Phospholipase C- (cid:103) 1 Interacts with Conserved Phosphotyrosyl Residues in the Linker Region of Syk and Is a Substrate for Syk
Phospholipase C- (cid:103) 1 Interacts with Conserved Phosphotyrosyl Residues in the Linker Region of Syk and Is a Substrate for Syk
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抗原受体连接激活蛋白酪氨酸激酶和异构体。含有PLC- (cid:103) 1的C端src -同源2 [SH2(C)]结构域的谷胱甘肽S -转移酶融合蛋白与酪氨酸磷酸化的Syk结合。从抗原受体激活的B细胞中分离的Syk使PLC- (cid:103) 1在Tyr-771和关键调控残基Tyr-783上磷酸化，而来自相同B细胞的Lyn仅在Tyr-771上磷酸化PLC- (cid:103) 1。Syk磷酸化PLC- (cid:103) 1的能力需要抗原受体连接，而Lyn则具有组成性活性。mCD8-Syk cDNA构建物可在COS细胞中表达为酪氨酸磷酸化嵌合蛋白酪氨酸激酶，在体外被PLC- (cid:103) 1 SH2(C)识别，并在体内诱导内源性PLC- (cid:103) 1酪氨酸磷酸化。在mCD8-Syk中Syk自磷酸化位点替换Tyr-525和Tyr-526可显著降低激酶活性，并降低该变异嵌合体与PLC-的结合（cid:103）。
Antigen receptor ligation on activates protein tyrosine kinases and isoforms. Glutathione S -transferase fusion proteins containing the C-terminal Src-homology 2 [SH2(C)] domain of PLC- (cid:103) 1 bound to tyrosyl phosphorylated Syk. Syk isolated from antigen receptor-activated B cells phosphorylated PLC- (cid:103) 1 on Tyr-771 and the key regulatory residue Tyr-783 in vitro, whereas Lyn from the same B cells phosphorylated PLC- (cid:103) 1 only on Tyr-771. The ability of Syk to phosphorylate PLC- (cid:103) 1 required antigen receptor ligation, while Lyn was constitutively active. An mCD8-Syk cDNA construct could be expressed as a tyrosyl-phosphorylated chimeric protein tyrosine kinase in COS cells, was recognized by PLC- (cid:103) 1 SH2(C) in vitro, and induced tyrosyl phosphorylation of endogenous PLC- (cid:103) 1 in vivo. Substitution of Tyr-525 and Tyr-526 at the autophosphorylation site of Syk in mCD8-Syk substantially reduced the kinase activity and the binding of this variant chimera to PLC- (cid:103)