Yonekawa Tohru, Ohnishi Yasuo, Horinouchi Sueharu
Department of Biotechnology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
FEMS Microbiol Lett. 2005 Mar 15;244(2):315-21. doi: 10.1016/j.femsle.2005.02.003.
The gene, named cabB, encoding a calmodulin-like protein of 70 amino acids containing two helix-loop-helix EF-hand motifs was cloned from Streptomyces coelicolor A3(2). cabB was transcribed from a single promoter throughout growth. The CabB protein produced in Escherichia coli was a monomer in solution, although it corresponded to one half of a dumbbell shape of the eukaryotic calmodulins. CabB bound calcium and upon binding of calcium its alpha-helix content was increased, as determined by circular dichroism spectroscopy. The growth of cabB-disruptants (mutant DeltacabB) on minimal agar medium containing calcium higher than 20 mM was delayed, suggesting that CabB has a role in calcium homeostasis by serving as a calcium buffer or transporter, as suggested for calerythrin in actinomycetes and the invertebrate sarcoplasmic calcium-binding proteins. Wide distribution of cabB almost exclusively in actinomycetes suggests a common role of EF-hand CabB-type proteins in these filamentous, soil-dwelling Gram-positive bacterial genera.
