Abstract 2919: The structural basis of BCR-ABL recruitment of GRB2 in chronic myelogenous leukemia
Authors: Liu Yonglan , Jang Hyunbum , Zhang Mingzhen , Tsai Chung-Jung , Maloney Ryan , Nussinov Ruth 
Published: June 2022

Abstract
Philadelphia chromosomes 9 and 22 encode BCR and ABL1 genes, respectively. Translocation mutation of two chromosomes generates the fused BCR-ABL1 gene. The resulting fused gene encodes the chimeric BCR-ABL oncoprotein with constitutively enhanced and dysregulated tyrosine activity to disturb different cell signaling. Ras/MAPK is a significant pathway in mediating cell proliferation and its hyperactivation is responsible for malignant transformation in cancer. Autophosphorylation Y177 (pY177) of BCR protein stimulates the direct binding of an adaptor protein GRB2, which is involved in Ras/MAPK pathway. In BCR-ABL-associated Ras/MAPK signaling pathway, BCR-ABL can target GRB2 through the interaction of its pY motif with GRB2 SH2 domain, followed by SOS recruitment to the plasma membrane by GRB2. The resulting BCR-ABL/GRB2/SOS assembly stimulates the transformation of inactive GDP-bound form of Ras to the active GTP-bound state, which causes the constitutive activation of the downstream components of Raf/MEK/ERK. Despite a number of biophysical experiments have showed that BCR-ABL is able to recruit GRB2, the molecular-level understanding of how the two proteins interact with each other remains to be elucidated. In this work, we used molecular modeling and molecular dynamics (MD) simulations to study the structural basis for the binding between BCR-ABL and GRB2 SH2 domain to explain CML oncogenesis at the atomic level. Different pY/Y-peptide-SH2 complex models have been constructed and their binding specificity and affinity were compared. Simulation results showed that phosphorylated BCR (pBCR) specifically binds to GRB2 SH2 domain through its five-residue 176FpYVNV180 motif. GRB2 SH2 domain contains two binding pockets: the pY-binding pocket for the phosphate recognition and the specificity pocket for the selection of Asn. pY177 triggers the binding through the interaction in pY-binding pocket. The interaction in specificity pocket determines the binding specificity, which is regulated by N179 in pBCR and W121 in EF loop of GRB2 SH2 domain. In addition, the interaction in the specificity pocket experiences conformation selection for both the bound motif in pBCR and GRB2 SH2 domain; the binding motif adopts type I β-turn conformation and the specificity pocket of GRB2 SH2 domain displays the closed conformation. This specific binding mode between pBCR and GRB2 SH2 domain is similar with that between phosphorylated EGFR (pEGFR) and GRB2 SH2 domain. Residues adjacent to the pY and Arg residue at the +2 position C-terminal to pY in the binding motifs influence the binding affinity of a pY-peptide to GRB2 SH2 domain, explaining why pBCR shows stronger affinity to GRB2 SH2 domain than pEGFR. Our study supports the BCR-ABL oncoprotein recruitment of GRB2 for the induction of CML through Ras/MAPK pathway and provides deeply understanding of the specific interaction of the pY motif with GRB2 SH2 domain at atomic level.
Citation Format: Yonglan Liu, Hyunbum Jang, Mingzhen Zhang, Chung-Jung Tsai, Ryan Maloney, Ruth Nussinov. The structural basis of BCR-ABL recruitment of GRB2 in chronic myelogenous leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2919.