One of protein kinase C (PKC) isozymes, PKC beta binds to receptor for activated C kinase 1 (RACK1), and their complex is suggested to be translocated to melanosomes. The binding site of PKC beta for RACK1 is considered one of its catalytic domains, V5 domain which consists of three motifs such as V5-1, V5-2, and V5-3. Among these, V5-I region, extreme C-terminal residues of PKC beta showed the highest RACK1-binding affinity. PKC beta can be classified into PKC beta I and PKC beta II based on their different V5 domains. RACK1-binding affinity of PKC beta II is five times greater than that of PKC beta I. The structures of PKC beta I, PKC beta II, and RACK1 are not known. However, the conformational study on PKC beta II V5-1 region showing high RACK1-binding selectivity may help us in understanding the interaction between RACK1 and PKC beta II. (c) 2005 Elsevier Inc. All rights reserved.