Abstract
Pseudoclostridium thermosuccinogenes and Hungateiclostridium thermocellum are being studied for their potential to contribute to a more sustainable bio-based economy. Both species were shown previously to rely on GTP or pyrophosphate instead of ATP as cofactors in specific reactions of central energy metabolism for reasons that are not well understood yet. Since it is often impossible to predict cofactor specificity from the primary protein structure, thirteen enzymes from P. thermosuccinogenes were cloned and heterologous expressed in Escherichia coli to assess the cofactor usage in vitro and paint a more complete picture of the cofactor usage in the central metabolism of P. thermosuccinogenes. The assays were conducted with heat-treated E. coli cell-free extract devoid of background activity to allow the quick assessment of a relatively large number of (thermophilic) enzymes. Selected enzymes were also purified to allow the determination of the enzyme kinetics for competing cofactors. Following the results of the glucokinase (GK), galactokinase, xylulokinase (XK), and ribokinase assays, it seems that phosphorylation of monosaccharides by and large is mainly GTP-dependent. Some possible implications of this relating to the adenylate/guanylate energy charge are discussed here. Besides the highly expressed pyrophosphate-dependent 6-phosphofructokinase, another 6-phosphofructokinase was found to be equally dependent on ATP and GTP, while no 6-phosphofructokinase activity could be demonstrated for a third. Both type I glyceraldehyde 3-phosphate dehydrogenases were found to be NAD+-dependent, and further, acetate kinase, isocitrate dehydrogenase, and three enzymes predicted to be responsible for the interconversion of phosphoenolpyruvate and pyruvate (i.e., pyruvate kinase; pyruvate, phosphate dikinase; phosphoenolpyruvate synthase), were also assessed.
Highlights
Pseudoclostridium thermosuccinogenes and Hungateiclostridium thermocellum, thermophilic bacteria belonging to the Hungateiclostridiaceae have been shown to rely on GTP and pyrophosphate (PPi), as well as the “typical” ATP in their central metabolism (Zhou et al, 2013; Koendjbiharie et al, 2018)
The constructs were initially transformed to E. coli DH5α
It was already known that GK and XK from P. thermosuccinogenes prefer GTP over ATP (Koendjbiharie et al, 2018)
Summary
Pseudoclostridium thermosuccinogenes and Hungateiclostridium thermocellum, thermophilic bacteria belonging to the Hungateiclostridiaceae have been shown to rely on GTP and pyrophosphate (PPi), as well as the “typical” ATP in their central metabolism (Zhou et al, 2013; Koendjbiharie et al, 2018). Both are being studied for their potential to contribute to the transition toward a more sustainable bio-based economy. In particular the characteristics of their complex central energy metabolism should be unraveled, as significant metabolic engineering will be required to improve production yields, rates, and titres (Nielsen and Keasling, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
