DOPS) or at the 11-position of both acyl chains ([11,11-2H2]DOPS), allowing the effects of pH on headgroup and acyl chains to be measured in parallel. A large scale synthesis procedure of stereospecific 1,2-dioleoyl-sn-glycero-3-phospho-[2-2H]-L- serine is described. The quadrupolar splitting (delta nu q) of [2-2H]DOPS is shown to be a sensitive sensor for the degree of protonation of the molecule. Whereas the delta nu q of [2-2H]DOPS decreases upon lowering the pH, that of [11,11-2H2]DOPS gradually increases, indicating an increase in acyl chain ordering. In the pH range below the pKa value, DOPS exhibits a temperature-dependent bilayer to hexagonal HII phase transition, apparent from the 31P-NMR spectra and the occurrence of a second component in the [11,11-2H2]DOPS 2H-NMR spectrum, with a much smaller delta nu q. The HII phase component in spectra from [2-2H]DOPS coincides with the isotropic position and has no defined delta nu q. In the bilayer organization delta nu q and spin-lattice relaxation time (T1) values for the acyl chain deuterated DOPS are similar to those obtained for other lipid systems. In contrast the PS headgroup region displays a relatively rigid structure as evidenced by a large delta nu q and very small T1 values. Upon adopting the HII phase the T1 values of the acyl chain deuterons are hardly affected. The uniqueness of the PS headgroup with respect to structure and motional properties is reinforced by the occurrence of a T1 minimum at 45 degrees C in the measurement of the temperature dependence of T1 for [2-2H]DOPS in the hexagonal HII configuration. Quantitative analysis yields a correlation time (tau c) for the motions determining T1 under these conditions, of 3.45 ns.

摘要

通过改变pH值，使用2H-NMR方法研究了电离度对1,2-二油酰基-sn-甘油-3-磷酸-L-丝氨酸（DOPS）水分散体结构和动力学的影响。为此，合成了在丝氨酸头部基团的β位立体定向掺入氘标记（[2-2H]DOPS）或在两条酰基链的11位掺入氘标记（[11,11-2H2]DOPS）的DOPS，从而能够并行测量pH值对头部基团和酰基链的影响。描述了立体定向1,2-二油酰基-sn-甘油-3-磷酸-[2-2H]-L-丝氨酸的大规模合成方法。结果表明，[2-2H]DOPS的四极分裂（δνq）是分子质子化程度的灵敏传感器。随着pH值降低，[2-2H]DOPS的δνq减小，而[11,11-2H2]DOPS的δνq逐渐增大，表明酰基链有序性增加。在低于pKa值的pH范围内，DOPS表现出温度依赖性的双层到六方HII相转变，这从31P-NMR光谱以及[11,11-2H2]DOPS 2H-NMR光谱中出现的第二个成分可以明显看出，其δνq要小得多。[2-2H]DOPS光谱中的HII相成分与各向同性位置重合，没有确定的δνq。在双层结构中，酰基链氘代DOPS的δνq和自旋晶格弛豫时间（T1）值与其他脂质体系获得的值相似。相比之下，PS头部基团区域显示出相对刚性的结构，这由较大的δνq和非常小的T1值证明。在采用HII相时，酰基链氘核的T1值几乎不受影响。在六方HII构型下测量[2-2H]DOPS的T1温度依赖性时，在45℃出现T1最小值，这进一步证明了PS头部基团在结构和运动性质方面的独特性。定量分析得出在这些条件下决定T1的运动的相关时间（τc）为3.45 ns。