Kistler J, Berriman J, Evans C W, Gruijters W T, Christie D, Corin A, Bullivant S
Department of Cellular & Molecular Biology, University of Auckland, New Zealand.
J Struct Biol. 1990 May;103(3):204-11. doi: 10.1016/1047-8477(90)90038-e.
A 70-kDa membrane protein (MP70) is a component of the lens fiber gap junctions. Its membrane topology and its N-terminal sequence are similar to those of the connexin family of proteins. Some features of MP70 containing fiber gap junctions are, however, distinct from gap junctions in other mammalian tissues: (i) Lens connexons form crystalline arrays only after cleavage of junctional proteins in vitro. These hexagonal arrays have a periodicity of 13.6 nm which is significantly larger than the 8- 9-nm spacing of liver and heart gap junctions. (ii) Lens fiber gap junctions dissociate in low concentrations of nonionic detergent and this provides an avenue to purify MP70 directly from a membrane mixture. Isolated MP70 in the form of 17 S structures has an appearance consistent with connexon pairs. (iii) The C-terminal half of MP70 is cleaved in situ by a lens endogenous calcium-dependent protease. The processed from MP38 remains in the membrane and is abundant in the central region of the lens. A testable hypothesis for MP70 function is presented.
一种70 kDa的膜蛋白（MP70）是晶状体纤维间隙连接的一个组成部分。其膜拓扑结构和N端序列与连接蛋白家族的蛋白质相似。然而，含有MP70的纤维间隙连接的一些特征与其他哺乳动物组织中的间隙连接不同：（i）晶状体连接子仅在体外连接蛋白裂解后形成晶体阵列。这些六边形阵列的周期为13.6 nm，明显大于肝脏和心脏间隙连接的8 - 9 nm间距。（ii）晶状体纤维间隙连接在低浓度非离子去污剂中会解离，这为直接从膜混合物中纯化MP70提供了一条途径。以17 S结构形式分离的MP70的外观与连接子对一致。（iii）MP70的C端一半在体内被晶状体内源性钙依赖性蛋白酶裂解。加工后的MP38保留在膜中，并且在晶状体的中央区域含量丰富。本文提出了一个关于MP70功能的可检验假设。
