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Course: MCAT > Unit 2

Lesson 1: Foundation 1: Biomolecules

Enzyme study: PMM/PGM and its substrates


Nearly all Gram-negative bacteria possess lipopolysaccharide (LPS), an immunogenic molecule depicted in Figure 1. This structure is highly conserved across various microbes and plays a pivotal role in triggering the innate immune response in host organisms. When purified LPS is injected into experimental animals, it can induce endotoxic shock, often resulting in fatal outcomes.
Figure 1 Structure of LPS
The precursor of LPS is glucose-1-phosphate, which is formed when the enzyme phosphoglucomutase (PGM) rearranges glucose-6-phosphate. Conversely, PGM can also convert ample supplies of glucose-1-phosphate, sourced from glycogen, into glucose-6-phosphate—a fundamental molecule for both glycolysis and the pentose phosphate pathways. PGM has emerged as a potential target for antibacterial therapy due to its pivotal role; inhibiting PGM could disrupt LPS production and impede bacterial utilization of glucose-1-phosphate as an energy source.
In the Gram-negative bacterium P. aeruginosa, the enzyme phosphomannomutase/phosphoglucomutase (PMM/PGM) is essential for the biosynthesis of LPS and alginate, another molecule implicated in bacterial virulence. Phosphomannomutase (PMM) functionality rearranges mannose-6-phosphate into mannose-1-phosphate, a precursor of alginate, believed to encapsulate bacterial cells, shielding them from phagocytosis. PMM/PGM comprises four domains, three of which share a similar three-dimensional fold.
A team of researchers isolated the PMM/PGM enzyme through gel filtration and subjected it to analysis via SDS-PAGE. In Figure 2, lane 1 displays a standard protein ladder, lane 2 depicts the PMM/PGM sample before filtration, and lanes 3 to 5 depict sequential purifications of the enzyme."
Figure 2 Results of SDS PAGE analysis
Researchers also assessed the Km and Vmax values of the PMM/PGM enzyme for its substrates by Lineweaver-Burke analysis. Results are shown in Table 1.
Table 1 Kinetics of the bifunctional PMM/PGM enzyme
Sources: Ye, R. W., Zielinski, N. A., and Chakrabarty, A. M. (1994) Purification and characterization of phosphomannomutase/phosphoglucomutase from Pseudomonas aeruginosa involved in biosynthesis of both alginate and lipopolysaccharide, J Bacteriol 176, 4851-4857.
Where in the cell would LPS likely be found?
Choose 1 answer: