A novel adapter protein employs a phosphotyrosine binding domain and exceptionally basic N-terminal domains to capture and localize an atypical protein kinase C: characterization of Caenorhabditis elegans C kinase adapter 1, a protein that avidly binds protein kinase C3.

Atypical protein kinase C isoforms transmit regulatory signals to effector proteins located in the cytoplasm, nucleus, cytoskeleton, and membranes. Mechanisms by which encounter and control effector proteins in various microenvironments are poorly understood. By using a protein interaction screen, we discovered two novel proteins that adapt a Caenorhabditis elegans for specialized (localized) functions; protein kinase C adapter 1 (CKA1, 593 amino acids) and CKA1S (549 amino acids) are derived from a unique mRNA by alternative utilization of two translation initiation codons. CKA1S and CKA1 are routed to the cell periphery by exceptionally basic N-terminal regions that include classical phosphorylation site domains (PSDs). Tethering of is mediated by a segment of CKA1 that constitutes a phosphotyrosine binding (PTB) domain. Two aromatic amino acids (Phe(175) and Phe(221)) are indispensable for creation of a surface and/or stabilization of complexes. Patterns of CKA1 gene promoter activity and CKA1/CKA1S protein localization in vivo overlap with patterns established for duanyu15313 expression and distribution. Transfection experiments demonstrated that CKA1/CKA1S sequesters duanyu15313 in intact cells. Structural information in CKA1/CKA1S enables delivery of adapters to the lateral plasma membrane surface (near tight junctions) in polarized epithelial cells. Thus, a PTB domain and PSDs collaborate in a novel fashion in CKA1/CKA1S to enable tethering and targeting of Avid ligation of a isoform is a previously unappreciated function for a PTB module.

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