NMR structure of F-actin-binding domain of Arg/Abl2 from Homo sapiens.

The Northeast Structural Genomics Consortium has used bioinformatics methods to construct a Human Cancer Pathway Interaction Network (HCPIN),1 a comprehensive 3D structure-function database of human-cancer-associated proteins and protein complexes in the context of their interaction networks. The FABD domain of Arg (Abl-related gene; Abl2) was selected as NESG HCPIN target HR5537. Arg and Abl (Abelson tyrosine kinase; Abl1), the Abl non-receptor tyrosine kinases, link diverse cell surface receptors to the regulation of cytoskeletal dynamics and regulate cytoskeletal reorganization, cell proliferation, survival, adhesion, migration and stress responses in multiple cells types.2–7 Abl and Arg kinases are multi-domain proteins with highly conserved Src kinase homology 3 (SH3), SH2, kinase (SH1) domains in the N-terminal half. The C-terminal halves of these kinases are more divergent, however, the functions encoded by the C-terminus are critical for the overall functions of these proteins.4 Although Abl and Arg exhibit overlapping expression in many tissues, Arg is most highly expressed in brain, thymus, spleen, and muscle.8 Differences in regulation of cell migration by Abl and Arg have also been reported.7 Consistent with the nuclear and cytoplasmic localization of Abl and the predominant cytoplasmic localization of Arg, three nuclear localization signals (NLS), one nuclear export signal NES motifs and a DNA-binding domain are found in Abl but not in Arg.4 Abl and Arg share a C-terminal calponin homology F-actin-binding domain (FABD) with ~44% sequence identity, which distinguishes Abl family kinases from other non-receptor tyrosine kinases.4,9,10 Preceding this shared FABD, Arg has a microtubule-binding (MT) domain and a second talin-like F-actin-binding domain that is characterized by an I/LWEQ sequence while Abl kinase has a globular (G)-actin binding domain.4,9,10,11 Arg uses its FABD to anchoring actin and other cytoskeletal partner for signal transfer and other biological functions.4 Both human Abl FABD and Arg FABD belong to the F_actin_bind protein domain family (Pfam12 entry PF08919) comprised of 21 sequences. The NMR structure of the human Abl FABD, the only available structure in F_actin_bind family, has been reported recently13 ; it forms a compact left-handed four helix bundle in solution. The Arg FABD was selected as HCPIN target by NESG for structure determination.1 The NMR structure of human Arg FABD reported here can serve as a structural basis for elucidating the molecular mechanism of Arg pathway, for studies of protein complex formation, and potentially in small molecule drug design.