Alpha-D-phosphohexomutase | |
---|---|
Identifiers | |
Symbol | PGM_I-III |
Pfam clan | CL0754 |
ECOD | 7528.1.1 |
InterPro | IPR016055 |
CDD | cd03084 |
The alpha-D-phosphohexomutases are a large superfamily of enzymes, with members in all three domains of life. Enzymes from this superfamily are ubiquitous in organisms from E. coli to humans, and catalyze a phosphoryl transfer reaction on a phosphosugar substrate. Four well studied subgroups in the superfamily are:
Other enzymes in the superfamily are known to act as glucose 1,6-bisphosphate synthases and phosphopentomutases.
A number of proteins in the superfamily have been characterized functionally and structurally. This table illustrates different members of the superfamily.
The enzymes in the superfamily typically catalyze the reversible conversion of 1-phosphosugars to 6-phosphosugars. The reaction proceeds via a bisphosphorylated sugar intermediate. The active form of the enzyme is phosphorylated at a conserved serine residue in the active site, and also requires a bound metal ion, typically Mg2+ for full activity. The initial phosphoryl transfer takes place from the phosphoserine to the substrate, creating a bisphosphorylated sugar intermediate. This is followed by a second phosphoryl transfer from the substrate back to enzyme, producing product and regenerating the active form of the enzyme. [36]
Structures of multiple enzymes have been determined through X-ray crystallography. In general, they share a very similar topology. With a heart-shape and four domains (see image below), most enzymes appear to be monomers.
However some are known to exist as dimers or tetramers in solution. Eleven crystal structures for this superfamily have been determined thus far, six of which are likely oligomers. Two distinct dimers and one tetrameric arrangement has been documented. [37]
There are 4 well characterized enzyme subgroups in this superfamily, which differ in their specificity for the sugar moiety of the substrate.
Phosphoglucomutase (PGM) converts D-glucose-1-phosphate into D-glucose-6-phosphate, participating in glucose breakdown & synthesis. Bacterial and eukaryotic organisms are known to have PGM enzymes, with 415 representatives currently listed in the PIR database. [38] Among bacteria, Salmonella typhimurium and Thermus thermophilus have PGM enzymes of characterized 3D structure. In eukaryotes, PGM enzymes from Oryctolagus cuniculus (rabbit) and Paramecium tetraurelia also have been structurally characterized. The highest resolution structure is from Salmonella typhimurium (1.7 A), with PDB ID 3na5. In addition, biochemical studies have shown that PGM from S. typhimurium is a dimer in solution based on analytical ultracentrifugation and small-angle X-ray scattering (SAXS). [39]
Phosphoglucomutase/phosphomannomutase (PGM/PMM)- Enzymes from this subgroup can use either mannose or glucose-based phosphosugar substrates with equal efficiency. PMM/PGM enzymes are found mainly in bacterial organisms, with a total of 1,331 representatives currently listed in the PIR database. [40] These enzymes are involved in the biosynthesis of many different carbohydrates and glycolipids, which vary depending on the organism. The best studied enzyme from this subgroup is from the bacterium, Pseudomonas aeruginosa , where PMM/PGM participate in multiple biosynthetic pathways including those of lipopolysaccharide, alginate and rhamnolipid.
Structural studies of P. aeruginosa PMM/PGM by X-ray crystallography have been conducted as both apo-enzyme and as protein-ligand complexes. Based on these studies, it has been seen that when the sugar substrate binds to the enzyme there is a rotation in the C-terminal domain of the protein. This changes the active site from an open cleft in the apo-enzyme into a nearly solvent inaccessible pocket. This theme of conformational flexibility, particularly with regard to the C-terminal domain of these enzymes, has been observed in multiple proteins in the superfamily.
Phosphoglucosamine mutase (PNGM) participates in the biosynthesis of UDP-N-acetylglucosamine (UDP-GlcNAc). This bacterial enzyme has been conserved throughout evolution and is involved in the cytoplasmic steps of peptidoglycan biosynthesis, which is essential for bacterial survival and is also not present in humans. [41]
Phosphoacetylglucosamine mutase (PAGM)- To date, this subgroup contains 178 members, with all known being eukaryotic. [42] There is only one known organism with known structure, it is Candida albicans . Like PNGM, it is involved in the biosynthesis of UDP-N-acetylglucosamine. UDP-GlcNAc is a UDP sugar that works as a biosynthetic precursor of glycoproteins, mucopolysaccharides, and the cell wall of bacteria. AGM1, a characterized structure of PAGM, catalyzes the conversion of N-acetylglucosamine 6-phosphate to N-acetylglucosamine 1-phosphate. AGM1 structure was determined from Candida albicans in the apoform and complex forms with substrate and product. Like other enzymes in the superfamily, it has four domains, with two additional beta-strands in domain four and a circular permutation in domain 1. [43]
Autolysins are endogenous lytic enzymes that break down the peptidoglycan components of biological cells which enables the separation of daughter cells following cell division. They are involved in cell growth, cell wall metabolism, cell division and separation, as well as peptidoglycan turnover and have similar functions to lysozymes.
Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic member of the genus Streptococcus. S. pneumoniae cells are usually found in pairs (diplococci) and do not form spores and are non motile. As a significant human pathogenic bacterium S. pneumoniae was recognized as a major cause of pneumonia in the late 19th century, and is the subject of many humoral immunity studies.
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Aspergillus fumigatus is a species of fungus in the genus Aspergillus, and is one of the most common Aspergillus species to cause disease in individuals with an immunodeficiency.
Pseudomonas aeruginosa is a common encapsulated, Gram-negative, aerobic–facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, P. aeruginosa is a multidrug resistant pathogen recognized for its ubiquity, its intrinsically advanced antibiotic resistance mechanisms, and its association with serious illnesses – hospital-acquired infections such as ventilator-associated pneumonia and various sepsis syndromes. P. aeruginosa is able to selectively inhibit various antibiotics from penetrating its outer membrane - and has high resistance to several antibiotics. According to the World Health Organization P. aeruginosa poses one of the greatest threats to humans in terms of antibiotic resistance.
Virulence factors are cellular structures, molecules and regulatory systems that enable microbial pathogens to achieve the following:
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Rhodococcus equi is a Gram-positive coccobacillus bacterium. The organism is commonly found in dry and dusty soil and can be important for diseases of domesticated animals. The frequency of infection can reach near 60%. R. equi is an important pathogen causing pneumonia in foals. Since 2008, R. equi has been known to infect wild boar and domestic pigs. R. equi can infect immunocompromised people, such as HIV-AIDS patients or organ transplant recipients. Rhodococcus equi infection in these populations resemble the clinical and pathological signs of advanced pulmonary tuberculosis. This organism is a facultative intracellular mycobacterial pathogen.
Aerobactin is a bacterial iron chelating agent (siderophore) found in E. coliand other Enterobacteriaceae species. It is a virulence factor enabling E. coli to sequester iron in iron-poor environments such as the urinary tract.
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Streptococcus dysgalactiae is a gram positive, beta-haemolytic, coccal bacterium belonging to the family Streptococcaceae. It is capable of infecting both humans and animals, but is most frequently encountered as a commensal of the alimentary tract, genital tract, or less commonly, as a part of the skin flora. The clinical manifestations in human disease range from superficial skin-infections and tonsillitis, to severe necrotising fasciitis and bacteraemia. The incidence of invasive disease has been reported to be rising. Several different animal species are susceptible to infection by S. dysgalactiae, but bovine mastitis and infectious arthritis in lambs have been most frequently reported.
Sortase refers to a group of prokaryotic enzymes that modify surface proteins by recognizing and cleaving a carboxyl-terminal sorting signal. For most substrates of sortase enzymes, the recognition signal consists of the motif LPXTG (Leu-Pro-any-Thr-Gly), then a highly hydrophobic transmembrane sequence, followed by a cluster of basic residues such as arginine. Cleavage occurs between the Thr and Gly, with transient attachment through the Thr residue to the active site Cys residue, followed by transpeptidation that attaches the protein covalently to cell wall components. Sortases occur in almost all Gram-positive bacteria and the occasional Gram-negative bacterium or Archaea, where cell wall LPXTG-mediated decoration has not been reported. Although sortase A, the "housekeeping" sortase, typically acts on many protein targets, other forms of sortase recognize variant forms of the cleavage motif, or catalyze the assembly of pilins into pili.
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In molecular biology, the FasX small RNA (fibronectin/fibrinogen-binding/haemolytic-activity/streptokinase-regulator-X) is a non-coding small RNA (sRNA) produced by all group A Streptococcus. FasX has also been found in species of group D and group G Streptococcus. FasX regulates expression of secreted virulence factor streptokinase (SKA), encoded by the ska gene. FasX base pairs to the 5' end of the ska mRNA, increasing the stability of the mRNA, resulting in elevated levels of streptokinase expression. FasX negatively regulates the expression of pili and fibronectin-binding proteins on the bacterial cell surface. It binds to the 5' untranslated region of genes in the FCT-region in a serotype-specific manner, reducing the stability of and inhibiting translation of the pilus biosynthesis operon mRNA by occluding the ribosome-binding site through a simple Watson-Crick base-pairing mechanism.
D-glycero-beta-D-manno-heptose 1-phosphate adenylyltransferase is an enzyme with systematic name ATP:D-glycero-beta-D-manno-heptose 1-phosphate adenylyltransferase. This enzyme catalyses the following chemical reaction
C5a peptidase is an enzyme. The primary cleavage site is at His67-Lys68 in human C5a with a minor secondary cleavage site at Ala58-Ser59.
Cyclic di-AMP is a second messenger used in signal transduction in bacteria and archaea. It is present in many Gram-positive bacteria, some Gram-negative species, and archaea of the phylum Euryarchaeota.
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Virginia L. Miller is a microbiologist known for her work on studying the factors leading to disease caused by bacteria. Miller is an elected fellow of the American Academy of Microbiology (2003) and a former Pew Charitable Trust Biomedical Scholar (1989).
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