Alternative Modes of Tyrosyl Phosphopeptide Binding to a Src Family SH2 Domain: Implications for Regulation of Tyrosine Kinase Activity
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- 作者：John E. Ladbury ; Meike Hensmann ; George Panayotou ; and Iain D. Campbell
- 刊名：Biochemistry
- 出版年：1996
- 出版时间：August 27, 1996
- 年：1996
- 卷：35
- 期：34
- 页码：11062 - 11069
- 全文大小：404K
- 年卷期：v.35,no.34(August 27, 1996)
- ISSN：1520-4995
文摘
Src homology 2 (SH2) domains interact with proteins containingphosphorylated tyrosineresidues and as such play a key role in mediating tyrosine kinasesignal transduction. Determination ofhow these interactions maintain specificity is central to understandingthe mechanism of this intracellularsignal processing. In the Src family tyrosine kinases specificityis enhanced by a form of regulationbased on binding of a phosphotyrosine, pY, and its proximal amino acidsequence from the C-terminusto the SH2 domain of the same protein (autoregulation) or to a similarprotein (homodimeric regulation).Activation of the protein is accomplished by removal of thisregulatory interaction by competition froma "specific" interacting ligand. We adopt the SH2 domain froma member of the Src family, Fyn (whosepredominant physiological role is in initiation of signals from theT-cell receptor complex), to explore thedifferences in structural, thermodynamic, and kinetic determinants ofregulatory and specific interactionsusing tyrosyl phosphopeptides based on the C-terminus and on a putativephysiological interacting speciesfrom the hamster middle-sized tumor antigen. The specific peptideinteracts with micromolar affinity viaembedding the pY and an isoleucine residue (in the pY + 3 position)in two deep pockets. This leads toa large favorable enthalpic contribution to free energy. Theregulatory peptide interacts in the pY pocketwhich forms a pivot for the rest of the molecule which is dynamic.These structural data for the regulatorypeptide are supported by the observation of a more favorable entropicterm and a complex mode of bindingrevealed by kinetic analysis.