Abstract
Hyaluronic acid (HA) is widely used in food and pharmaceutical industries. As a UDP-glucose dehydrogenase, hasB catalyzes the conversion of UDP-Glc to UDP-GlcUA in HA biosynthesis. However, little is known about structural characteristic and enzymatic property of hasB. Owing to high-yield HA production by Streptococcus zooepidemicus CR003, an in-depth analysis of hasB from CR003 was investigated in this work. HasB contains 401 amino acids with a molecular weight of 44.96 kDa, which exhibited 62.69 % homology with that from S. pyogenes. The optimal reaction condition for the purified hasB by heterologous expression was 30 °C and pH 9.0. Cu2+ and Zn2+ significantly inhibited hasB activity, whereas Mg2+ had a stimulatory effect. Km values of hasB for UDP-Glc and NAD+ were 0.1378 and 0.7583 mM, and Vmax were 391.3 and 548.8 μmol/min/mg, respectively. To our knowledge, it is currently the highest reported enzyme catalytic activity of hasB. Molecular docking showed that the binding energies of hasB with UDP-Glc and NAD+ were −731.01 and −314.17 kcal/mol, respectively, and the interaction forces between hasB and the substrate play a crucial role in stabilizing the conformation of protein-substrate complexes. Conclusively, hasB from CR003 showed high catalytic efficiency, which has great application potential for HA production.
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