Reaction: Defective GLB1 does not hydrolyse a glycosaminoglycan
- in pathway: MPS IV - Morquio syndrome B
Defects in beta-galactosidase (GLB1, MIM:611458) result in galactose moieties not being hydrolysed from keratan sulfate (KS) or the GAG linker chain, a tetrasccharide sequence required for some GAG biosyntheses to take place. Mucopolysaccharidosis IV B (MPSIVB, Morquio's syndrome B; MIM:253010) is the result of GLB1 deficiency.
GLB1 mutations causing severe phenotypes are R482C (Ishii et al. 1995), W509C (Oshima et al. 1991), Y83C (Santamaria et al. 2006) and W273L Paschke et al. 2001. Mild phenotypes where a partial loss of enzyme activity occurs can involve the mutants G438E, N484K, T500A (Bagshaw et al. 2002) and Y83H (Ishii et al. 1995). These mild phenotype mutants are not detailed here.
GLB1 mutations causing severe phenotypes are R482C (Ishii et al. 1995), W509C (Oshima et al. 1991), Y83C (Santamaria et al. 2006) and W273L Paschke et al. 2001. Mild phenotypes where a partial loss of enzyme activity occurs can involve the mutants G438E, N484K, T500A (Bagshaw et al. 2002) and Y83H (Ishii et al. 1995). These mild phenotype mutants are not detailed here.
Reaction - small molecule participants:
H2O [lysosomal lumen]
Gal-GlcNAc(S)-Gal-GlcNAc(S)-Gal [lysosomal lumen]
Reactome.org reaction link: R-HSA-2265534
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Reaction input - small molecules:
water
beta-D-Galp-(1->4)-beta-D-GlcpNAc6S-(1->3)-beta-D-Galp-(1->4)-beta-D-GlcpNAc6S-(1->3)-D-Galp
Reaction output - small molecules:
Reactome.org link: R-HSA-2265534