Cloning and Expression of the Mutanase Gene of Paenibacillus humicus from Fermented Food

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There has been much interest in mutanases, α-1,3-glucanases, as they have the potential for preventive agents in the oral cavity. Mutanases have been reported in some bacteria and fungi but remain a relatively uncharacterized family of enzymes. We screened bacterial mutanase in fermented food for the application of the enzyme to preventive medicine. Immersed solutions of fermented soybeans, natto, on mutan-containing agar plates exhibited mutan-hydrolyzing activity after incubation. We isolated a microorganism that hydrolyzed mutan from the fermented soybeans and named it Paenibacillus humicus strain NA1123. The gene for the mutanase was cloned, and the nucleotide sequence of the gene consisted of 3441-bp open reading frame that encoded a predicted 1146-amino acid polypeptide including a 33-amino acid signaling peptide. The predicted molecular mass of the matured enzyme was 115399. The protein is composed of an N-terminal domain and a C-terminal domain, that are connected by a sequence composed of proline and threonine repeats. The deduced amino acid sequence of the present enzyme showed similarity to that of the mutanase MuC1 of strain KSM-M126 and the mutanase MuE of strain KSM-M318 of Paenibacillus sp. with 77.2% and 73.5% identity, respectively. We confirmed that the recombinant mutanase exhibited mutan hydrolyzing activity.