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High-resolution structures reveal how a germline antibody can recognize a range of clinically relevant carbohydrate epitopes. The germline response to a carbohydrate immunogen can be critical to survivability, with selection for antibody gene segments that both confer protection against common pathogens and retain the flexibility to adapt to new disease organisms. We show here that antibody S25-2 binds several distinct inner-core epitopes of bacterial lipopolysaccharides (LPSs) by linking an inherited monosaccharide residue binding site with a subset of complementarity-determining regions (CDRs) of limited flexibility positioned to recognize the remainder of an array of different epitopes. This strategy allows germline antibodies to adapt to different epitopes while minimizing entropic penalties associated with the immobilization of labile CDRs upon binding of antigen, and provides insight into the link between the genetic origin of individual CDRs and their respective roles in antigen recognition.

Biodegradation of hemicelluloses requires enzyme activities that remove nonxylose substituents from the xylan backbone in addition to endoxylanases and β-xylosidases. Activities removing o-acetyl, arabinose, cinnamic acid-based esters, and uronic acid substituents occurred inStreptomyces olivochromogenes, Aspergillus niger, andSchizophyllum commune. 4-O-Methylglucuronidase was coinduced with other substituent-hydrolyzing enzymes when appropriate lignocellulosic materials were provided. Fractionation of crude enzymes indicated that the 4-o-methylglucuronidases were polydisperse. The 4-o-methylglucuronidases fromS. commune andA. niger acted on high molecular weight heteroxylans, but those from S.olivochromogenes functioned only with small, endo-β-(1,4)-xylanse-solubilized fragments.