Impact of sialic acids on the molecular dynamic of bi-antennary and tri-antennary glycans (original) (raw)

Sialic acids (SA) are monosaccharides that can be located at the terminal position of glycan chains on a wide range of proteins. The post-translational modifications, such as N-glycan chains, are fundamental to protein functions. Indeed, the hydrolysis of SA by specific enzymes such as neuraminidases can lead to drastic modifications of protein behavior. However, the relationship between desialylation of N-glycan chains and possible alterations of receptor function remains unexplored. Thus, the aim of the present study is to establish the impact of SA removal from N-glycan chains on their conformational behavior. We therefore undertook an in silico investigation using molecular dynamics to predict the structure of an isolated glycan chain. We performed, for the first time, 3 independent 500 ns simulations on bi-antennary and tri-antennary glycan chains displaying or lacking SA. We show that desialylation alters both the preferential conformation and the flexibility of the glycan chain. This study suggests that the behavior of glycan chains induced by presence or absence of SA may explain the changes in the protein function. Sialic acids (SA) are electronegatively charged monosaccharides in higher animals and some microorganisms. They contribute to the wide structural diversity of complex carbohydrates, which are major constituents of most proteins and lipids of cell membranes and secreted macromolecules 1. SA are prominently positioned, usually at the outer end of these molecules. The diversity of glycan chains is even more increased by the biosynthesis of various kinds of SA. In human, the number of SA types is limited, with N-acetylneuraminic acid (Neu5Ac) prevailing and followed by derivatives which are O-acetylated and O-lactylated at the SA side chain 2. The external position of SA on glycoproteins, either alone or in oligo-or polymeric form, implies a strong influence in cell biology. Indeed, these acidic monosaccharides may easily interact with components at other cell surfaces, extracellular substances and effector molecules. Evidence is increasing that they are involved in a multiplicity of cell signalling events. For instance, we have shown previously that the desialylation of the insulin receptor by the neuraminidase-1 sialidase induces the dysregulation of cell glucose uptake and develops insulin resistance 3,4. Moreover, the desialylation of receptors such as PDGF-R or IGF-R alters cell proliferation 5. In the literature, several authors suppose that SA function is either to mask recognition sites 6 , or, contrarily, to act as a biological target that allows recognition by a receptor protein 7,8. However, the molecular process which leads to receptor alteration after the removal of SA is still unknown. The multiple combinations of glycan chain and the technical limitation of in vitro approaches are a crucial bottleneck to the understanding of SA function. This is even more complicated by the fact that the environment of these monosaccharides and the nature of the molecule to which they are bound may influence their biological effects. The aim of the present study is to characterize by molecular dynamics the behaviour of a single N-glycan chain detached from its protein, associated or not with SA. To our knowledge, this strategy has never been used and allows us to predict the stereotypic behaviour modifications