COMMD6 from amphioxus Branchiostoma belcheri (BbCOMMD6) interacts with creatine kinase and inhibits its activity

COMM domain-containing proteins are a group of recently discovered proteins; their biochemical characterization remains much limited. Here we demonstrate that a cDNA encoding Branchiostoma belcheri COMMD6, designated BbCOMMD6, codes for a protein of 203 amino acids, with a COMM domain at its C-terminal region and an extended N-terminal portion. BbCOMMD6 is mainly present in the cytosol. In contrast to COMMD1, the presence of Cu(II) cannot enhance recombinant BbCOMMD6 dimer formation. Both the pull-down and reverse pull-down assays reveal that BbCOMMD6 interacts with the creatine kinase (CK), an essential enzyme involved in energy metabolism, forming a heterodimer BbCOMMD6-CK. The enzymatic activity assays show that CK activities are inhibited by BbCOMMD6 in a dose-dependent manner. All these data suggest that BbCOMMD6 is involved in energy transduction, via binding to CK and inhibiting activities of CK, and offer first clues to its role as a regulator of CK activities.