The present research work explores the Nattokinase (NK) producing capacity of five Bacillus subtilis strains (MTCC 2616, MTCC 2756, MTCC 2451, MTCC 1427, and MTCC 7164) using soybean varieties as substrate under solid-state fermentation conditions. Subsequently, the biochemical attributes of NKs were analyzed. Soybean variety didn't affect the production of NK to a significant extent; however, the five strains differed substantially for their NK producing capacity. NK produced by MTCC 2451 (R3) showed a low Kmvalue implying its higher specificity for fibrin but this strain (MTCC 2451) didn't produce NK in sufficient quantity. The low Km of MTCC 2451 NK implicates its potential candidature for treating blood clots in cardiovascular patients. The NK produced by MTCC 2616 (R1) was produced in sufficient quantity and showed good fibrin dissolving potential. The aprN of MTCC 2616 substantially varied from the other four strains. The aprN of MTCC 2756 (R2), MTCC 2451 (R3), MTCC 1427 (R4), and MTCC 7164 (R5) shared > 99% sequence identity, but the encoded NKs had significant variations in their Km values. The biochemical-molecular analyses indicate the co-presence of three critical residues (Thr130, Asp140, and Tyr217) as a quintessential attribute in determining the low Km of NK enzymes, and the absence of any one of the three critical residues may affect (highly increase) the Km.
Keywords: B. subtilis; Fermentation; Homology modeling; Nattokinase; aprN gene.
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