Description: Homo sapiens hexosaminidase B (beta polypeptide) (HEXB), mRNA. RefSeq Summary (NM_000521): Hexosaminidase B is the beta subunit of the lysosomal enzyme beta-hexosaminidase that, together with the cofactor GM2 activator protein, catalyzes the degradation of the ganglioside GM2, and other molecules containing terminal N-acetyl hexosamines. Beta-hexosaminidase is composed of two subunits, alpha and beta, which are encoded by separate genes. Both beta-hexosaminidase alpha and beta subunits are members of family 20 of glycosyl hydrolases. Mutations in the alpha or beta subunit genes lead to an accumulation of GM2 ganglioside in neurons and neurodegenerative disorders termed the GM2 gangliosidoses. Beta subunit gene mutations lead to Sandhoff disease (GM2-gangliosidosis type II). Alternatively spliced transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, May 2014]. Transcript (Including UTRs) Position: hg19 chr5:73,980,969-74,017,113 Size: 36,145 Total Exon Count: 14 Strand: + Coding Region Position: hg19 chr5:73,981,086-74,017,000 Size: 35,915 Coding Exon Count: 14
ID:HEXB_HUMAN DESCRIPTION: RecName: Full=Beta-hexosaminidase subunit beta; EC=3.2.1.52; AltName: Full=Beta-N-acetylhexosaminidase subunit beta; Short=Hexosaminidase subunit B; AltName: Full=Cervical cancer proto-oncogene 7 protein; Short=HCC-7; AltName: Full=N-acetyl-beta-glucosaminidase subunit beta; Contains: RecName: Full=Beta-hexosaminidase subunit beta chain B; Contains: RecName: Full=Beta-hexosaminidase subunit beta chain A; Flags: Precursor; FUNCTION: Responsible for the degradation of GM2 gangliosides, and a variety of other molecules containing terminal N-acetyl hexosamines, in the brain and other tissues. CATALYTIC ACTIVITY: Hydrolysis of terminal non-reducing N-acetyl- D-hexosamine residues in N-acetyl-beta-D-hexosaminides. SUBUNIT: There are 3 forms of beta-hexosaminidase: hexosaminidase A is a trimer composed of one subunit alpha, one subunit beta chain A and one subunit beta chain B; hexosaminidase B is a tetramer of two subunit beta chains A and two subunit beta chains B; hexosaminidase S is a homodimer of two alpha subunits. The two beta chains are derived from the cleavage of the beta subunit. SUBCELLULAR LOCATION: Lysosome. PTM: N-linked glycans at Asn-142 and Asn-190 consist of Man(3)- GlcNAc(2) and Man(5 to 7)-GlcNAc(2), respectively. PTM: The beta-A and beta-B chains are produced by proteolytic processing of the precursor beta chain. DISEASE: Defects in HEXB are the cause of GM2-gangliosidosis type 2 (GM2G2) [MIM:268800]; also known as Sandhoff disease. GM2- gangliosidosis is an autosomal recessive lysosomal storage disease marked by the accumulation of GM2 gangliosides in the neuronal cells. GM2G2 is clinically indistinguishable from GM2- gangliosidosis type 1, presenting startle reactions, early blindness, progressive motor and mental deterioration, macrocephaly and cherry-red spots on the macula. SIMILARITY: Belongs to the glycosyl hydrolase 20 family. SEQUENCE CAUTION: Sequence=AAA51828.1; Type=Frameshift; Positions=21; Sequence=AAA68620.1; Type=Erroneous initiation; WEB RESOURCE: Name=HEXBdb; Note=HEXB mutation database; URL="http://www.hexdb.mcgill.ca/?Topic=HEXBdb"; WEB RESOURCE: Name=GeneReviews; URL="http://www.ncbi.nlm.nih.gov/sites/GeneTests/lab/gene/HEXB";
dramatically different phenotypes McInnes B et al. 1992, An unusual splicing mutation in the HEXB gene is associated with dramatically different phenotypes in patients from different racial backgrounds., The Journal of clinical investigation. 1992 Aug;90(2):306-14.
[PubMed 1386607]
The RNAfold program from the Vienna RNA Package is used to perform the secondary structure predictions and folding calculations. The estimated folding energy is in kcal/mol. The more negative the energy, the more secondary structure the RNA is likely to have.
ModBase Predicted Comparative 3D Structure on P07686
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Orthologous Genes in Other Species
Orthologies between human, mouse, and rat are computed by taking the best BLASTP hit, and filtering out non-syntenic hits. For more distant species reciprocal-best BLASTP hits are used. Note that the absence of an ortholog in the table below may reflect incomplete annotations in the other species rather than a true absence of the orthologous gene.
Gene Ontology (GO) Annotations with Structured Vocabulary
Molecular Function: GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds GO:0004563 beta-N-acetylhexosaminidase activity GO:0005515 protein binding GO:0008375 acetylglucosaminyltransferase activity GO:0016787 hydrolase activity GO:0016798 hydrolase activity, acting on glycosyl bonds GO:0042803 protein homodimerization activity GO:0046982 protein heterodimerization activity
Biological Process: GO:0001501 skeletal system development GO:0005975 carbohydrate metabolic process GO:0006687 glycosphingolipid metabolic process GO:0006689 ganglioside catabolic process GO:0006874 cellular calcium ion homeostasis GO:0007040 lysosome organization GO:0007338 single fertilization GO:0007341 penetration of zona pellucida GO:0007605 sensory perception of sound GO:0007626 locomotory behavior GO:0008049 male courtship behavior GO:0008152 metabolic process GO:0008360 regulation of cell shape GO:0008654 phospholipid biosynthetic process GO:0009313 oligosaccharide catabolic process GO:0019915 lipid storage GO:0019953 sexual reproduction GO:0030203 glycosaminoglycan metabolic process GO:0030207 chondroitin sulfate catabolic process GO:0030214 hyaluronan catabolic process GO:0031323 regulation of cellular metabolic process GO:0042340 keratan sulfate catabolic process GO:0042552 myelination GO:0043312 neutrophil degranulation GO:0043615 astrocyte cell migration GO:0044267 cellular protein metabolic process GO:0045944 positive regulation of transcription from RNA polymerase II promoter GO:0048477 oogenesis GO:0050885 neuromuscular process controlling balance GO:0050905 neuromuscular process