Prosser R S, Luchette P A, Westerman P W, Rozek A, Hancock R E
Department of Chemistry, Kent State University, Kent, Ohio 44242, USA.
Biophys J. 2001 Mar;80(3):1406-16. doi: 10.1016/S0006-3495(01)76113-9.
Oxygen is known to partition with an increasing concentration gradient toward the hydrophobic membrane interior. At partial pressures (P(O2)) of 100 Atm or more, this concentration gradient is sufficient to induce paramagnetic effects that depend sensitively on membrane immersion depth. This effect is demonstrated for the fluorine nucleus by depth-dependent paramagnetic shifts and spin-lattice relaxation rates, using a fluorinated detergent, CF3(CF(2))(5)C(2)H(4)-O-maltose (TFOM), reconstituted into a lipid bilayer model membrane system. To interpret the spin-lattice relaxation rates (R) in terms of a precise immersion depth, two specifically fluorinated cholesterol species (6-fluorocholesterol and 25-fluorocholesterol), whose membrane immersion depths were independently estimated, were studied by (19)F NMR. The paramagnetic relaxation rates, R, of the cholesterol species were then used to parameterize a Gaussian profile that directly relates R to immersion depth z. This same Gaussian curve could then be used to determine the membrane immersion depth of all six fluorinated chain positions of TFOM and of two adjacent residues of specifically fluorinated analogs of the antibacterial peptide indolicidin. The potential of this method for determination of immersion depth and topology of membrane proteins is discussed.
众所周知，氧气会随着浓度梯度增加而向疏水的膜内部扩散。在100个大气压或更高的分压（P(O2)）下，这种浓度梯度足以引发顺磁效应，而该效应敏感地取决于膜的浸入深度。使用一种氟化去污剂CF3(CF(2))(5)C(2)H(4)-O-麦芽糖（TFOM）重构到脂质双层模型膜系统中，通过深度依赖的顺磁位移和自旋晶格弛豫率，对氟原子核的这种效应进行了证明。为了根据精确的浸入深度来解释自旋晶格弛豫率（R），通过19F NMR研究了两种特定氟化的胆固醇种类（6-氟胆固醇和25-氟胆固醇），其膜浸入深度是独立估算的。然后利用胆固醇种类的顺磁弛豫率R来参数化一个高斯分布，该分布直接将R与浸入深度z联系起来。然后可以使用相同的高斯曲线来确定TFOM的所有六个氟化链位置以及抗菌肽吲哚杀菌素的特定氟化类似物的两个相邻残基的膜浸入深度。讨论了该方法在确定膜蛋白浸入深度和拓扑结构方面的潜力。
