Mutagenetic study of a novel inosine monophosphate dehydrogenase from Bacillus amyloliquefaciens and its possible application in guanosine production

In this study, the amino acid sequence of inosine monophosphate dehydrogenase (IMPDH) from a guanosine-overproducing strain Bacillus amyloliquefaciens TA208 was found to be highly conserved comparing to its analogue in B. amyloliquefaciens FZB42, only with two substitutions of serine 166 to proline and glutamic acid 481 to lysine. To speculate on the effects of these variation sites, two reverse site-directed mutants P166S and K481E, as well as one deletion mutant IMPDHΔCBS, were characterised. According to the kinetic analysis of these enzymes, site-481 is a key mutation site to affect the nicotinamide adenine dinucleotide (NAD+) affinity, which accounted for the higher catalytic efficiency of IMPDH. On the contrary, mutants P166S and IMPDHΔCBS did not show better catalytic activity compared to normal IMPDH. Moreover, the overexpression of IMPDH-encoding gene guaB in B. amyloliquefaciens TA208 could improve the total production of guanosine up to 13.5 g L-1, which was 20.02% higher than that of the original strain.