Novel Insights into Selected Disease-Causing Mutations within the SLC35A1 Gene Encoding the CMP-Sialic Acid Transporter.

Bożena Szulc,Wojciech Wiertelak,Yelyzaveta Zadorozhna,Dorota Maszczak-Seneczko,Mariusz Olczak

doi:10.3390/ijms22010304

Bożena Szulc, Wojciech Wiertelak + Show 3 more

Open Access

https://doi.org/10.3390/ijms22010304

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Abstract

Congenital disorders of glycosylation (CDG) are a group of rare genetic and metabolic diseases caused by alterations in glycosylation pathways. Five patients bearing CDG-causing mutations in the SLC35A1 gene encoding the CMP-sialic acid transporter (CST) have been reported to date. In this study we examined how specific mutations in the SLC35A1 gene affect the protein’s properties in two previously described SLC35A1-CDG cases: one caused by a substitution (Q101H) and another involving a compound heterozygous mutation (T156R/E196K). The effects of single mutations and the combination of T156R and E196K mutations on the CST’s functionality was examined separately in CST-deficient HEK293T cells. As shown by microscopic studies, none of the CDG-causing mutations affected the protein’s proper localization in the Golgi apparatus. Cellular glycophenotypes were characterized using lectins, structural assignment of N- and O-glycans and analysis of glycolipids. Single Q101H, T156R and E196K mutants were able to partially restore sialylation in CST-deficient cells, and the deleterious effect of a single T156R or E196K mutation on the CST functionality was strongly enhanced upon their combination. We also revealed differences in the ability of CST variants to form dimers. The results of this study improve our understanding of the molecular background of SLC35A1-CDG cases.

Highlights

Cells present a remarkable diversity of glycan structures, all of which play important roles in mediating essential intra- and intercellular processes
In this work we demonstrated that HEK293T cells produce a broader range of sialylated glycolipids than CHO cells
While CHO cells are derived from an ovarian tissue, the HEK293T cell line displays some characteristics of neurons [62], which is relevant when taking into account the neurological symptoms experienced by SLC35A1-Congenital disorders of glycosylation (CDG) patients

Summary

Introduction

Cells present a remarkable diversity of glycan structures, all of which play important roles in mediating essential intra- and intercellular processes. Sialic acids comprise a group of charged 9-carbon backbone sugars, of which 5-N-acetylneuraminic acid (Neu5Ac) is the most abundant in humans These sugars occupy terminal positions of N- and O-glycans, glycosphingolipids and some GPI anchors and constitute essential components of surface glycoconjugates and secreted proteins. A prominent example is the polysialylation of the neural cell adhesion molecule (NCAM), which ensures proper trafficking of neural progenitors during brain development [11,12]. Such a diverse repertoire of functions makes sialic acids a important feature of cellular glycans

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