Solution structure of the AF-6 PDZ domain complexed with the C-terminal peptide from the Bcr protein
[AFAD_HUMAN] Note=A chromosomal aberration involving MLLT4 is associated with acute leukemias. Translocation t(6;11)(q27;q23) with MLL/HRX. The result is a rogue activator protein. [BCR_HUMAN] Note=A chromosomal aberration involving BCR is a cause of chronic myeloid leukemia. Translocation t(9;22)(q34;q11) with ABL1. The translocation produces a BCR-ABL found also in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL).
[AFAD_HUMAN] Belongs to an adhesion system, probably together with the E-cadherin-catenin system, which plays a role in the organization of homotypic, interneuronal and heterotypic cell-cell adherens junctions (AJs). Nectin- and actin-filament-binding protein that connects nectin to the actin cytoskeleton. [BCR_HUMAN] GTPase-activating protein for RAC1 and CDC42. Promotes the exchange of RAC or CDC42-bound GDP by GTP, thereby activating them. Displays serine/threonine kinase activity. 
Publication Abstract from PubMed
The human AF-6, a scaffold protein between cell membrane-associated proteins and the actin cytoskeleton, plays an important role in special cell-cell junctions and signal transduction. It can be phosphorylated by the protein kinase Bcr, which allows efficient binding of the C terminus of Bcr to the PDZ domain of AF-6 and consequently enhances the binding affinity of AF-6 to Ras. Formation of the AF-6, Bcr, and Ras ternary complex results in down-regulation of the Ras-mediated signal transduction pathway. To better understand the molecular basis for the recognition of the AF-6 PDZ domain and Bcr, we solve the solution structure of the AF-6 PDZ domain complexed with the C-terminal peptide of Bcr and explore the interactions between them in detail. Compared with previously reported structures, the complex exhibits a noncanonical binding mode of PDZ/peptide. Owing to the distinct residues involved in the AF-6 PDZ domain and Bcr peptide interaction, the interaction mode does not adapt to the existing classification rules that have been put forward, based on the ligand or the PDZ domain specificity. Furthermore, the PDZ domain of AF-6 can bind to the C terminus of Bcr efficiently after phosphorylation of AF-6 by the Bcr kinase. The phosphorylation may induce a conformational change of AF-6, which makes the binding surface on the PDZ domain accessible to Bcr for efficient binding. This study not only characterizes the structural details of the AF-6 PDZ/Bcr peptide complex, but also provides a potential target for future drug design and disease therapy.
Solution structure and backbone dynamics of the AF-6 PDZ domain/Bcr peptide complex.,Chen Q, Niu X, Xu Y, Wu J, Shi Y Protein Sci. 2007 Jun;16(6):1053-62. Epub 2007 May 1. PMID:17473018
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.