Yu Xiao-Qiang, Ma Yukun
Division of Cell Biology and Biophysics, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA.
Insect Biochem Mol Biol. 2006 Jun;36(6):505-16. doi: 10.1016/j.ibmb.2006.03.010. Epub 2006 Apr 7.
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.
哺乳动物C型凝集素是钙依赖性碳水化合物结合蛋白。它们在细胞间相互作用中充当细胞粘附分子，或在先天免疫中作为模式识别受体发挥作用。钙是哺乳动物C型凝集素（如甘露糖结合蛋白和巨噬细胞甘露糖受体）中碳水化合物结合的直接配体。在烟草天蛾曼陀罗中，已发现一组名为免疫凝集素的凝集素。每种免疫凝集素都包含双碳水化合物识别结构域。此前，我们表明免疫凝集素-2（IML-2）与细菌脂多糖结合，并且IML-2对大肠杆菌细胞的凝集作用是钙依赖性的。在本研究中，我们证明IML-2与细菌脂质A、脂多糖的光滑和粗糙突变体、脂磷壁酸和肽聚糖结合，以及与真菌甘露聚糖和β-1,3-葡聚糖（海带多糖和可德兰多糖）结合。IML-2与微生物成分的结合不依赖于钙，并且通过添加多胺精胺而增强。此外，血浆IML-2与甘露聚糖琼脂糖的结合不依赖于钙。但是在有钙的情况下，IML-2的胰蛋白酶消化受到抑制。我们的结果表明，IML-2结合不需要钙，但可保护IML-2免受胰蛋白酶消化。
