Probing the Recognition Properties of the Antiparallel Coiled Coil Motif from PKN by Protein Grafting

Coiled coils have long been recognized as the major constituent of many fibrous proteins and also serve as oligomerization domains in a wide variety of proteins. More recently, it has become clear that the surfaces of two-stranded coiled coils are also involved in macromolecular recognition. Indeed, the helical hairpin or intramolecular antiparallel coiled coil (ACC) can serve as a protein or nucleic acid recognition motif. Protein kinase N (PKN) interacts with the small GTPase RhoA through ACC motifs. The crystal structure of RhoA with the N-terminal ACC motif (PKN-ACC1) is unusual in that these proteins interact through two distinct surfaces. Using the ACC domain of seryl tRNA synthetase (SRS-ACC) as a scaffold for protein grafting experiments, we show that RhoA interacts with only one face of PKN-ACC1. This result highlights the potential of the SRS-ACC scaffold for protein engineering applications and provides insight into the mechanism of RhoA-mediated signal transduction through PKN.