Biochemical and Structural Studies of the Interaction between ARAP1 and CIN85.

Arf-GAP with Rho-GAP domain, ANK repeat and PH domain-containing protein 1 (ARAP1), Cbl-interacting protein of 85 kDa (CIN85), and casitas B-lineage lymphoma (Cbl) play important roles in epidermal growth factor receptor (EGFR) internalization and recycling. In previous studies, ARAP1 was found to interact with CIN85, and their interaction attenuated the ubiquitination of EGFR. However, the molecular mechanism was still unclear. In this study, we first biochemically and structurally characterized the interaction between ARAP1 and CIN85, and found that the CIN85 SH3B domain bound to the ARAP1 PXPXXRX (except P) XXR/H/K motif with high affinity and specificity. Based on this binding model, we further predicted other potential CIN85 binding partners and tested their interactions biochemically. Moreover, our swapping data and structure alignment analysis suggested that the β2-β3 loops of the CIN85 SH3 domains and the H87/E132 interaction were critical for ARAP1 binding specificity. Finally, our competitive analytical gel-filtration chromatography and isothermal titration calorimetry (ITC) results showed that ARAP1 could compete with Cbl for CIN85 binding, which provides a biochemical basis for the regulatory roles of ARAP1 in the CIN85-mediated EGFR internalizing process.