Creatine kinase is a bacteriostatic factor with a lectin-like activity

Creatine kinase (CK), an enzyme catalyzing the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP), has been shown to be an acute phase reactant in the amphioxus Branchiostoma belcheri. However, immune and functional characterization of this protein remains lacking. Here we demonstrate clearly that the expression of B. belcheri gene, BbCK, was inducible by the challenge with LPS, and the recombinant BbCK was capable of binding to the Gram-negative bacterium Escherichia coli and inhibiting the bacterial growth. Moreover, the bacteriostatic activity of the recombinant BbCK against E. coli was able to be suppressed by some sugars including N-acetyl-d-mannosamine, N-acetyl-d-glucosamine, l-fucose, d-mannose, d-fructose and d-glucose. In contrast, BbCK exerted little effect on the growth of the Gram-positive bactterium Staphylococcus aureus. Taken together, these data suggest that CK is a bacteriostatic factor with a lectin-like activity, capable of specifically inhibiting the growth of the Gram-negative bacteria like E. coli. This is the first report exhibiting the integrative role of CK in immunity via its pleiotropic effects on recognizing the Gram-negative bacterium E. coli and inhibiting its growth.