CRYSTAL STRUCTURE OF AN ARYLSULFATASE A MUTANT C69S
[ARSA_HUMAN] Defects in ARSA are a cause of leukodystrophy metachromatic (MLD) [MIM:250100]. MLD is a disease due to a lysosomal storage defect. It is characterized by intralysosomal storage of cerebroside-3-sulfate in neural and non-neural tissues, with a diffuse loss of myelin in the central nervous system. Progressive demyelination causes a variety of neurological symptoms, including gait disturbances, ataxias, optical atrophy, dementia, seizures, and spastic tetraparesis. Three forms of the disease can be distinguished according to the age at onset: late-infantile, juvenile and adult.                                         Arylsulfatase A activity is defective in multiple sulfatase deficiency (MSD) [MIM:272200]. A clinically and biochemically heterogeneous disorder caused by the simultaneous impairment of all sulfatases, due to defective post-translational modification and activation. It combines features of individual sulfatase deficiencies such as metachromatic leukodystrophy, mucopolysaccharidosis, chondrodysplasia punctata, hydrocephalus, ichthyosis, neurologic deterioration and developmental delay. Note=Arylsulfatase A activity is impaired in multiple sulfatase deficiency due to mutations in SUMF1. SUMF1 mutations result in defective post-translational modification of ARSA at residue Cys-69 that is not converted to 3-oxoalanine. 
[ARSA_HUMAN] Hydrolyzes cerebroside sulfate.
Publication Abstract from PubMed
Arylsulfatase A (ASA) belongs to the sulfatase family whose members carry a C(alpha)-formylglycine that is post-translationally generated by oxidation of a conserved cysteine or serine residue. The crystal structures of two arylsulfatases, ASA and ASB, and kinetic studies on ASA mutants led to different proposals for the catalytic mechanism in the hydrolysis of sulfate esters.The structures of two ASA mutants that lack the functional C(alpha)-formylglycine residue 69, in complex with a synthetic substrate, have been determined in order to unravel the reaction mechanism. The crystal structure of the inactive mutant C69A-ASA in complex with p-nitrocatechol sulfate (pNCS) mimics a reaction intermediate during sulfate ester hydrolysis by the active enzyme, without the covalent bond to the key side-chain FGly69. The structure shows that the side-chains of lysine 123, lysine 302, serine 150, histidine 229, the main-chain of the key residue 69 and the divalent cation in the active center are involved in sulfate binding. It is proposed that histidine 229 protonates the leaving alcoholate after hydrolysis.C69S-ASA is able to bind covalently to the substrate and hydrolyze it, but is unable to release the resulting sulfate. Nevertheless, the resulting sulfation is low. The structure of C69S-ASA shows the serine side-chain in a single conformation, turned away from the position a substrate occupies in the complex. This suggests that the double conformation observed in the structure of wild-type ASA is more likely to correspond to a formylglycine hydrate than to a twofold disordered aldehyde oxo group, and accounts for the relative inertness of the C69S-ASA mutant. In the C69S-ASA-pNCS complex, the substrate occupies the same position as in the C69A-ASA-pNCS complex, which corresponds to the non-covalently bonded substrate. Based on the structural data, a detailed mechanism for sulfate ester cleavage is proposed, involving an aldehyde hydrate as the functional group.
Crystal structure of an enzyme-substrate complex provides insight into the interaction between human arylsulfatase A and its substrates during catalysis.,von Bulow R, Schmidt B, Dierks T, von Figura K, Uson I J Mol Biol. 2001 Jan 12;305(2):269-77. PMID:11124905
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.