In Cellulo Examination of a Beta-Alpha Hybrid Construct of Beta-Hexosaminidase A Subunits, Reported to Interact with the GM2 Activator Protein and Hydrolyze GM2 Ganglioside

The hydrolysis in lysosomes of GM2 ganglioside to GM3 ganglioside requires the correct synthesis, intracellular assembly and transport of three separate gene products; i.e., the alpha and beta subunits of heterodimeric beta-hexosaminidase A, E.C. # 3.2.1.52 (encoded by the HEXA and HEXB genes, respectively), and the GM2-activator protein (GM2AP, encoded by the GM2A gene). Mutations in any one of these genes can result in one of three neurodegenerative diseases collectively known as GM2 gangliosidosis (HEXA, Tay-Sachs disease, MIM # 272800; HEXB, Sandhoff disease, MIM # 268800; and GM2A, AB-variant form, MIM # 272750). Elements of both of the hexosaminidase A subunits are needed to productively interact with the GM2 ganglioside-GM2AP complex in the lysosome. Some of these elements have been predicted from the crystal structures of hexosaminidase and the activator. Recently a hybrid of the two subunits has been constructed and reported to be capable of forming homodimers that can perform this reaction in vivo, which could greatly simplify vector-mediated gene transfer approaches for Tay-Sachs or Sandhoff diseases. A cDNA encoding a hybrid hexosaminidase subunit capable of dimerizing and hydrolyzing GM2 ganglioside could be incorporated into a single vector, whereas packaging both subunits of hexosaminidase A into vectors, such as adeno-associated virus, would be impractical due to size constraints. In this report we examine the previously published hybrid construct (H1) and a new more extensive hybrid (H2), with our documented in cellulo (live cell- based) assay utilizing a fluorescent GM2 ganglioside derivative. Unfortunately when Tay-Sachs cells were transfected with either the H1 or H2 hybrid construct and then were fed the GM2 derivative, no significant increase in its turnover was detected. In vitro assays with the isolated H1 or H2 homodimers confirmed that neither was capable of human GM2AP-dependent hydrolysis of GM2 ganglioside.

In Cellulo Examination of a Beta-Alpha Hybrid Construct of Beta-Hexosaminidase A Subunits, Reported to Interact with the GM2 Activator Protein and Hydrolyze GM2 Ganglioside

The hydrolysis in lysosomes of GM2 ganglioside to GM3 ganglioside requires the correct synthesis, intracellular assembly and transport of three separate gene products; i.e., the alpha and beta subunits of heterodimeric beta-hexosaminidase A, E.C. # 3.2.1.52 (encoded by the HEXA and HEXB genes, respectively), and the GM2-activator protein (GM2AP, encoded by the GM2A gene). Mutations in any one of these genes can result in one of three neurodegenerative diseases collectively known as GM2 gangliosidosis (HEXA, Tay-Sachs disease, MIM # 272800; HEXB, Sandhoff disease, MIM # 268800; and GM2A, AB-variant form, MIM # 272750). Elements of both of the hexosaminidase A subunits are needed to productively interact with the GM2 ganglioside-GM2AP complex in the lysosome. Some of these elements have been predicted from the crystal structures of hexosaminidase and the activator. Recently a hybrid of the two subunits has been constructed and reported to be capable of forming homodimers that can perform this reaction in vivo, which could greatly simplify vector-mediated gene transfer approaches for Tay-Sachs or Sandhoff diseases. A cDNA encoding a hybrid hexosaminidase subunit capable of dimerizing and hydrolyzing GM2 ganglioside could be incorporated into a single vector, whereas packaging both subunits of hexosaminidase A into vectors, such as adeno-associated virus, would be impractical due to size constraints. In this report we examine the previously published hybrid construct (H1) and a new more extensive hybrid (H2), with our documented in cellulo (live cell- based) assay utilizing a fluorescent GM2 ganglioside derivative. Unfortunately when Tay-Sachs cells were transfected with either the H1 or H2 hybrid construct and then were fed the GM2 derivative, no significant increase in its turnover was detected. In vitro assays with the isolated H1 or H2 homodimers confirmed that neither was capable of human GM2AP-dependent hydrolysis of GM2 ganglioside.

Two patients from Turkey with a novel variant in the GM2A gene and review of the literature

Objectives GM2 gangliosidosis is a rare form of inborn errors of metabolism including Tay-Sachs disease, Sandhoff disease, and GM2 activator deficiency. GM2 activator protein deficiency is an ultra-rare form of GM2 gangliosidosis. To date, 16 cases of GM2 activator protein deficiency have been reported in the literature, and among them, 11 cases were the infantile form of the disease. Here we report the first two patients from Turkey with the infantile form of the disease with a novel likely pathogenic variant. Case presentation A boy of eight months old presented to the metabolic department with very mild neurological deterioration, although he had achieved early developmental milestones at the appropriate time. The parents also had a daughter who had lost skills progressively before one year of age. The boy was evaluated and bilateral cherry-red spots were found with no abnormality in either metabolic screening including β-hexosaminidase or cranial magnetic resonance imaging. A novel homozygous likely pathogenic variant in GM2A was detected in a next-generation sequence panel revealing GM2 activator protein deficiency. His sister was investigated after he was diagnosed with GM2 activator deficiency and it was found that she had the same variant as her brother. Conclusions This case report emphasizes that in the event of normal β-hexosaminidase activity, GM2 activator protein deficiency could be underdiagnosed, and further molecular analysis should be performed. To the best of our knowledge, this boy is one of the youngest patient diagnosed with very mild symptoms. With this novel pathogenic variant, these patients have expanded the mutation spectrum of GM2 activator protein deficiency.

A label-free immunosensor for the detection of a new lung cancer biomarker, GM2 activator protein, using a phosphomolybdic acid/polyethyleneimine coated gold nanoparticle composite

A novel electrochemical immunosensor for the detection of a new lung cancer biomarker based on a polyoxometalate-adsorbed poly(ethylenimine)-coated gold nanoparticle modified electrode.

229 Discovery of ganglioside GM2 activator as a novel proteomic biomarker associated with response to treatment in first-line melanoma subjects treated with PD-1 immunotherapy

BackgroundImmune checkpoint inhibitors (ICI) have greatly improved the treatment options for patients with metastatic melanoma. Yet, a large percentage of melanoma patients do not respond to ICIs, there is a need for biomarkers that can predict patients‘ clinical benefit thereby identifying the patient population most likely to respond. Here, we apply unbiased discovery proteomics to deeply characterize global tumor proteomes and associate proteins and pathways at baseline with clinical response to anti-PD-1 immunotherapy.MethodsUnbiased, data-independent acquisition (DIA) mass spectrometry was used to analyze Formalin Fixed Paraffin Embedded (FFPE) tumor tissue from subjects with stage IIIc-IV melanoma which were resected prior to initiation of first-line anti-PD-1 therapy. The selected samples represent two distinct clinical subgroups; those who received clinical benefit (CR or PR by RECIST criteria or OS >1 year with SD by RECIST criteria, n = 13), and those with no clinical benefit (PD by RECIST criteria or OS <1 year with SD by RECIST criteria n = 9). Previously, the sample cohort had been analyzed by a 2-hour LC-MS/MS gradient setup operated in DIA mode. In this study, all samples were analysed with a longer gradient of 4-hours which enabled the quantification of 1’000 more proteins and enabled an updated analysis with a deeper level of characterization.Results8’548 proteins were quantified across all samples, with 7’416 quantified on average per sample. Univariate statistical testing between groups identified 285 proteins that were significantly regulated in subjects who received clinical benefit. Through partial least squares discriminant analysis (PLS-DA) a set of 25 proteins was identified that describe the variance between the two sample groups. Ganglioside GM2 activator (GM2A) and other members of its interaction network such as HEXB, HRNR and CPPED1 were identified to be upregulated in the non-responder group.ConclusionsGlobal profiling of the baseline tumor proteome provides a unique characterization of melanoma tumor biology. A signature of 25 protein markers was identified as a driver of separation between responder and non-responder patients to PD-1 blockade. Among the protein markers, GM2A and its interactors, were previously shown to perturb T cell function, which might explain their enrichment in the non-responder group and provide an attractive target for improving patient response to immunotherapy.

Insilico Analysis Reveal Three novel nsSNPs May effect on GM2A protein Leading to AB variant of GM2 gangliosidosis

ABSTRACTBackgroundAB variant of GM2 gangliosidosis caused as a result of mutations in GM2 activator gene (GM2A) which is regarded as neurodegenerative disorder. This study aimed to predict the possible damaging SNPs of this gene and their impact on the protein using different bioinformatics tools.MethodsSNPs retrieved from the NCBI database were analyzed using several bioinformatics tools. The different tools collectively predicted the effect of single nucleotide substitution on both structure and function of GM2 activator.ResultsThree novel mutations were found to be highly damaging to the structure and function of the GM2A gene.ConclusionFour SNPs were found to be highly damaging SNPs that affect function, structure and stability of GM2A protein, which they are: C99Y, C112F, C138S and C138R, three of them are novel SNPs (C99Y, C112F and C138S). Also 46 SNPs were predicted to affect miRNAs binding sites on 3’UTR leading to abnormal expression of the resulting protein. These SNPs should be considered as important candidates in causing AB variant of GM2 gangliosidosis and may help in diagnosis and genetic screening of the disease.

Membrane lipids and their degradation compounds control GM2 catabolism at intralysosomal luminal vesicles

The catabolism of ganglioside GM2 is dependent on three gene products. Mutations in any of these genes result in a different type of GM2 gangliosidosis (Tay-Sachs disease, Sandhoff disease, and the B1 and AB variants of GM2 gangliosidosis), with GM2 as the major lysosomal storage compound. GM2 is also a secondary storage compound in lysosomal storage diseases such as Niemann-Pick disease types A–C, with primary storage of SM in type A and cholesterol in types B and C, respectively. The reconstitution of GM2 catabolism at liposomal surfaces carrying GM2 revealed that incorporating lipids into the GM2-carrying membrane such as cholesterol, SM, sphingosine, and sphinganine inhibits GM2 hydrolysis by β-hexosaminidase A assisted by GM2 activator protein, while anionic lipids, ceramide, fatty acids, lysophosphatidylcholine, and diacylglycerol stimulate GM2 catabolism. In contrast, the hydrolysis of the synthetic, water-soluble substrate 4-methylumbelliferyl-6-sulfo-2-acetamido-2-deoxy-β-d-glucopyranoside was neither significantly affected by membrane lipids such as ceramide or SM nor stimulated by anionic lipids such as bis(monoacylglycero)phosphate added as liposomes, detergent micelles, or lipid aggregates. Moreover, hydrolysis-inhibiting lipids also had an inhibiting effect on the solubilization and mobilization of membrane-bound lipids by the GM2 activator protein, while the stimulating lipids enhanced lipid mobilization.—