p80 ROKalpha binding protein is a novel splice variant of CRMP-1 which associates with CRMP-2 and modulates RhoA-induced neuronal morphology.

Using antibody against the Rho binding domain of ROKalpha, two neuronal phosphoproteins of 62 and 80 kDa were co-immunoprecipitated from brain extracts. Peptide analysis revealed their identity as collapsin response mediator proteins (CRMPs); p62 was CRMP-2 whereas p80 was a novel splice form of CRMP-1 with an extended N-terminus. p80 CRMP-1 was able to complex with CRMP-2, suggesting that p80 CRMP-1 and CRMP-2 form oligomers. CRMP-2 was the major substrate of ROK. p80 CRMP-1 interacted with the kinase domain of ROKalpha, resulting in inhibition of the catalytic activity towards other substrates. Over-expression of p80 CRMP-1 and CRMP-2 together counteracted the effects of RhoA on neurite retraction, an effect enhanced by mutation of the ROK phosphorylation site in CRMP-2. p80 CRMP-1 and CRMP-2 may be modulators of RhoA-dependent signaling, through interaction with and regulation of ROKalpha.