Determination of N- and C-terminal borders of the transmembrane domain of integrin subunits
Determination of N- and C-terminal borders of the transmembrane domain of integrin subunits
复制标题
DOI：
10.1074/jbc.m400771200
复制
发表时间：
2004-05-14
影响因子：
4.8
通讯作者：
Johansson, S
中科院分区：
文献类型：
--
作者：
Stefansson, A;Armulik, A;Johansson, S
先前对人整联蛋白亚基膜-细胞质间相的研究表明，在没有相互作用蛋白的情况下，亚基 α(2)、α(5)、β(1) 和 β(2) 中的保守赖氨酸嵌入质膜中（Armulik, A.、Nilsson, I.、von Heijne, G. 和 Johansson, S. (1999) in J. Biol. Chem. 274、37030-37034）。使用糖基化作图技术，我们在这里发现α（10）和β（8）这两个与膜近端区域的整合素共有序列显着偏离的亚基，被发现在脂质双层中的相似位置具有保守的赖氨酸。因此，跨膜 (TM) 结构域 C 末端的这种组织似乎对于所有 24 个整联蛋白亚基都是通用的。此外，我们还确定了α(2)、α(5)、α(10)、β(1)和β(8)亚基的TM结构域的N端边界。亚基 beta(8) 的 TM 结构域长 22 个氨基酸，第二个碱性残基 (Arg(684)) 位于外质侧膜内，而其他亚基的脂质嵌入结构域更长，从 25 个 (α(2)) 到 29 个氨基酸 (α(10)) 不等。这些数字表明所分析的整联蛋白（β(8) 除外）的 TM 区域将在膜中倾斜或弯曲。通过跨膜构象变化的整合素信号传导可能涉及与保守赖氨酸相邻的片段位置的改变。为了测试所提出的信号传导“活塞”模型，我们通过用 Lys-Lys 替换 Lys-Leu，迫使 alpha(5) 和 beta(1) TM 结构域 C 末端的该区域离开膜进入细胞质。发现该突变不会改变 TM 结构域 N 末端在膜中的位置，表明 TM 结构域不会像活塞一样移动。相反，这种转变会导致TM α螺旋更短，因此倾斜或弯曲更少。
Previous studies on the membrane-cytoplasm interphase of human integrin subunits have shown that a conserved lysine in subunits alpha(2), alpha(5), beta(1), and beta(2) is embedded in the plasma membrane in the absence of interacting proteins (Armulik, A., Nilsson, I., von Heijne, G., and Johansson, S. (1999) in J. Biol. Chem. 274, 37030-37034). Using a glycosylation mapping technique, we here show that alpha(10) and beta(8), two subunits that deviate significantly from the integrin consensus sequences in the membrane-proximal region, were found to have the conserved lysine at a similar position in the lipid bilayer. Thus, this organization at the C-terminal end of the transmembrane (TM) domain seems likely to be general for all 24 integrin subunits. Furthermore, we have determined the N-terminal border of the TM domains of the alpha(2), alpha(5), alpha(10), beta(1), and beta(8) subunits. The TM domain of subunit beta(8) is found to be 22 amino acids long, with a second basic residue (Arg(684)) positioned just inside the membrane at the exoplasmic side, whereas the lipid-embedded domains of the other subunits are longer, varying from 25 (alpha(2)) to 29 amino acids (alpha(10)). These numbers implicate that the TM region of the analyzed integrins (except beta(8)) would be tilted or bent in the membrane. Integrin signaling by transmembrane conformational change may involve alteration of the position of the segment adjacent to the conserved lysine. To test the proposed "piston" model for signaling, we forced this region at the C-terminal end of the alpha(5) and beta(1) TM domains out of the membrane into the cytosol by replacing Lys-Leu with Lys-Lys. The mutation was found to not alter the position of the N-terminal end of the TM domain in the membrane, indicating that the TM domain is not moving as a piston. Instead the shift results in a shorter and therefore less tilted or bent TM alpha-helix.