The present disclosure relates to a modified polypeptide, in which the activity of meso-diaminopimelate is weakened, and a method for producing L-threonine using the same.

Provided in this disclosure, in some embodiments, are methods and compositions for treating maple syrup urine disease (MSUD) and other conditions characterized by excessive branched-chain amino acids.

Related are a recombinant microorganism for producing L-valine, a construction method and an application thereof. Through transferring an amino acid dehydrogenase gene and/or activating activity of a transhydrogenase and/or a NAD kinase, reducing power of NADPH in cell is increased, the titer and yield of L-valine generated by Escherichia coli are improved, and the production of L-valine by one-step anaerobic fermentation is achieved.

Related are a recombinant microorganism for producing L-valine, a construction method and an application thereof. Through enhancing amino acid dehydrogenase activity of L-valine fermentation strain, and/or activating an Entner-Doudoroff (ED) metabolic pathway, a problem in L-valine fermentation process that reducing power is unbalanced is solved, thereby the titer and yield of L-valine produced by Escherichia coli are improved, and L-valine was produced by one-step anaerobic fermentation.

Provided is an amino acid dehydrogenase mutant. The amino acid sequence of the mutant is obtained by mutating the amino acid sequence shown in SEQ ID NO:1. The mutation includes at least one of the following mutation sites: 64th, 94th, 133rd, 137th, 148th, 168th, 173rd, 183 rd, 191st, 207th, 229th, 248th, 255th and 282nd sites; or the amino acid sequence of the amino acid dehydrogenase mutant is an amino acid sequence having the mutation sites in the mutated amino acid sequence and having a 80% or more homology with the mutated amino acid sequence. The mutant enzyme activity is more than 50 times higher than that of wild amino acid dehydrogenase, and the enzyme specificity is also correspondingly improved.

Related are a recombinant microorganism for producing L-valine, a construction method and an application thereof. Through transferring an acetohydroxy acid reductoisomerase gene and/or an amino acid dehydrogenase gene into a microorganism, and enhancing activity of an acetohydroxy acid reductoisomerase and/or an amino acid dehydrogenase, the titer and yield of L-valine generated by Escherichia coli may be improved, and L-valine was produced by one-step anaerobic fermentation.

Provided are an L-glutamate dehydrogenase mutant and an application thereof, the mutant mutating the amino acid residue A at position 166 and/or the amino acid residue V at position 376 shown in SEQ ID NO. 1 into a hydrophilic or small sterically hindered amino acid residue, the application performing an amination reaction of 2-oxo-4-(hydroxymethylphosphinyl)butyrate in the presence of an L-amino acid dehydrogenase mutant, an inorganic amino donor, and a reduced coenzyme NADPH, and performing an acidification reaction on the obtained L-glufosinate salt to obtain L-glufosinate. Compared to wild L-glutamate dehydrogenase, the present L-glutamate dehydrogenase mutant has a higher concentration of substrates that can be catalysed when preparing L-glufosinate, thereby increasing the efficiency of the action of the enzyme and reducing reaction costs.

The present invention discloses a method for preparing L-glufosinate ammonium by biological enzymatic de-racemization, a glufosinate ammonium dehydrogenase mutant and a use thereof. The method for preparing L-glufosinate ammonium by biological enzymatic de-racemization includes catalyzing D,L-glufosinate ammonium as a raw material by a multi-enzyme catalysis system to obtain L-glufosinate ammonium. The enzyme catalysis system includes D-amino acid oxidase for catalyzing D-glufosinate ammonium in the D,L-glufosinate ammonium to 2-carbonyl-4-[hydroxy(methyl)phosphonyl]butanoic acid, and a glufosinate ammonium dehydrogenase mutant for catalytically reducing 2-carbonyl-4-[hydroxy(methyl)phosphonyl]butanoic acid to L-glufosinate ammonium. The glufosinate ammonium dehydrogenase mutant is obtained by mutation of glufosinate-ammonium dehydrogenase in wild fungi Thiopseudomonas denitrificans at a mutation site of V377S. The glufosinate ammonium dehydrogenase mutant in the present invention has better catalytic efficiency. When racemic D, L-glufosinate ammonium is used as a substrate for a catalytic reaction, the conversion rate is much higher than the conversion rate of a wild-type enzyme, and the yield of 2-carbonyl-4-[hydroxy(methyl)phosphonyl]butanoic acid (PPO for short) is also greatly improved.

A genetically engineered strain having high-yield of L-valine is disclosed. Starting from Escherichia coli W3110, an acetolactate synthase gene alsS of Bacillus subtilis is inserted into a genome thereof and overexpressed; a ppGpp 3′-pyrophosphate hydrolase mutant R290E/K292D gene spoTM of Escherichia coli is inserted into the genome and overexpressed; a lactate dehydrogenase gene ldhA, a pyruvate formate lyase I gene pflB, and genes frdA, frdB, frdC, frdD of four subunits of fumaric acid reductase are deleted from the genome; a leucine dehydrogenase gene bcd of Bacillus subtilis replaces a branched chain amino acid transaminase gene ilvE of Escherichia coli; and an acetohydroxy acid isomeroreductase mutant L67E/R68F/K75E gene ilvCM replaces the native acetohydroxy acid isomeroreductase gene ilvC of Escherichia coli. Furthermore, the L-valine fermentation method is improved by using a two-stage dissolved oxygen control. The L-valine titer and the sugar-acid conversion rate are increased.

Described herein are an immobilized enzyme, and a preparation method therefor and a use thereof. The immobilized enzyme includes activated PEI and an enzyme covalently bonded to the activated PEI, where the enzyme is selected from any one of a transaminase, a ketoreductase, a monooxygenase, an ammonia lyase, an ene-reductase, an imine reductase, an amino acid dehydrogenase and a nitrilase.