RESUMEN
Free oligosaccharides (fOSs) are soluble oligosaccharide species generated during N-glycosylation of proteins. Although little is known about fOS metabolism, the recent identification of NGLY1 deficiency, a congenital disorder of deglycosylation (CDDG) caused by loss of function of an enzyme involved in fOS metabolism, has elicited increased interest in fOS processing. The catabolism of fOSs has been linked to the activity of a specific cytosolic mannosidase, MAN2C1, which cleaves α1,2-, α1,3-, and α1,6-mannose residues. In this study, we report the clinical, biochemical, and molecular features of six individuals, including two fetuses, with bi-allelic pathogenic variants in MAN2C1; the individuals are from four different families. These individuals exhibit dysmorphic facial features, congenital anomalies such as tongue hamartoma, variable degrees of intellectual disability, and brain anomalies including polymicrogyria, interhemispheric cysts, hypothalamic hamartoma, callosal anomalies, and hypoplasia of brainstem and cerebellar vermis. Complementation experiments with isogenic MAN2C1-KO HAP1 cells confirm the pathogenicity of three of the identified MAN2C1 variants. We further demonstrate that MAN2C1 variants lead to accumulation and delay in the processing of fOSs in proband-derived cells. These results emphasize the involvement of MAN2C1 in human neurodevelopmental disease and the importance of fOS catabolism.
Asunto(s)
Quistes del Sistema Nervioso Central/genética , Trastornos Congénitos de Glicosilación/genética , Hamartoma/genética , Discapacidad Intelectual/genética , Oligosacáridos/metabolismo , Péptido-N4-(N-acetil-beta-glucosaminil) Asparagina Amidasa/deficiencia , Polimicrogiria/genética , alfa-Manosidasa/genética , Adolescente , Alelos , Tronco Encefálico/metabolismo , Tronco Encefálico/patología , Línea Celular Tumoral , Quistes del Sistema Nervioso Central/metabolismo , Quistes del Sistema Nervioso Central/patología , Vermis Cerebeloso/metabolismo , Vermis Cerebeloso/patología , Niño , Preescolar , Trastornos Congénitos de Glicosilación/metabolismo , Trastornos Congénitos de Glicosilación/patología , Femenino , Feto , Glicosilación , Hamartoma/metabolismo , Hamartoma/patología , Humanos , Hipotálamo/metabolismo , Hipotálamo/patología , Discapacidad Intelectual/metabolismo , Discapacidad Intelectual/patología , Leucocitos/metabolismo , Leucocitos/patología , Masculino , Manosa/metabolismo , Péptido-N4-(N-acetil-beta-glucosaminil) Asparagina Amidasa/genética , Péptido-N4-(N-acetil-beta-glucosaminil) Asparagina Amidasa/metabolismo , Polimicrogiria/metabolismo , Polimicrogiria/patología , Lengua/metabolismo , Lengua/patología , alfa-Manosidasa/deficienciaRESUMEN
Acidic peptide:N-glycanase (aPNGase) plays a pivotal role in plant glycoprotein turnover. For the construction of aPNGase-knockout or -overexpressing plants, a new method to detect the activity in crude plant extracts is required because endogenous peptidases present in the extract hamper enzyme assays using fluorescence-labeled N-glycopeptides as a substrate. In this study, we developed a new method for measuring aPNGase activity in crude extracts from plant materials.