Asuncion-Punzalan E, Kachel K, London E
Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215, USA.
Biochemistry. 1998 Mar 31;37(13):4603-11. doi: 10.1021/bi9726234.
To understand the relationship between the chemical structure of polar molecules and their membrane location, the behavior of dansyl (dimethylaminonaphthalenesulfonyl) and related polar fluorescent probes was examined. The depth of these probes in lipid bilayers was determined by parallax analysis of fluorescence quenching [Chattopadhyay and London (1987) Biochemistry 26, 39-45; Abrams & London, Biochemistry (1993) 32, 10826-10831]. Quenching was measured for dansyl groups: (1) attached to the polar headgroup of PE, (2) linked to an alkyl chain, (3) attached to the end of a fatty acyl chain, and (4) attached to the polar headgroup of PE via a spacer group. In all cases, the dansyl probes located in the polar headgroup region, 19-21 A from the bilayer center. This shows the dansyl group has a strong tendency to seek a shallow location in the polar headgroup region. The only exception to this pattern was in the case of a dialkylated dansyl, for which two populations were observed. One population was at the polar headgroup level, but the second was deeply buried in the acyl chain region. To see if the polar sulfonamide group of dansyl influences depth, a structurally related probe substituting a thiocarbamoyl linkage, dimethylaminonaphthalenethiocarbamoyl (dantyl)-labeled PE, was synthesized. Dantyl groups were located deeper than dansyl groups, 13-16 A from the bilayer center. There was an even more dramatic difference in depth between dansyl and mansyl (methylanilinonaphthalenesulfonyl) derivatives. Mansyl probes, which have an extra phenyl group relative to dansyl, were found to locate deeply within the acyl chain region of the bilayer (6-7 A from the bilayer center) when attached to the polar headgroup of PE. Thus, the membrane location of polar groups depends strongly on the details of their chemical structure, and it is possible for a polar group to locate both at shallow and deep locations. These results suggest the energy to bury a polar moiety in the hydrophobic part of the bilayer is not prohibitively high. This contrasts to the behavior of charged groups, which appear to be restricted to shallow locations in membranes. In this report, the effect of populations at two different depths on the parallax analysis is also considered.
为了理解极性分子的化学结构与其在膜中位置的关系，我们研究了丹磺酰基（二甲基氨基萘磺酰基）及相关极性荧光探针的行为。这些探针在脂质双层中的深度通过荧光猝灭的视差分析来确定[Chattopadhyay和London（1987年），《生物化学》26卷，39 - 45页；Abrams和London，《生物化学》（1993年）32卷，10826 - 10831页]。我们测量了丹磺酰基的猝灭情况：（1）连接到磷脂酰乙醇胺（PE）的极性头部基团；（2）连接到烷基链；（3）连接到脂肪酰链的末端；（4）通过间隔基团连接到PE 的极性头部基团。在所有情况下，丹磺酰探针都位于极性头部基团区域，距离双层中心19 - 21埃。这表明丹磺酰基团有强烈的倾向在极性头部基团区域寻找较浅的位置。这种模式唯一的例外是二烷基化丹磺酰基的情况，在这种情况下观察到了两种分布。一种分布在极性头部基团水平，但第二种分布深埋在酰链区域。为了探究丹磺酰基的极性磺酰胺基团是否影响深度，我们合成了一种结构相关的探针，用硫代氨基甲酰基连接取代，即二甲基氨基萘硫代甲酰基（丹硫酰基）标记的PE。丹硫酰基团的位置比丹磺酰基团更深，距离双层中心13 - 16埃。丹磺酰基和甲磺酰基（甲基苯胺基萘磺酰基）衍生物在深度上有更显著的差异。当连接到PE的极性头部基团时，相对于丹磺酰基有一个额外苯基的甲磺酰基探针被发现深埋在双层的酰链区域内（距离双层中心6 - 7埃）。因此，极性基团在膜中的位置强烈依赖于其化学结构的细节，并且一个极性基团有可能位于浅部和深部位置。这些结果表明将一个极性部分埋入双层疏水部分的能量并非高得令人望而却步。这与带电基团的行为形成对比，带电基团似乎被限制在膜中的浅部位置。在本报告中，还考虑了两种不同深度的分布对视差分析的影响。
