Azasugar biosynthesis involves a key dehydrogenase that oxidizes 2-amino-2-deoxy-D-mannitol to the 6-oxo
compound. The genes encoding homologous NAD-dependent dehydrogenases from Bacillus amyloliquefaciens FZB42, B.
atrophaeus 1942, and Paenibacillus polymyxa SC2 were codon-optimized and expressed in BL21(DE3) Escherichia coli.
Relative to the two Bacillus enzymes, the enzyme from P. polymyxa proved to have superior catalytic properties with a
Vmax of 0.095 ± 0.002 µmol/min/mg, 59-fold higher than the B. amyloliquefaciens enzyme. The preferred substrate is 2-
amino-2-deoxy-D-mannitol, though mannitol is accepted as a poor substrate at 3% of the relative rate. Simple amino alcohols
were also accepted as substrates at lower rates. Sequence alignment suggested D283 was involved in the enzyme’s
specificity for aminopolyols. Point mutant D283N lost its amino specificity, accepting mannitol at 45% the rate observed
for 2-amino-2-deoxy-D-mannitol. These results provide the first characterization of this class of zinc-dependent medium
chain dehydrogenases that utilize aminopolyol substrates.
Azasugar
生物合成涉及一种关键的脱氢酶,该酶将2-
氨基-2-脱氧-
D-甘露糖氧化为6-氧代化合物。编码来自淀粉芽孢杆菌FZB42、萎缩芽孢杆菌1942和多粘类芽孢杆菌SC2的同源
NAD依赖性脱氢酶的
基因经过密码子优化,并在B
L21(DE3)大肠杆菌中表达。与两种芽孢杆菌的酶相比,多粘类芽孢杆菌的酶具有更优越的催化性能,Vmax为0.095±0.002微摩尔/分钟/毫克,比淀粉芽孢杆菌的酶高59倍。首选底物是2-
氨基-2-脱氧-
D-甘露糖,但
甘露糖被认为是一种较差的底物,相对速率仅为3%。简单的
氨基醇也被认为是底物,但速率较低。序列比对表明,D283参与了酶对
氨基多元醇的专一性。点突变体D283N失去了
氨基专一性,
甘露糖的接受速率是2-
氨基-2-脱氧-
D-甘露糖的45%。这些结果首次描述了这类利用
氨基多元醇底物的
锌依赖性中链脱氢酶的特征。