Wälchli Sébastien, Espanel Xavier, Hooft van Huijsduijnen Rob
Serono Pharmaceutical Research Institute, 14, chemin des Aulx, Plan-les-Ouates/Geneva, Switzerland.
Biochem Biophys Res Commun. 2005 Jun 3;331(2):497-502. doi: 10.1016/j.bbrc.2005.03.196.
Sap-1/PTPRH, a receptor protein tyrosine phosphatase (RPTP), is a ubiquitously expressed enzyme that is upregulated in human gastrointestinal cancers. Using both chemical cross-linkers and co-immunoprecipitation we show that overexpressed full-length Sap-1 is present as a stable homodimer. Unlike a number of adhesion RPTPs which have tandem catalytic domains that are involved in dimerization, Sap-1 has a single catalytic domain, and we show that this domain is not required for Sap-1 dimerization, which is mediated instead by the large extracellular and transmembrane domains. Exposing cells that express the receptor to a reducing environment reversibly disrupts the Sap-1 dimer, suggesting that cysteine bonds play a role in dimer formation/stabilization. The switch between Sap-1 dimers and monomers is accompanied by an increase in catalytic activity as judged by its capacity to dephosphorylate and activate c-src, which we identify as a novel substrate for this phosphatase.
Sap-1/PTPRH是一种受体蛋白酪氨酸磷酸酶（RPTP），是一种在人体中广泛表达的酶，在人类胃肠道癌症中上调。我们使用化学交联剂和免疫共沉淀法表明，过表达的全长Sap-1以稳定的同二聚体形式存在。与许多具有参与二聚化的串联催化结构域的黏附RPTP不同，Sap-1具有单个催化结构域，并且我们表明该结构域对于Sap-1二聚化不是必需的，相反，二聚化是由大的细胞外和跨膜结构域介导的。将表达该受体的细胞暴露于还原环境中会可逆地破坏Sap-1二聚体，这表明半胱氨酸键在二聚体形成/稳定中起作用。根据其使c-src去磷酸化并激活的能力判断，Sap-1二聚体和单体之间的转换伴随着催化活性的增加，我们将c-src鉴定为该磷酸酶的一种新底物。
