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Chemphyschem : a European Journal of... Dec 2023The catalytic mechanism of a -dependent family 92 -mannosidase, which is abundantly present in human gut flora and malfunctions leading to the lysosomal storage...
The catalytic mechanism of a -dependent family 92 -mannosidase, which is abundantly present in human gut flora and malfunctions leading to the lysosomal storage disease α-mannosidosis, has been investigated using quantum mechanics/molecular mechanics and metadynamics methods. Computational efforts show that the enzyme follows a conformational itinerary of and the ion serves a dual purpose, as it not only distorts the sugar ring but also plays a crucial role in orchestrating the arrangement of catalytic residues. This orchestration, in turn, contributes to the facilitation of conformers for the ensuing reaction. This mechanistic insight is well-aligned with the experimental predictions of the catalytic pathway, and the computed energies are of the same order of magnitude as the experimental estimations. Hence, our results extend the mechanistic understanding of glycosidases.
Topics: Catalysis; Mannosidases; Molecular Conformation; Molecular Dynamics Simulation; Gastrointestinal Microbiome; alpha-Mannosidosis; Bacterial Proteins
PubMed: 37782219
DOI: 10.1002/cphc.202300628 -
Genes Aug 2023A 7-month-old Doberman Pinscher dog presented with progressive neurological signs and brain atrophy suggestive of a hereditary neurodegenerative disorder. The dog was...
A Homozygous Missense Mutation in a Doberman Pinscher Dog with Neurodegeneration, Cytoplasmic Vacuoles, Autofluorescent Storage Granules, and an α-Mannosidase Deficiency.
A 7-month-old Doberman Pinscher dog presented with progressive neurological signs and brain atrophy suggestive of a hereditary neurodegenerative disorder. The dog was euthanized due to the progression of disease signs. Microscopic examination of tissues collected at the time of euthanasia revealed massive accumulations of vacuolar inclusions in cells throughout the central nervous system, suggestive of a lysosomal storage disorder. A whole genome sequence generated with DNA from the affected dog contained a likely causal, homozygous missense variant in that predicted an Asp104Gly amino acid substitution that was unique among whole genome sequences from over 4000 dogs. A lack of detectable α-mannosidase enzyme activity confirmed a diagnosis of a-mannosidosis. In addition to the vacuolar inclusions characteristic of α-mannosidosis, the dog exhibited accumulations of autofluorescent intracellular inclusions in some of the same tissues. The autofluorescence was similar to that which occurs in a group of lysosomal storage disorders called neuronal ceroid lipofuscinoses (NCLs). As in many of the NCLs, some of the storage bodies immunostained strongly for mitochondrial ATP synthase subunit c protein. This protein is not a substrate for α-mannosidase, so its accumulation and the development of storage body autofluorescence were likely due to a generalized impairment of lysosomal function secondary to the accumulation of α-mannosidase substrates. Thus, it appears that storage body autofluorescence and subunit c accumulation are not unique to the NCLs. Consistent with generalized lysosomal impairment, the affected dog exhibited accumulations of intracellular inclusions with varied and complex ultrastructural features characteristic of autophagolysosomes. Impaired autophagic flux may be a general feature of this class of disorders that contributes to disease pathology and could be a target for therapeutic intervention. In addition to storage body accumulation, glial activation indicative of neuroinflammation was observed in the brain and spinal cord of the proband.
Topics: Animals; Dogs; alpha-Mannosidase; alpha-Mannosidosis; Lysosomal Storage Diseases; Lysosomes; Mutation, Missense; Vacuoles; Neurodegenerative Diseases
PubMed: 37761886
DOI: 10.3390/genes14091746 -
American Journal of Medical Genetics.... May 2024Alpha-mannosidosis is a rare autosomal recessive lysosomal storage disorder caused by biallelic mutations in the MAN2B1 gene and characterized by a wide clinical...
Alpha-mannosidosis is a rare autosomal recessive lysosomal storage disorder caused by biallelic mutations in the MAN2B1 gene and characterized by a wide clinical heterogeneity. Diagnosis for this multisystemic disorder is confirmed by the presence of either a deficiency in the lysosomal enzyme acid alpha-mannosidase or biallelic mutations in the MAN2B1 gene. This diagnosis confirmation is crucial for both clinical management and genetic counseling purposes. Here we describe a late diagnosis of alpha-mannosidosis in a patient presenting with syndromic intellectual disability, and a rare retinopathy, where reverse phenotyping played a pivotal role in interpreting the exome sequencing result. While a first missense variant was classified as a variant of uncertain significance, the phenotype-guided analysis helped us detect and interpret an in-trans apparent alu-element insertion, which appeared to be a copy number variant (CNV) not identified by the CNV caller. A biochemical analysis showing abnormal excretion of urinary mannosyloligosaccharide and an enzyme assay permitted the re-classification of the missense variant to likely pathogenic, establishing the diagnosis of alpha-mannosidosis. This work emphasizes the importance of reverse phenotyping in the context of exome sequencing.
Topics: Humans; alpha-Mannosidosis; DNA Copy Number Variations; alpha-Mannosidase; Mutation, Missense; Phenotype
PubMed: 38192009
DOI: 10.1002/ajmg.a.63532 -
Gene Jan 2024A 6-month-old cat of unknown ancestry presented for a neurologic evaluation due to progressive motor impairment. Complete physical and neurologic examinations suggested...
A 6-month-old cat of unknown ancestry presented for a neurologic evaluation due to progressive motor impairment. Complete physical and neurologic examinations suggested the disorder was likely to be hereditary, although the signs were not consistent with any previously described inherited disorders in cats. Due to the progression of disease signs including severely impaired motor function and cognitive decline, the cat was euthanized at approximately 10.5 months of age. Whole genome sequence analysis identified a homozygous missense variant c.2506G > A in MANBA that predicts a p.Gly836Arg alteration in the encoded lysosomal enzyme β -mannosidase. This variant was not present in the whole genome or whole exome sequences of any of the 424 cats represented in the 99 Lives Cat Genome dataset. β -Mannosidase enzyme activity was undetectable in brain tissue homogenates from the affected cat, whereas α-mannosidase enzyme activities were elevated compared to an unaffected cat. Postmortem examination of brain and retinal tissues revealed massive accumulations of vacuolar inclusions in most cells, similar to those reported in animals of other species with hereditary β -mannosidosis. Based on these findings, the cat likely suffered from β -mannosidosis due to the abolition of β -mannosidase activity associated with the p.Gly836Arg amino acid substitution. p.Gly836 is located in the C-terminal region of the protein and was not previously known to be involved in modulating enzyme activity. In addition to the vacuolar inclusions, some cells in the brain of the affected cat contained inclusions that exhibited lipofuscin-like autofluorescence. Electron microscopic examinations suggested these inclusions formed via an autophagy-like process.
Topics: Cats; Animals; beta-Mannosidosis; beta-Mannosidase; Mutation, Missense
PubMed: 37913889
DOI: 10.1016/j.gene.2023.147941 -
Movement Disorders Clinical Practice Jan 2024
PubMed: 38243728
DOI: 10.1002/mdc3.13963