哺乳动物卵透明带蛋白中C端furin位点存在的意义

Furin Cleavage Site and Proteolytic Processing of Mammalian Zona Pellucida Proteins

根据已克隆的各哺乳动物物种卵透明带(ZP)三种蛋白质的cDNA序列推断,在它们编码的蛋白C端跨膜区上游几乎都存在RXK/RR基序。先前报道存在于许多蛋白C端的这一基序是furin蛋白酶的一个酶切位点。因此,为了阐明各ZP蛋白组份在分泌组装成ZP带时,是否在此furin位点经历了加工处理,以致丢弃它们C端的疏水性跨膜区,几个实验室相继从不同角度用不同方法进行了探讨。从目前的大多数实验结果来看,三个ZP组成蛋白分泌前在它们C端跨膜区上游的furin位点被切割的证据是充分的。当然也有相反的实验证明,即各ZP蛋白不经历此位点切割也能被分泌并进行ZP组装和扩张。对此截然相反的研究结果,一个可能的解释,也许是重组小鼠ZP3中分别选用了不同的表位标签和插入位置以及使用了不同的转染细胞株。

The zona pellucida (ZP) matrix surrounding mammalian eggs consists of three major sulfated glycoproteins-ZP1, ZP2, and ZP3. Almost all cloned ZP protein sequences contain a well-conserved cleavage site ( Arg - X - Lys / Arg - Arg motif ) upatream of the carboxyl - terminal transmembrane domain , which suggests proteolytic processing by a furin endoprotease. To determine whether three ZP proteins are cleaved at the consensus furin site prior to secretion or incorporation into the ZP, several laboratories explored processing events in the carboxyl-terminal region by using different methods recently. Most experimental results support the hypothesis that formation of the ZP matrix involves regulated proteolysis by a furin endoprotease, but an opposite conclusion was reported in another paper, that is, this cleavage is not prerequisite event for mouse ZP3 protein secretion. The reason for this discrepancy needs to be further explained, but it might be, at least in part, due to the different epitope-tags and different positions inserted in the recombinant protein and the different cell lines employed for the transfection studies.