The ycaC-related protein from the amphioxus Branchiostoma belcheri (BbycaCR) interacts with creatine kinase.

The ycaC-related gene, ycaCR, is uncharacterized, and has no assigned function to date. Here we clearly showed that the ycaC-related gene from the amphioxus Branchiostoma belcheri, BbycaCR, coded for a novel member of the isochorismatase superfamily, which is mainly localized in the mitochondrial fraction. Both pull-down and reverse pull-down analyses revealed that BbycaCR was able to interact with creatine kinase, an enzyme involved in energy transduction, in addition to binding to native ycaCR, forming a homopolymer. Surprisingly, neither isochorismatase, nicotinamidase nor N-carbamoylsarcosine amidohydrolase activity was detected for BbycaCR, although it possessed the putative catalytic triad of Asp19, Arg(Lys)84 and Cys118 that is found in ycaC proteins. Both tissue section in situ hybridization and immunohistochemistry showed that BbycaCR was ubiquitously expressed in amphioxus, although at different expression levels, suggesting that BbycaCR plays a conserved fundamental cellular role in amphioxus. It is proposed that BbycaCR may be indirectly involved in energy transduction.

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