bims-meglyc 2026-07-12 papers

HGG Adv. 2026 Jul 08. pii: S2666-2477(26)00090-4. [Epub ahead of print] 100650

ALG14 Variants Contribute to a Congenital Disorder of Glycosylation Characterized by Congenital Myasthenia and Epilepsy.

Asparagine-linked glycosylation 14 (ALG14) is a UDP-GlcNAc transferase that catalyzes the second sugar addition in the synthesis of the dolichol-linked oligosaccharide precursor in N-linked glycosylation, ultimately contributing to glycosylation of a wide array of proteins. Biallelic pathogenic variants in ALG14 have been suggested to lead to a congenital disorder of glycosylation (CDG) due to incomplete lipid linked oligosaccharide synthesis and ultimately hypoglycosylation of N-linked glycoproteins. In a cohort of nine previously unreported individuals with bi-allelic variants in ALG14 from eight unrelated families we demonstrate evidence of a CDG that manifests as a congenital myasthenic syndrome, epilepsy, joint contractures, and dysmorphic features. Using a Xenopus knockdown model of disease, we explored the ramifications of alg14 depletion on early neurodevelopment and used this model as a platform to test the function of previously identified ALG14 missense variants as well as missense variants from the individuals reported in this study. Investigations of the Xenopus model tissue and tissue from an affected individual elucidated a mechanism by which dysfunctional glycosylation may lead to neurological disease and establish this as a Bona fide CDG. These findings may guide evaluation of future individuals with suspected ALG14-CDG and future targeted therapeutics such as those being used in other CDG.

DOI: https://doi.org/10.1016/j.xhgg.2026.100650

J Lipid Res. 2026 Jul 09. pii: S0022-2275(26)00132-X. [Epub ahead of print] 101102

B4GALT5 deficiency impairs glycosphingolipid biosynthesis: a new Congenital Disorder of Glycosylation?

Linda Montavoci, Michele Dei Cas, Anna Caretti, Omar Ben Mariem, Ivano Eberini, Laura Giaquinto, Alessandro De Falco, Maria Antonietta de Matteis, Nicola Brunetti-Pierri, Marco Trinchera.

Lactosylceramide is a glycosphingolipid precursor synthesized by two dedicated galactosyltransferases, B4GALT5 and B4GALT6. The specific roles of B4GALT5 and B4GALT6 in humans have not yet been clearly defined. Here, we report the first human case with bi-allelic loss-of-function variants in B4GALT5, suggesting that intact B4GALT5 activity is indispensable for normal glycosphingolipid biosynthesis and human development. We identified bi-allelic variants in the B4GALT5 gene in a child presenting with microcephaly, mild cognitive impairment, and bilateral cataracts. B4GALT5/6 double KO cells transfected with B4GALT5 carrying either of the variants identified in the patient lacked lactosylceramide synthase activity and failed to produce glycosphingolipids. In-silico analyses predicted decreased protein stability and impaired UDP-Gal binding for both B4GALT5 variants. Together, these findings indicate that both variants result in deficient B4GALT5 activity, leaving B4GALT6 as the sole source of lactosylceramide synthase activity. Consistent with this, patient plasma and fibroblasts exhibited an approximately 80% reduction in glycosphingolipid levels compared with healthy controls. Unexpectedly, when expressed in model cells human B4GALT6 displayed lower expression and lower catalytic activity, than human B4GALT5, raising questions about its capacity to compensate for B4GALT5 deficiency. In conclusion, we identified a potential new congenital disorder of glycosylation caused by deficient lactosylceramide synthase activity that may be insufficient to support glycosphingolipids synthesis at levels required for normal brain function.

Keywords: CRISPR-Cas9 genome editing; brain lipids; fluorescence microscopy; galactosyltransferase; glycolipids; homology modeling; intellectual disability; lactosylceramide synthase; lipidomics; sphingolipids

DOI: https://doi.org/10.1016/j.jlr.2026.101102

J Biomol Struct Dyn. 2026 Jul 07. 1-14

Structural insights into mutated human phosphoglucomutase 1 (PGM1) using computational approaches.

Eman Abdullah Almuqri.

The phosphoglucomutase 1 (PGM1) enzyme plays a critical role in metabolism and glycosylation in the human body. PGM1 has been linked to multiple disease phenotypes, including the inherited metabolic disorder known as congenital disorders of glycosylation (CDGs). Numerous clinical studies have shown that mutations in key regions of the PGM1 gene affect catalytic activity and induce folding defects of the enzyme. To delve into molecular changes at the supramolecular level, the structural, stability, and other features of PGM1 variants (T19A, N38Y, and D62H) were studied in the present work. To this end, molecular dynamics (MD) simulation at a long timescale (500 ns) was carried out. Parameters such as root-mean-square deviation (RMSD), root-mean-square fluctuations (RMSF), radius of gyration (Rg), solvent-accessible surface area (SASA), hydrogen bonds, and free energy landscape (FEL) were studied and compared with those of the wild-type PGM1. It was noted that mutations 19 A, N38Y, and D62H significantly alter the protein's structural behavior, causing increased flexibility, reduced stability, and compactness.

Keywords: Free energy landscape; MD simulation; Phosphoglucomutase 1; Protein structural stability; Variants

DOI: https://doi.org/10.1080/07391102.2026.2696958

Protein Sci. 2026 Aug;35(8): e70715

Mechanism-guided mutagenesis of Rft1 to test its role as a dolichol-linked oligosaccharide scramblase in cells.

George N Chiduza, Ken-Taro Sakata, Hannah G Wolfe, Faria Noor, Anant K Menon.

The membrane protein Rft1 is proposed to play an essential role in yeast and human cells by scrambling the glycolipid Man5GlcNAc2-PP-dolichol (M5-DLO) across the endoplasmic reticulum (ER) for protein N-glycosylation. While this activity has been demonstrated in liposomes reconstituted with purified Rft1, biochemical evidence of additional M5-DLO scramblases and the viability of Rft1-null Trypanosoma brucei suggest that scrambling may be a moonlighting function of Rft1 rather than its essential cellular role. To investigate this problem, we used AlphaFold3 and Chai-1 to model the conformational dynamics of yeast Rft1-M5-DLO complexes. The models suggest an alternating access mechanism, typical of Multidrug/Oligosaccharidyl-lipid/Polysaccharide (MOP) superfamily transporters, in which a cationic central cavity coordinates the anionic headgroup of M5-DLO, while the dolichol tail of the lipid is accommodated through a lateral portal formed by two transmembrane helices. We used the models to design mutations to disrupt the interaction between Rft1 and the M5-DLO headgroup, and to engineer a salt bridge to block the portal and stall transport. Using a Tet-off yeast reporter strain, we tested 26 central cavity mutants and identified 2 that supported cell growth poorly despite being well-expressed. Strikingly, the portal-blocking mutant which is predicted to lack scramblase activity supported robust growth. These data suggest that while M5-DLO binding is important for Rft1's essential function, scrambling activity is dispensable. We speculate that Rft1's essential role may be as an M5-DLO chaperone, capturing and routing M5-DLO propitiously on the cytoplasmic side of the ER to coordinate DLO biosynthesis.

Keywords: AlphaFold3; Chai‐1; M5‐DLO; MOP transporter superfamily; N‐glycosylation; alternating‐access; chaperone; congenital disorder of glycosylation; flippase; protein structure prediction

DOI: https://doi.org/10.1002/pro.70715