Division of Infectious Diseases, Department of Internal Medicine, Center for Microbial Interface Biology, The Ohio State University, Columbus, OH 43210, USA.
Glycobiology. 2009 Dec;19(12):1473-84. doi: 10.1093/glycob/cwp122. Epub 2009 Aug 16.
Surfactant protein D (SP-D), a lectin that recognizes carbohydrates via its C-type carbohydrate recognition domains (CRDs), regulates Mycobacterium tuberculosis (M.tb)-macrophage interactions via recognition of M.tb mannosylated cell wall components. SP-D binds to, agglutinates, and reduces phagocytosis and intracellular growth of M.tb. Species-specific variations in the CRD amino acid sequence contribute to carbohydrate recognition preferences and have been exploited to enhance the antimicrobial properties of SP-D in vitro. Here, we characterized the binding interaction between several wild-type and mutant SP-D neck + CRD trimeric subunits (NCRDs) and pathogenic and nonpathogenic mycobacterial species. Specific amino acid substitutions (i.e., the 343-amino-acid position) that flank the carbohydrate binding groove led to significant increases in binding of only virulent and attenuated M.tb strains and to a lesser extent M. marinum, whereas there was negligible binding to M. avium complex and M. smegmatis. Moreover, a nonconserved mutation at the critical 321-amino-acid position (involved in Ca(2+) coordination) abrogated binding to M.tb and M. marinum. We further characterized the binding of NCRDs to the predominant surface-exposed mannosylated lipoglycans of the M.tb cell envelope. Results showed a binding pattern that is dependent on the nature of the side chain of the 343-amino-acid position flanking the SP-D CRD binding groove and the nature of the terminal mannosyl sugar linkages of the mycobacterial lipoglycans. We conclude that the 343 position is critical in defining the binding pattern of SP-D proteins to M.tb and its mannosylated cell envelope components.
表面活性蛋白 D（SP-D）是一种通过 C 型碳水化合物识别结构域（CRD）识别碳水化合物的凝集素，通过识别分枝杆菌属细胞壁上甘露糖基化的成分来调节分枝杆菌属-巨噬细胞相互作用。SP-D 结合、聚集并减少分枝杆菌属的吞噬作用和细胞内生长。CRD 氨基酸序列中的种特异性变异导致碳水化合物识别偏好，并已被利用来增强 SP-D 在体外的抗菌特性。在这里，我们描述了几种野生型和突变型 SP-D 颈+CRD 三聚体（NCRD）与致病性和非致病性分枝杆菌属物种之间的结合相互作用。侧翼碳水化合物结合槽的特定氨基酸取代（即 343 位氨基酸）仅导致毒力和减毒分枝杆菌属菌株的结合显著增加，而对分枝杆菌属 marinum 的结合程度较小，而对鸟分枝杆菌属复合群和分枝杆菌属 smegmatis 的结合可以忽略不计。此外，关键 321 位氨基酸（参与 Ca(2+) 配位）的非保守突变导致与分枝杆菌属和分枝杆菌属 marinum 的结合丧失。我们进一步研究了 NCRD 与分枝杆菌属细胞外被的主要表面暴露的甘露糖基化糖脂的结合。结果显示，结合模式依赖于侧翼 SP-D CRD 结合槽的 343 位氨基酸的侧链的性质以及分枝杆菌属糖脂的末端甘露糖基连接的性质。我们得出结论，343 位是决定 SP-D 蛋白与分枝杆菌属及其甘露糖基化细胞外被成分结合模式的关键。
