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superpathway of GDP-mannose-derived O-antigen building blocks biosynthesis

General Background |FRAME: Lipopolysaccharides Lipopolysaccharides| (LPS) are a major component of the outer membrane of Gram-negative bacteria. While they are protecting the membrane from certain kinds of chemical attacks, they also induce a strong response from animal immune systems. Lipopolysaccharides can be conceptually divided into three parts: |FRAME: Lipid-A "lipid A"|, which anchors LPS into the membrane; core oligosaccharide, which contributes to membrane stability; and the |FRAME: O-Antigens O-antigen|, which is a polysaccharide that extends away from the cell surface. The composition of the O-antigen varies among different strains, but in general it consists of repeating oligosaccharide subunits made up of three to five sugars. At least 20 different sugars are known to occur, and many of these sugars are unique dideoxyhexoses that are rarely found elsewhere in nature. The variations in sugar content of the O-antigens contribute to the wide variety of antigenic types between species and even strains of Gram-negative bacteria. Gram-positive bacteria and Archaea do not have a lipopolysaccharide. Instead they possess the S-layer (surface layer) as a component of the cell envelope |CITS: [11742749][1938891]|. The S-layer is composed of a single layer of identical proteins or glycoproteins that form a two-dimensional, monomolecular crystalline array |CITS:[7934867]|. Structurally, S-layer glycoproteins from Gram-positive bacteria resemble the O-antigens of Gram-negative organisms, and often contain similar modified sugar building blocks |CITS: [11741945]|. About This Pathway A group of 6-deoxyhexoses, including |FRAME: CPD-13559|, |FRAME: CPD-15612|, |FRAME: CPD-13829|, |FRAME: CPD-9388|, |FRAME: CPD0-1107| and |FRAME: CPD-15615| are used as components of the O-anigen repeating units in lipopolysaccharides of certain Gram-negative bacteria and of the S-layer of some Gram-positive bacteria. All of these modified sugar residues are synthesized in a GDP nucleotide-activated form from |FRAME: GLC-6-P| via |FRAME: GDP-MANNOSE|. Mannose is produced in its 6-phosphate form by the isomerization of |FRAME:GLC-6-P| via |FRAME: FRUCTOSE-6P| This is achieved by the action of the ubiquitous |FRAME: EC-5.3.1.9|, which also participates in glycolysis, and the more specific |FRAME: EC-5.3.1.8| |CITS: [1846611]|. In order to produce the activated mannose donor |FRAME: GDP-MANNOSE| the 6-phosphate is first reconstructed as a 1-phosphate form, followed by the action of |FRAME: EC-2.7.7.13| |CITS:[GaoIntJMassSpec05] [8922954]|. Before |FRAME: GDP-MANNOSE| can be converted to the other sugars, it loses the the hydroxyl group connected to carbon 6 by the action of |FRAME: EC-4.2.1.47|, producing |FRAME: GDP-4-DEHYDRO-6-DEOXY-D-MANNOSE| |CITS: [14739333]|. This compound is the substrate for several different enzymes, including dehydrogenases, aminotransferases, and dehydratases, resulting in the production of the different modified 6-deoxysugars shown in this pathway.

from BIOCYC source record: META_PWY-7323
Type: pathway
Taxonomic scope
:
conserved biosystem
BSID:
907975

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