Structural analysis of naturally occurring sialic acids

Eggshell Membrane/Gellan Gum Composite Hydrogels with Increased Degradability, Biocompatibility, and Anti-Swelling Properties for Effective Regeneration of Retinal Pigment Epithelium

A gellan gum (GG) hydrogel must demonstrate a number of critical qualities—low viscosity, degradability, desirable mechanical properties, anti-swelling properties, and biocompatibility—in order to be regarded as suitable for retinal pigment epithelium (RPE) regeneration. In this study, we investigated whether the application of an eggshell membrane (ESM) to a GG hydrogel improved these critical attributes. The crosslinking of the ESM/GG hydrogels was most effectively reduced, when a 4 w/v% ESM was used, leading to a 40% less viscosity and a 30% higher degradation efficiency than a pure GG hydrogel. The compressive moduli of the ESM/GG hydrogels were maintained, as the smaller pores formed by the addition of the ESM compensated for the slightly weakened mechanical properties of the ESM/GG hydrogels. Meanwhile, due to the relatively low hydrophilicity of ESM, a 4 w/v% ESM enabled an ESM/GG hydrogel to swell 30% less than a pure GG hydrogel. Finally, the similarity in components between the ESM and RPE cells facilitated the proliferation of the latter without any significant cytotoxicity.

Complexity and Diversity of the Mammalian Sialome Revealed by Nidovirus Virolectins

Sialic acids (Sias), 9-carbon-backbone sugars, are among the most complex and versatile molecules of life. As terminal residues of glycans on proteins and lipids, Sias are key elements of glycotopes of both cellular and microbial lectins and thus act as important molecular tags in cell recognition and signaling events. Their functions in such interactions can be regulated by post-synthetic modifications, the most common of which is differential Sia-O-acetylation (O-Ac-Sias). The biology of O-Ac-Sias remains mostly unexplored, largely because of limitations associated with their specific in situ detection. Here, we show that dual-function hemagglutinin-esterase envelope proteins of nidoviruses distinguish between a variety of closely related O-Ac-Sias. By using soluble forms of hemagglutinin-esterases as lectins and sialate-O-acetylesterases, we demonstrate differential expression of distinct O-Ac-sialoglycan populations in an organ-, tissue- and cell-specific fashion. Our findings indicate that programmed Sia-O-acetylation/de-O-acetylation may be critical to key aspects of cell development, homeostasis, and/or function.

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Virolectins detect and distinguish between closely related O-Ac-Sias in situ

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O-Ac-sialoglycans occur in nature in a diversity not appreciated so far

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O-Ac-Sias are differentially expressed in a species-, tissue-, and cell-specific fashion

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There is extensive cell-to-cell variability in O-Ac-Sia expression in vivo and in vitro

Profiling of glycan receptors for minute virus of mice in permissive cell lines towards understanding the mechanism of cell recognition

The recognition of sialic acids by two strains of minute virus of mice (MVM), MVMp (prototype) and MVMi (immunosuppressive), is an essential requirement for successful infection. To understand the potential for recognition of different modifications of sialic acid by MVM, three types of capsids, virus-like particles, wild type empty (no DNA) capsids, and DNA packaged virions, were screened on a sialylated glycan microarray (SGM). Both viruses demonstrated a preference for binding to 9-O-methylated sialic acid derivatives, while MVMp showed additional binding to 9-O-acetylated and 9-O-lactoylated sialic acid derivatives, indicating recognition differences. The glycans recognized contained a type-2 Galβ1-4GlcNAc motif (Neu5Acα2-3Galβ1-4GlcNAc or 3′SIA-LN) and were biantennary complex-type N-glycans with the exception of one. To correlate the recognition of the 3′SIA-LN glycan motif as well as the biantennary structures to their natural expression in cell lines permissive for MVMp, MVMi, or both strains, the N- and O-glycans, and polar glycolipids present in three cell lines used for in vitro studies, A9 fibroblasts, EL4 T lymphocytes, and the SV40 transformed NB324K cells, were analyzed by MALDI-TOF/TOF mass spectrometry. The cells showed an abundance of the sialylated glycan motifs recognized by the viruses in the SGM and previous glycan microarrays supporting their role in cellular recognition by MVM. Significantly, the NB324K showed fucosylation at the non-reducing end of their biantennary glycans, suggesting that recognition of these cells is possibly mediated by the Lewis X motif as in 3′SIA-Le^X identified in a previous glycan microarray screen.