Calcium is not required for immulectin-2 binding, but protects the protein from proteinase digestion.
Mammalian C-type lectins are calcium-dependent carbohydrate-binding proteins. They serve as cell adhesion molecules in cell-cell interactions, or function as pattern-recognition receptors in innate immunity. Calcium is a direct ligand for carbohydrate binding in mammalian C-type lectins such as mannose-binding proteins and macrophage mannose receptor. In the tobacco hornworm Manduca sexta, a group of lectins named immulectins have been discovered. Each immulectin contains dual carbohydrate-recognition domains. Previously, we showed that immulectin-2 (IML-2) binds to a bacterial lipopolysaccharide, and agglutination of Escherichia coli cells by IML-2 is calcium dependent. In this study, we demonstrated that IML-2 bound to bacterial lipid A, smooth and rough mutants of lipopolysaccharide, lipoteichoic acid and peptidoglycan, as well as to fungal mannan and beta-1, 3-glucan (laminarin and curdlan). Binding of IML-2 to microbial components was calcium independent, and was increased by addition of spermine, a polyamine. In addition, plasma IML-2 bound to mannan-agarose independent of calcium. But trypsin digestion of IML-2 was inhibited in the presence of calcium. Our results suggest that calcium is not required for IML-2 binding but protects IML-2 from trypsin digestion.
Yu
Xiao-Qiang
XQ
Division of Cell Biology and Biophysics, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA. Yux@umkc.edu
Ma
Yukun
Y
D000371:Agglutination / Q000187:drug effects / Q000276:immunology; D000818:Animals; D002118:Calcium / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology*; D007113:Immunity, Innate / Q000187:drug effects / Q000276:immunology; D019476:Insect Proteins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D037181:Lectins, C-Type / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D008050:Lipid A / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D018402:Manduca / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects / Q000276:immunology; D014357:Trypsin / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism
D019476:Insect Proteins; D037181:Lectins, C-Type; D008050:Lipid A; C417733:immulectin-2 protein, Manduca sexta; D014357:Trypsin; D002118:Calcium