GAKIN, a novel kinesin-like protein associates with the human homologue ofthe Drosophila discs large tumor suppressor in T lymphocytes

Reorganization of the cortical cytoskeleton is a hallmark of T lymphocyte a ctivation, Upon binding to antigen presenting cells, the T cells rapidly un dergo cytoskeletal re-organization thus forming a cap at the cell-cell cont act site leading to receptor clustering, protein segregation, and cellular polarization. Previously, we reported cloning of the human lymphocyte homol ogue of the Drosophila Discs Large tumor suppressor protein (hDlg), Here we show that a novel protein termed GAKIN binds to the guanylate kinase-like domain of hDlg, Affinity protein purification, peptide sequencing, and clon ing of GAKIN cDNA from Jurkat J77 lymphocytes identified GAKIN as a novel m ember of the kinesin superfamily of motor proteins. GAKIN mRNA is ubiquitou sly expressed, and the predicted amino acid sequence shares significant seq uence similarity with the Drosophila kinesin-73 motor protein. GAKIN sequen ce contains a motor domain at the NH, terminus, a central stalk domain, and a putative microtubule-interacting sequence called the CAP-Gly domain at t he COOH terminus, Among the MAGUK superfamily of proteins examined, GAKIN b inds to the guanylate kinase-like domain of PSD-95 but not of p55. The hDlg and GAKIN are localized mainly in the cytoplasm of resting T lymphocytes, however, upon CD2 receptor cross-linking the hDlg can translocate to the ly mphocyte cap. We propose that the GAKIN-hDlg interaction lays the foundatio n for a general paradigm of coupling MAGUKs to the microtubule-based cytosk eleton, and that this interaction may be functionally important for the int racellular trafficking of MAGUKs and associated protein complexes in vivo.