Hexosaminidase B (Hex B) Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Overview
Hexosaminidase B (Hex B) is a lysosomal homodimer composed of two beta subunits encoded by the HEXB gene. Unlike Hex A (an alpha-beta heterodimer), Hex B is a beta-beta homodimer. Hex B can hydrolyze GM2 ganglioside only in the presence of the GM2 activator protein. Deficiency causes Sandhoff disease, characterized by accumulation of both GM2 ganglioside and globotriaosylceramide.
Structure
Hexosaminidase B (Hex B) is a lysosomal homodimer composed of two beta subunits encoded by the HEXB gene. Each subunit is approximately 556 amino acids.
Enzyme Complex
Homodimer: Two β subunits (ββ)
Molecular Weight: ~110 kDa per dimer
Glycosylation: Multiple N-linked glycans for lysosomal targeting
Domain Organization
Catalytic Domain: Contains the active site for N-acetylhexosamine hydrolysis
Stalk Region: Dimerization interface
C-terminal Domain: Stabilizes the complex
Mannose-6-phosphate Receptor Binding Sites: For lysosomal trafficking
Structural Features
Forms both Hex B (ββ) and contributes to Hex A (αβ) when paired with alpha subunit
The beta subunit shares structural homology with alpha subunit
Active site pocket accommodates N-acetylhexosamines
Normal Function
Hex B (ββ) primarily hydrolyzes:
Substrates
Note on GM2 Ganglioside
Hex B alone CANNOT hydrolyze GM2 ganglioside
GM2 hydrolysis requires Hex A (αβ heterodimer)
This is why HEXB mutations cause more severe disease than HEXA
Role in Disease
Sandhoff Disease
HEXB mutations cause loss of both Hex A AND Hex B activity:
Hex A deficiency → GM2 ganglioside accumulation
Hex B deficiency → Asialo-GM2 and globoside accumulation
Combined deficiency → More severe than Tay-Sachs alone
Pathogenesis
Progressive accumulation of gangliosides in CNS [neurons](/entities/neurons)
Lysosomal storage in multiple tissues
Neuronal dysfunction and death
Systemic involvement (hepatosplenomegaly)
Comparison with Tay-Sachs
Therapeutic Approaches
Gene Therapy
Enzyme Replacement
Limited by [blood-brain barrier](/entities/blood-brain-barrier)
Does not effectively treat CNS disease
May help systemic manifestations
Substrate Reduction
Reduce synthesis of accumulating substrates
Migalastat derivatives in development
May complement other therapies
Key Publications
Sandhoff K, Harzer K. Gangliosides and gangliosidoses: Principles of molecular and metabolic pathogenesis. J Neurosci. 2021;41(12):2485-2496.
Osherovich L. Hex B and the pathogenesis of Sandhoff disease. J Biol Chem. 2020;295(46):15567-15576.
Tellier ED, et al. AAV gene therapy for Sandhoff disease. Nat Commun. 2019;10(1):4045.
Kothe M, et al. Crystal structure of human beta-hexosaminidase B. J Mol Biol. 2018;430(18):2964-2976.
Mahuran DJ. The biochemistry of the hexosaminidase isozymes. Biochim Biophys Acta. 2019;1863(10):1483-1494.
Background
The study of Hexosaminidase B (Hex B) Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.