Structural Analysis of the Effect of Asn107Ser Mutation on Alg13 Activity and Alg13-Alg14 Complex Formation and Expanding the Phenotypic Variability of ALG13-CDG.

Karolina Mitusińska,Artur Góra,Anna Tylki-Szymańska,Agnieszka Rożdżyńska-Świątkowska,Aleksandra Jezela-Stanek,Anna Bogdańska

doi:10.3390/biom12030398

Karolina Mitusińska, Artur Góra + Show 4 more

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https://doi.org/10.3390/biom12030398

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Abstract

Congenital Disorders of Glycosylation (CDG) are multisystemic metabolic disorders showing highly heterogeneous clinical presentation, molecular etiology, and laboratory results. Here, we present different transferrin isoform patterns (obtained by isoelectric focusing) from three female patients harboring the ALG13 c.320A>G mutation. Contrary to other known variants of type I CDGs, where transferrin isoelectric focusing revealed notably increased asialo- and disialotransferrin fractions, a normal glycosylation pattern was observed in the probands. To verify this data and give novel insight into this variant, we modeled the human Alg13 protein and analyzed the dynamics of the apo structure and the complex with the UDP-GlcNAc substrate. We also modeled the Alg13-Alg14 heterodimer and ran multiple simulations of the complex in the presence of the substrate. Finally, we proposed a plausible complex formation mechanism.

Highlights

Congenital Disorders of Glycosylation (CDG) are multisystemic metabolic disorders caused by defects in N-linked, or O-linked oligosaccharides, shared substrates, glycophosphatidylinositol (GPI) anchors, or dolichols pathways [1]
The first part presents the transferrin isoform patterns of our three patients obtained by isoelectric focusing (IEF)
The two aims of our analyses were: (i) to present the differences in transferrin profiles noted in our patients with ALG13-CDG caused by c.320A>G, who presented with different clinical courses and (ii) to discuss the possible disease mechanism based on protein modeling

Summary

Introduction

Congenital Disorders of Glycosylation (CDG) are multisystemic metabolic disorders caused by defects in N-linked, or O-linked oligosaccharides, shared substrates, glycophosphatidylinositol (GPI) anchors, or dolichols pathways [1]. Type II CDGs are diagnosed when there are processing defects of the glycan in the ER or the Golgi apparatus. Considering ALG13-CDG, the c.320A>G (p.Asn107Ser) variant is by far the most frequent in affected female heterozygotes [7]. To date, it has been described in 46 females and only three males [2,4–7,9,10]. The details of the effect of this mutation on glycosylation process remains unknown. FoldX introduces the substitution(s) of the selected amino acid(s), optimizes the structure of a new variant, and calculates the difference in the Gibbs free energy of protein folding between the native protein and the mutant variants in kcal/mol. Assessment of the Effect of the Introduced Mutation. The PredictSNP [42] server was used to assess the effect of the Asn107Ser mutation. Each tool predicts the mutation results in terms of neutral or deleterious effects as well as provides a percentage of confidence of its predictions

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