Ramjaun A R, McPherson P S
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
J Biol Chem. 1996 Oct 4;271(40):24856-61. doi: 10.1074/jbc.271.40.24856.
Synaptojanin is an Src homology 3 domain-binding inositol 5-phosphatase that is thought to function in synaptic vesicle endocytosis. It is encoded by a cDNA with two open reading frames separated by an in-frame stop codon. The first open reading frame encodes a 145-kDa form of the protein, whereas a 170-kDa isoform appears to be composed of both open reading frames and contains additional Src homology 3 domain-binding consensus sequences. Here, we demonstrate that the two synaptojanin isoforms are generated by the alternative use of an exon containing the stop codon. Whereas the 145-kDa isoform is highly enriched in adult brain, the 170-kDa isoform is excluded from this tissue and has a widespread distribution in non-neuronal cells. Unlike the 145-kDa isoform, which can be removed from membranes by a low salt wash, the 170-kDa isoform remains membrane-associated, even in the presence of 1 salt. Further, the 170-kDa form, but not the 145-kDa form, can be isolated from membranes as part of a large molecular weight complex. These properties may allow the 170-kDa isoform of synaptojanin to play a unique and perhaps more general role in endocytosis as compared with the 145-kDa isoform.
突触素是一种与Src同源3结构域结合的肌醇5-磷酸酶，被认为在突触小泡内吞作用中发挥作用。它由一个cDNA编码，该cDNA有两个开放阅读框，中间由一个框内终止密码子隔开。第一个开放阅读框编码一种145 kDa的蛋白质形式，而170 kDa的异构体似乎由两个开放阅读框组成，并包含额外的与Src同源3结构域结合的共有序列。在这里，我们证明这两种突触素异构体是通过选择性使用一个含有终止密码子的外显子产生的。145 kDa的异构体在成体大脑中高度富集，而170 kDa的异构体在该组织中不存在，在非神经元细胞中广泛分布。与145 kDa的异构体不同，后者可以通过低盐洗涤从膜上除去，170 kDa的异构体即使在存在1盐的情况下仍与膜结合。此外，170 kDa的形式而不是145 kDa的形式可以作为大分子复合物的一部分从膜上分离出来。与145 kDa的异构体相比，这些特性可能使突触素170 kDa的异构体在内吞作用中发挥独特且可能更普遍的作用。
