Understanding and Engineering Glycine Cleavage System and Related Metabolic Pathways for C1-Based Biosynthesis

The glycine cleavage system (GCS) is a fundamental component of life, widely existing in microbes, plants, animals, and humans. A better understanding of the functionality and working mechanisms, and the engineering of the GCS have both scientific and practical impacts, which may lead to new knowledge and findings in life sciences, improved biomass production and human/animal health, efficient biosynthesis of chemicals, effective carbon fixation and global climate change mitigation. In this chapter, the GCS is first discussed in the context of the reductive glycine pathway (rGlyP), a recently proposed and appealing assimilation pathway of CO₂ and formate, and its implementation and optimization in microorganisms for formatotrophic growth. Then, the present knowledge about the components, reactions, and working mechanisms of the GCS and related enzymes is reviewed. Particular emphasis is also placed on the conformational and structural features of the GCS proteins, especially the different forms of lipoylated H protein and its lipoylation by lipoate protein ligase (LplA). Subsequently, existing analytic methods for the components and reactions of the GCS and recent advances in quantitatively understanding and purposefully engineering the GCS are presented. Finally, perspectives of current state of the art in the GCS research are given and future research needs are highlighted.