title: Engineering galactose-binding activity into a C-type mannose-binding protein.
abstract: Calcium-dependent or C-type carbohydrate-recognition domains are homologous protein modules found in a variety of animal lectins. Selective binding of sugars by these domains is essential for glycoprotein clearance, cell-cell adhesion and pathogen neutralization. Although various C-type carbohydrate-recognition domains share sequence identity ranging from 20 to 55%, their sugar-binding characteristics vary widely. The structure of a mannose-binding carbohydrate-recognition domain in complex with a saccharide ligand suggests that two glutamic acid-asparagine pairs are essential determinants of ligand binding by this domain. In C-type lectins that bind galactose with higher affinity than mannose, one of these pairs is replaced by glutamine-aspartic acid. Here we shift the sequence of the mannose-binding protein to correspond to that found in galactose-binding domains in order to test the importance of these residues in sugar-binding selectivity. This simple switch in the position of a single amide group alters the binding activity of the domain so that galactose becomes the preferred ligand.
mesh_terms: D000116:Acetylgalactosamine / Q000378:metabolism; D000117:Acetylglucosamine / Q000378:metabolism; D000209:Acute-Phase Proteins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005643:Fucose / Q000378:metabolism; D005690:Galactose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D008358:Mannose / Q000378:metabolism; D037241:Mannose-Binding Lectins; D008969:Molecular Sequence Data; D015202:Protein Engineering; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D006023:Glycoproteins; D037241:Mannose-Binding Lectins; D005643:Fucose; D005947:Glucose; D000116:Acetylgalactosamine; D008358:Mannose; D000117:Acetylglucosamine; D005690:Galactose