A Myristoyl Binding Site in the SH3 Domain Modulates c-Src Membrane Anchoring

Abstract

The c-Src oncogene is anchored to the cytoplasmic membrane through its N-terminal myristoylated SH4 domain. This domain is part of an intramolecular fuzzy complex with the SH3 and Unique domains. Here we show that the N-terminal myristoyl group binds to the SH3 domain in the proximity of the RT loop, when Src is not anchored to a lipid membrane. Residues in the so-called Unique Lipid Binding Region modulate this interaction. In the presence of lipids, the myristoyl group is released from the SH3 domain and inserts into the lipid membrane. The fuzzy complex with the SH4 and Unique domains is retained in the membrane-bound form, placing the SH3 domain close to the membrane surface and restricting its orientation. The apparent affinity of myristoylated proteins containing the SH4, Unique, and SH3 domains is modulated by these intramolecular interactions, suggesting a mechanism linking c-Src activation and membrane anchoring.

Src Family Tyrosine Kinases in Intestinal Homeostasis, Regeneration and Tumorigenesis

“…Nevertheless, Moasser et al reported that Src dimerisation also involves the interaction of the myristoylated N-terminal region with the kinase domain pocket in trans [ 20 ]. Surprisingly, Pons et al discovered an additional myristoyl binding site in Src-SH3, that contributes to Src membrane anchoring [ 24 ]. Interestingly this interaction is modulated by the fuzzy complex contained in the UD, suggesting a mechanism linking Src activation and membrane anchoring.…”

N-myristoylation: from cell biology to translational medicine

“…Many proteins require assembly for maturity and function, and some evidence indicates that N-myristoylation drives the aggregation of proteins in some cases [ 37 ]. Spassov et al reported that Src dimerization is mediated by the myristoylated N-terminal region of one partner interacting with the hydrophobic kinase domain of its counterpart [ 38 , 39 ]. Both Y419 autophosphorylation and dimerization are codependent and activate Src kinases (Fig.…”

The disordered boundary of the cell: emerging properties of membrane-bound intrinsically disordered proteins

“…The SH3 domain nucleates an intramolecular fuzzy complex in which the Unique and SH4 domains are loosely tethered around the globular domain, while retaining their disordered character [52]. The intramolecular fuzzy complex is retained in the membrane-bound form bringing the SH3 domain in close proximity to the lipid surface [53]. Thus, globular domains "coated" with disordered proteins can also be an integral part of the DBC (Figure 5).…”

“…However, recent results show that in a LUV-anchored form of c-Src, containing the myristoylated SH4, Unique, and SH3 domains, the additional lipid binding site in the Unique domain is not interacting directly with the liposome. This lipid interacting region, contributes to stabilize the intramolecular interaction of the myristoyl group with the SH3 domain in the non-membrane bound form [53] and modulates the orientation of the globular domains with respect to the membrane surface, via the intramolecular fuzzy complex. The change in orientation may explain the observed change in substrate specificity caused by mutations in the Unique lipid-binding region [Roche, S. private communication, manuscript in preparation], although more complex scenarios cannot be ruled out.…”