Glycine Dimerization Motif in the N-terminal Transmembrane Domain of the High Density Lipoprotein Receptor SR-BI Required for Normal Receptor Oligomerization and Lipid Transport
Glycine Dimerization Motif in the N-terminal Transmembrane Domain of the High Density Lipoprotein Receptor SR-BI Required for Normal Receptor Oligomerization and Lipid Transport
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DOI：
10.1074/jbc.m111.229872
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发表时间：
2011-05-27
影响因子：
4.8
通讯作者：
Krieger, Monty
中科院分区：
文献类型：
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作者：
Gaidukov, Leonid;Nager, Andrew R.;Krieger, Monty
B型清道夫受体(SR-BI)是CD36超家族成员之一，是一种低聚高密度脂蛋白(HDLR)受体，介导负协同作用和选择性脂质摄取。我们在SR-BI的N-末端跨膜(N-TM)结构域中发现了一个保守的甘氨酸二聚基序G(15)X(2)G(18)X(3)AX(2)G(25)，其中G(18)X(3)AX(2)G(25)亚基对同质二聚和脂质摄取活性有显著的贡献。SR-BI变异体是通过突变(单个或多个Gly-Gt；Leu替换)或用其他CD36超家族成员的N-TM结构域替换(Croquemort)或缺少(溶酶体完整膜蛋白(LIMP)II)这种甘氨酸基序(嵌合体)而产生的。SR-BI变异体没有表现出表面表达改变(基于抗体结合)或高密度脂蛋白结合。然而，G15L/G18L/G25L三重突变体在细胞表面同源齐聚(>；10倍)和选择性脂质摄取速率(类似于2倍)方面表现出下降。Gly(18)和Gly(25)是SR-BI和SR-BI/Croquemort嵌合体正常摄脂活性所必需的。缺乏甘氨酸基序的SR-BI/LIMP II嵌合体的脂质摄取活性很低，但在第18位和第25位引入甘氨酸可以提高其脂质摄取活性。SR-BI/LIMP II嵌合体介导的脂质摄取速率与受体寡聚程度成正比。因此，SR-BI N-TM结构域上的甘氨酸二聚基序G(18)X(3)AX(2)G(25)对SR-BI的同源齐聚和脂质转运活性有重要作用，但不影响高密度脂蛋白结合的负协同性。与齐聚无关的结合协作性表明，经典的别构作用不参与，负的协作性可能是“晶格效应”(伴随着与相邻受体结合的配体间空间干扰)的结果。
Scavenger receptor class B, type I (SR-BI), a CD36 superfamily member, is an oligomeric high density lipoprotein (HDL) receptor that mediates negatively cooperative HDL binding and selective lipid uptake. We identified in the N-terminal transmembrane (N-TM) domain of SR-BI a conserved glycine dimerization motif, G(15)X(2)G(18)X(3)AX(2)G(25), of which the submotif G(18)X(3)AX(2)G(25) significantly contributes to homodimerization and lipid uptake activity. SR-BI variants were generated by mutations (single or multiple Gly -> Leu substitutions) or by replacing the N-TM domain with those from other CD36 super-family members containing (croquemort) or lacking (lysosomal integral membrane protein (LIMP) II) this glycine motif (chimeras). None of the SR-BI variants exhibited altered surface expression (based on antibody binding) or HDL binding. However, the G15L/G18L/G25L triple mutant exhibited reductions in cell surface homo-oligomerization (> 10-fold) and the rate of selective lipid uptake (similar to 2-fold). Gly(18) and Gly(25) were necessary for normal lipid uptake activity of SR-BI and the SR-BI/croquemort chimera. The lipid uptake activity of the glycine motif-deficient SR-BI/LIMP II chimera was low but could be increased by introducing glycines at positions 18 and 25. The rate of lipid uptake mediated by SR-BI/LIMP II chimeras was proportional to the extent of receptor oligomerization. Thus, the glycine dimerization motif G(18)X(3)AX(2)G(25) in the N-TM domain of SR-BI contributes substantially to the homo-oligomerization and lipid transport activity of SR-BI but does not influence the negative cooperativity of HDL binding. Oligomerization-independent binding cooperativity suggests that classic allostery is not involved and that the negative cooperativity is probably the consequence of a "lattice effect" (interligand steric interference accompanying binding to adjacent receptors).