| Description | The E. coli O113 antigen monomer [1] consists of a branched pentasaccharide of relatively simple galactose and glucose-derived units: [->4)aDGalNAc{(3<-1)bDGal}(1->4)aDGalA(1->3)aDGal(1->3)bDGlcNAc(1->]. Additionally, there is some degree of O-acetylation, the position and extent of which has not yet been determined. The biosynthesis cluster contains four corresponding glycosyltransferases, WbnABDE. Assignments of activity have been predicted at ECODAB, but are not as strong as some and may be in error. These are based on the following homology data and logic: Of the four, WbnE has the strongest similarity to other known enzymes, in the range 37-46% identity, the top four of which are all predicted to carry out the aDGal(1->3)bDGlcNAc reaction. WbnA has the next strongest similarities, in the range 33-37% identity, and although the reactions predicted to be carried out by these homologs are similar to both the aDGalNAc(1->4)aDGalA and the aDGalNAc{(3<-1)bDGal} reactions, one homolog carries out precisely the former reaction and has been experimentally confirmed. Of the remaining two transferases, WbnB and WbnD, both of which show similarities to other glycosyltransferases only in the 26-29% identity range, the correlation between the homologs activities and the ones needed in the O113 cluster are weak and ambiguous. So although ECODAB makes predictions, we do not regard them as sufficiently strong to drive transitive annotations. |
