AUTHOR=Liu Xinyang , Liu Jiao , Liu Zhemin , Qiao Qianqian , Ni Xiaomeng , Yang Jinxing , Sun Guannan , Li Fanghe , Zhou Wenjuan , Guo Xuan , Chen Jiuzhou , Jia Shiru , Zheng Yu , Zheng Ping , Sun Jibin TITLE=Engineering allosteric inhibition of homoserine dehydrogenase by semi-rational saturation mutagenesis screening JOURNAL=Frontiers in Bioengineering and Biotechnology VOLUME=11 YEAR=2024 URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2023.1336215 DOI=10.3389/fbioe.2023.1336215 ISSN=2296-4185 ABSTRACT=

Allosteric regulation by pathway products plays a vital role in amino acid metabolism. Homoserine dehydrogenase (HSD), the key enzyme for the biosynthesis of various aspartate family amino acids, is subject to feedback inhibition by l-threonine and l-isoleucine. The desensitized mutants with the potential for amino acid production remain limited. Herein, a semi-rational approach was proposed to relieve the feedback inhibition. HSD from Corynebacterium glutamicum (CgHSD) was first characterized as a homotetramer, and nine conservative sites at the tetramer interface were selected for saturation mutagenesis by structural simulations and sequence analysis. Then, we established a high-throughput screening (HTS) method based on resistance to l-threonine analog and successfully acquired two dominant mutants (I397V and A384D). Compared with the best-ever reported desensitized mutant G378E, both new mutants qualified the engineered strains with higher production of CgHSD-dependent amino acids. The mutant and wild-type enzymes were purified and assessed in the presence or absence of inhibitors. Both purified mutants maintained >90% activity with 10 mM l-threonine or 25 mM l-isoleucine. Moreover, they showed >50% higher specific activities than G378E without inhibitors. This work provides two competitive alternatives for constructing cell factories of CgHSD-related amino acids and derivatives. Moreover, the proposed approach can be applied to engineering other allosteric enzymes in the amino acid synthesis pathway.