User:Joseph Lipsick/SRC
From Proteopedia
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The c-src proto-oncogene encodes a protein tyrosine kinase. The v-src oncogene of the Rous sarcoma virus encodes a mutated, activated form of this enzyme. In particular, the virally encoded V-SRC protein lacks the carboxyl-terminus of the normal C-SRC protein. Phosphopeptide mapping and site-directed mutagenesis revealed the importance of two tyrosine (TYR) residues that are critical for the activity and regulation of C-SRC, TYR416 and TYR527. Insertional mutagenesis and comparisons with other proteins revealed the presence of three highly conserved SRC Homology domains, SH1, SH2, and SH3. comprises the catalytic protein kinase. Within SH1 is which must be phosphorylated for full kinase activity. In contrast, when which lies carboxy-terminal to the SH1 domain is phosphorylated, the kinase is inactive. Phosphorylation of TYR527 greatly diminishes phosphorylation of TYR416. Phosphorylation of TYR527 by another protein kinase (CSK) results in the inactivation of C-SRC. Removal of TYR527 by truncation (as in V-SRC) or by substitution with PHE (by site-directed mutagenesis) causes constitutive activation of the kinase. SH2 domains were shown to bind to peptide containing phosphotyrosine. In particular, the domain of C-SRC binds to phospho-TYR527. Although this binding is reversible, the bound state predominates. This bound state prevents the kinase from phosphorylating substrates. Dephosphorylation of TYR527 results in an of the protein structure by release of the SH2 domain. The loop which contains TYR416 and occludes the active site of the SH1 kinase domain is phosphorylated first. phospho-TYR416 alters the conformation of this loop, resulting in a dramatic increase in protein kinase activity. SH3 domains were shown to bind to peptides with multiple adjacent proline residues. The domain of C-SRC binds to the SH2 domain of C-SRC, thereby helping to stabilize the conformation of the entire protein.
from PDB 2SRC
from PDB 1Y57
Notes: The INACTIVE C-SRC structure was solved with an ATP analog [Xu W, et al. Molec Cell 3: 629-38 (1999)]. The ACTIVE C-SRC structure was solved with an inhibitor that alters the conformation of the kinase activation loop even in the absence of phosphorylation of TYR416 [Cowan-Jacob SW, et al. Structure 13: 861-71 (2005)]. These INACTIVE and ACTIVATED C-SRC structures are shown in similar orientations relative to the kinase (SH1) domain to facilitate an understanding of the mechanism of activation. However, an additional amino-terminal domain (SH4) not shown in either structure tethers the protein to the inner plasma membrane via hydrophobic fatty acid chains (myristate and palmitate) that are covalently bound near the amino terminus of C-SRC. This membrane tethering likely provides a fixed attachment point which the remainder of the protein rolls up towards or opens away from during activation. The SH2 domain of C-SRC can bind to phospho-TYR on other proteins (e.g. an activated receptor tyrosine kinase like PDGF-R), thereby opening the C-SRC protein conformation, exposing phospho-TYR527 to protein phosphatases, and resulting in activation of C-SRC.
Review Articles:
Martin GS. The hunting of the Src. Nat Rev Mol Cell Biol 2:467-75 (2001).
Harrison SC. Variations on a Src-like theme. Cell 112:737-40 (2003).
Regulatory Domains and Residues:
