Edidin M, Zúñiga M C, Sheetz M P
Department of Biology, Johns Hopkins University, Baltimore, MD 21218.
Proc Natl Acad Sci U S A. 1994 Apr 12;91(8):3378-82. doi: 10.1073/pnas.91.8.3378.
The lateral mobility of cell membrane glycoproteins is often restricted by dynamic barriers. These barriers have been detected by measurements of fluorescence photobleaching and recovery (FPR) and barrier-free path (BFP). To define the location and properties of the barriers, we compared the lateral mobility, measured by FPR and BFP, of wild-type class I major histocompatibility complex (MHC) membrane glycoproteins with the lateral mobility of mutant class I MHC glycoproteins truncated in their cytoplasmic domains. Mutants with 0 or 4 residues in the cytoplasmic domain were as mobile as lipid-anchored class I MHC molecules, molecules whose lateral mobility is relatively unrestricted by barriers. In contrast, mobility of class I MHC molecules with 7-residue cytoplasmic domains was as restricted as mobility of class I molecules with full-length, 31-residue cytoplasmic domains. Though some of the difference between the mobilities of mutants with 4- or 0-residue domains and the other class I molecules may be due to differences in the net charge of the cytoplasmic domain, FPR measurements of the mobility of molecules with 7-residue domains show that length of the cytoplasmic domain has an important influence on the lateral mobility. Model calculations suggest that the barriers to lateral mobility are 2-3 nm below the membrane bilayer.
细胞膜糖蛋白的侧向流动性常常受到动态屏障的限制。这些屏障已通过荧光光漂白和恢复（FPR）测量以及无屏障路径（BFP）测量得以检测。为了确定这些屏障的位置和特性，我们比较了野生型I类主要组织相容性复合体（MHC）膜糖蛋白通过FPR和BFP测量得到的侧向流动性与在其胞质结构域被截短的突变型I类MHC糖蛋白的侧向流动性。胞质结构域有0个或4个残基的突变体与脂质锚定的I类MHC分子一样具有流动性，脂质锚定的I类MHC分子的侧向流动性相对不受屏障限制。相比之下，具有7个残基胞质结构域的I类MHC分子的流动性与具有全长31个残基胞质结构域的I类分子的流动性一样受到限制。虽然具有4个或0个残基结构域的突变体与其他I类分子在流动性上的一些差异可能是由于胞质结构域净电荷的不同，但对具有7个残基结构域的分子流动性的FPR测量表明，胞质结构域的长度对侧向流动性有重要影响。模型计算表明，侧向流动性的屏障位于膜双层下方2 - 3纳米处。
