GlgE (PP_4060) is a predicted maltosyltransferase that uses alpha-maltose 1-phosphate to extend alpha-1,4-glucan acceptors by two glucosyl residues, releasing phosphate. It is the polymer-elongating enzyme of a trehalose-derived branched alpha-glucan biosynthetic route with TreSB and GlgB.
Definition: Catalysis of the transfer of a maltosyl group from alpha-maltose 1-phosphate to the nonreducing end of an alpha-1,4-glucan, extending the acceptor by two glucosyl residues and releasing phosphate.
Justification: The exact EC 2.4.99.16/RHEA:42692 reaction transfers a maltosyl disaccharide, which is not represented precisely by the existing hexosyltransferase term.
Parent term: glycosyltransferase activity
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds | IEA GO_REF:0000002 | REMOVE | Summary: The GH13 fold mapping assigns hydrolysis, but the supported GlgE reaction transfers maltosyl units from maltose 1-phosphate to glucan. Reason: The net EC 2.4.99.16/RHEA:42692 reaction is a glycosyl transfer that releases phosphate, not hydrolysis of an O-glycosyl compound. This is a fold-level InterPro overextension and should not be propagated. Supporting Evidence: file:PSEPK/glgE/glgE-uniprot.txt Reaction=alpha-maltose 1-phosphate + [(1->4)-alpha-D-glucosyl](n) = |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: GlgE directly transforms carbohydrate substrates in alpha-glucan synthesis. Reason: This broad process is correct but adds little beyond the accepted alpha-glucan biosynthetic process and does not identify the reaction. Supporting Evidence: file:PSEPK/glgE/glgE-uniprot.txt involved in a branched alpha-glucan biosynthetic pathway |
| GO:0016757 glycosyltransferase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: GlgE is a glycosyltransferase, but this term is broader than its hexosyl transfer. Reason: The annotation has the correct reaction class but is redundant with the more informative GO:0016758 annotation. Supporting Evidence: file:PSEPK/glgE/glgE-uniprot.txt Maltosyltransferase that uses maltose 1-phosphate (M1P) |
| GO:0016758 hexosyltransferase activity | IEA GO_REF:0000104 | ACCEPT | Summary: GlgE transfers a maltosyl unit from maltose 1-phosphate to alpha-1,4-glucan. Reason: The HAMAP assignment specifies EC 2.4.99.16/RHEA:42692, GlgE-specific InterPro signatures, and binding sites for alpha-maltose 1-phosphate. GO lacks a substrate-specific GlgE molecular-function term. GO:0016758 is the most specific available annotation, although the reaction transfers a maltosyl disaccharide rather than a single hexosyl group. Supporting Evidence: file:PSEPK/glgE/glgE-uniprot.txt DR GO; GO:0016758; F:hexosyltransferase activity; IEA:UniProtKB-UniRule. file:PSEPK/glgE/glgE-uniprot.txt DR InterPro; IPR026585; GlgE. |
| GO:0030979 alpha-glucan biosynthetic process | IEA GO_REF:0000104 | ACCEPT | Summary: GlgE elongates alpha-1,4-glucan using maltose 1-phosphate. Reason: Polymer extension is a direct alpha-glucan biosynthetic reaction. This does not assign GlgE the TreSB precursor-generating or GlgB branching reactions. Supporting Evidence: file:PSEPK/glgE/glgE-uniprot.txt the sugar donor to elongate linear or branched alpha-(1->4)-glucans. |
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