Solution structure and p43 binding of the p38 leucine zipper motif: coiled-coil interactions mediate the association between p38 and p43.

p38, which has been suggested to be a scaffold protein for the assembly of a macromolecular tRNA synthetase complex, contains a leucine zipper-like motif. To understand the importance of the leucine zipper-like motif of p38 (p38LZ) in macromolecular assembly, the p38LZ solution structure was investigated by circular dichroism and nuclear magnetic resonance spectroscopy. The solution structure of p38LZ showed an amphipathic alpha-helical structure and characteristics similar to a coiled-coil motif. The protein-protein interaction mediated by p38LZ was examined by an in vitro binding assay. The p43 protein, another non-synthetase component of the complex, could bind to p38LZ via its N-terminal domain, which is also predicted to have a potential coiled-coil motif. Thus, we propose that the p38-p43 complex would be formed by coiled-coil interactions, and the formation of the binary complex would facilitate the macromolecular assembly of aminoacyl-tRNA synthetases.