Structure, Dynamics, and Function of the Membrane Associated SRC Family Kinase HCK

Abstract

The Src family kinases (SFKs) are a group of nine non-receptor tyrosine kinases known for their involvement in critical signal transduction pathways. Structurally, SFKs share a common multi-domain architecture, consisting of SH3, SH2, and catalytic (SH1) domains attached to a membrane-anchoring SH4 domain through an intrinsically disordered ∼80 residue region of low sequence conservation called the Unique (U) domain. Despite the wealth of information on SFK structure and function, little is known about the nature of these enzymes in the membrane-associated form. Interestingly, SH4-U domains in different species share common sequence features, despite differences between SFK members, arguing for their importance in differentiating the functions of SFKs and raising questions about their ability to participate in SFK signaling.Hematopoetic cell kinase (Hck), a phagocyte specific proto-oncogene member of the SFKs, is a potential drug target for HIV infections and Bcr/Abl-chronic myeloid leukemia. To achieve structural characterization of the membrane-associated Hck via its SH4-U domains, data from solution and solid-state NMR, neutron reflection, and fluorescence resonance energy transfer were computationally integrated using a novel maximum-entropy multi-resolution “restrained-ensemble molecular dynamics” (reMD) simulation scheme. This framework has allowed us to detail features of the membrane-protein complex at atomic resolution and identify possible new constraints on Hck's ability to phosphorylate downstream targets. In vivo assays are being developed to test the relevance of these findings.