Lectin-carbohydrate interactions: fine specificity difference between two mannose-binding proteins.
Two types of rat mannose-binding proteins (MBPs), MBP-A (serum type) and MBP-C (liver type), have similar binding specificity for monosaccharide and similar binding site construct according to the X-ray structure, but exhibit different affinity toward natural oligosaccharides and glycoproteins. To understand the basis for this phenomenon, we used cloned fragment of MBP-A and -C (entire carbohydrate-recognition domain and a short connecting piece) that exists as stable trimers in various binding studies. Binding of a number of mannose-containing di- and tri-saccharides and high-mannose type oligosaccharides indicated that MBP-C has an extended binding area of weak interaction with the second and the third mannose residues, whereas MBP-A recognizes just a single mannose residue. In addition, MBP-C has a weak secondary binding site some 25 A away from the primary site. These findings explain the higher affinity of MBP-C for natural high-mannose type oligosaccharides as compared to MBP-A. A huge affinity differential manifested by natural glycoproteins (e.g., inhibitory potency of thyroglobulin is approximately 200 fold higher for MBP-C than for MBP-A in a solid-phase assay) may be due to steric hindrance experienced by MBP-A in the competition assay, and suggests different arrangement of subunit in the MBP trimers.
Lee
R T
RT
Department of Biology, The Johns Hopkins University, Baltimore, MD 21218, USA. reiko.lee@jhu.edu
Shinohara
Y
Y
Hasegawa
Y
Y
Lee
Y C
YC
D000818:Animals; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D002240:Carbohydrate Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D018360:Crystallography, X-Ray; D020128:Inhibitory Concentration 50; D007700:Kinetics; D037102:Lectins / Q000378:metabolism*; D037601:Mannose-Binding Lectin; D008956:Models, Chemical; D008969:Molecular Sequence Data; D011487:Protein Conformation; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors
D002352:Carrier Proteins; D037102:Lectins; D037601:Mannose-Binding Lectin; C445599:Mbl2 protein, rat; D011994:Recombinant Proteins; C069858:mannose binding protein A