Laboratory of Mechanistic Glycobiology, Department of Chemistry, ‡Biotechnology Research Center, and §Department of Biological Sciences, Michigan Technological University , Houghton, Michigan 49931, United States.
Biochemistry. 2014 Jul 15;53(27):4445-54. doi: 10.1021/bi5001307. Epub 2014 Jul 3.
The glycan epitopes of natural and synthetic glycoconjugates exist as covalent attachments of well-defined inner structures or scaffolds. Macromolecules such as proteins, peptides, lipids, and saccharides and synthetic structures serve as scaffolds of glycoconjugates. It is generally perceived that the biological activities of glycoconjugates are determined mainly by the attached glycans, while the seemingly inert inner scaffolds play a passive role by providing physical support to the attached glycan epitopes. However, our data show that scaffolds actively influence lectin recognition and can potentially modulate lectin-mediated signaling properties of glycoconjugates. Through in vitro experiments, we found that the scaffolds significantly altered the thermodynamic binding properties of the covalently attached glycan epitopes. When a free glycan was attached to a scaffold, its lectin binding entropy became more positive. The level of positive entropic gain was dependent on the types of scaffolds tested. For example, protein scaffolds of glycoproteins were found to generate more positive entropy of binding than synthetic scaffolds. Certain scaffolds were found to have limiting effects on glycoconjugate affinity. We also found that scaffold-bearing glycans with a similar affinity or an identical valence demonstrated different kinetics of lattice formation with lectins, when the scaffold structures were different. Our data support the view that scaffolds of glycoconjugates (i) help the covalently attached glycans become more spontaneous in lectin binding and (ii) help diversify the lattice forming or cross-linking properties of glycoconjugates.
天然和合成糖缀合物的糖基表位作为具有明确内部结构或支架的共价连接存在。蛋白质、肽、脂质和糖等大分子以及合成结构作为糖缀合物的支架。人们普遍认为，糖缀合物的生物活性主要取决于附着的聚糖，而看似惰性的内部支架通过为附着的糖基表位提供物理支撑，起着被动的作用。然而，我们的数据表明，支架可以主动影响凝集素的识别，并有可能调节糖缀合物中凝集素介导的信号转导特性。通过体外实验，我们发现支架显著改变了共价连接的糖基表位的热力学结合特性。当游离聚糖附着到支架上时，其与凝集素的结合熵变得更加正值。正熵增益的水平取决于所测试的支架类型。例如，糖蛋白的蛋白质支架被发现比合成支架产生更大的结合熵。某些支架对糖缀合物的亲和力有限制作用。我们还发现，当支架结构不同时，具有相似亲和力或相同价态的带有支架的聚糖在与凝集素形成晶格时表现出不同的动力学。我们的数据支持以下观点：糖缀合物的支架 (i) 有助于共价连接的聚糖在与凝集素结合时更加自发，(ii) 有助于糖缀合物的晶格形成或交联性质多样化。
