Enhanced protein glutaminase production from Chryseobacterium proteolyticum combining physico‐chemical mutagenesis and resistance screening and its application to soybean protein isolates

Abstract

BACKGROUND Protein glutaminase (PG) is a novel protein modification biotechnology that is increasingly being used in the food industry. However, the current level of fermentation of PG‐producing strains still does not meet the requirements of industrial production. To obtain the mutant strains with high PG production, the atmospheric and room temperature plasma (ARTP) combined with LiCl chemical mutagen were used in mutagenesis of a PG producing Chryseobacterium proteolyticum 1003. RESULTS A mutant strain (WG15) was successfully obtained based on malonic acid resistance screening after compound mutagenesis of the starting strain C. proteolyticum 1003 using ARTP with LiCl, and it was confirmed to be genetically stable in PG synthesis after 15 generations. The protein glutaminase production of WG15 was 2.91 U mL−1 after optimization of fermentation conditions, which is 48.69% higher than the original strain C. proteolyticum 1003. The PG obtained from fermentation showed good activities in deamidation of soy protein isolate. The solubility and foaming properties of the PG‐treated soy protein isolate were significantly increased by 36.50% and 10.03%, respectively, when PG was added at the amount of 100 U mL−1. In addition, the emulsifying activity and emulsion stability of the treated soy protein isolate were improved by 12.44% and 10.34%, respectively, on the addition of 10 U mL−1 PG. The secondary structure of the soy protein isolate changed after PG treatment, with an increased proportion of glutamate. CONCLUSION The results of the present study indicate that the PG produced by this mutant strain could improve the functional properties of soybean protein isolate and the C. proteolyticum mutant WG15 has great potential in food industry. © 2023 Society of Chemical Industry.

Recombinant Protein Glutaminase from Probiotic Escherichia coli Nissle 1917 for Enhancing the Functional Properties of Caseins

“…The natural PG-producing strain was discovered in C. proteolyticum 9670 T , isolated from the soil in 2000 (Yamaguchi & Yokoe, 2000), which was proven to be food safe (Scheuplein, et al, 2007) and certi ed as a generally recognized as safe (GRAS) strain by US FDA. However, as of present, the recently reported yield of PG in C. proteolyticum is only 2.91 U/mL, which is far below the requirement for industrial applications in the food processing industry (Wang, et al, 2023). Heterologous expression is an alternative strategy to overcome this problem.…”

“…Currently, The maximum PG enzyme activity of 0.175 U/mL was achieved in E. coli (Lu, et al, 2020). The PG enzyme activity of 7.07 U/mL and 26 U/mg were achieved in Bacillus subtilis (Ouyang, et al, 2021;Yin, et al, 2021) and Corynebacterium glutamicum (Kikuchi, et al, 2008;Qu, et al, 2022;Wang, et al, 2023), respectively. Unfortunately, the expression effect of E. coli, which is the preferred host for superior heterologous gene expression, seems to be not optimistic for PG production.…”