JLP associates with kinesin light chain 1 through a novel leucine zipper-like domain.

Scaffolding proteins exist in eukaryotes to properly assemble signaling proteins into specific multimeric functional complexes. JLP is a novel leucine zipper protein belonging to a family of scaffolding proteins that assemble JNK signaling modules. JLP is a proline-rich protein that contains two leucine zipper domains and a highly conserved C-terminal domain. We have identified kinesin light chain 1 (KLC1) as a binding partner for the second leucine zipper domain of JLP using yeast two-hybrid screening. The interaction domain of KLC1 was mapped to its tetratripeptide repeat, which contains a novel leucine zipper-like domain that is crucial for the interaction with JLP. Mutations of Leu-280, Leu-287, Val-294, and Leu-301 within this domain of KLC1 disrupted its ability to associate with JLP. Immunofluorescence studies showed that JLP and KLC1 co-localized in the cytoplasm and that the localization of JLP was dependent on its second leucine zipper. Ectopic expression of a dominant negative form of KLC1 resulted in the mislocalization of endogenous JLP. Moreover, the association between JLP and KLC1 occurred in vivo and was important in the formation of ternary complex with JNK1. These results identify a novel protein-protein interaction between KLC1 and JLP that involves leucine zipper-like domains and support the role of motor proteins in the spatial regulation of signaling modules.