In vitro mutagenesis helps to unravel the biological consequences of aspartylglucosaminuria mutation.
Aspartylglucosaminuria (AGU) is a lysosomal storage disease resulting in severe mental retardation. We have recently reported that mutations in the aspartylglucosaminidase (AGA) locus are responsible for this disease. About 90% of reported AGU cases are found in Finland, and we have shown that the vast majority (98%) of AGU alleles in this isolated population contain two point mutations located 5 bp apart. We expressed these Arg161----Gln and Cys163----Ser mutations separately in vitro and demonstrated that deficient enzyme activity is caused by the Cys163----Ser mutation, whereas the Arg161----Gln substitution represents a rare polymorphism. Further analyses of in vitro expressed AGA proteins and the enzyme purified from an AGU patient revealed that Cys163 participates in and S-S bridge. The absence of this covalent cross-link in the mutated protein most probably results in disturbed folding of the polypeptide chain and a consequent decrease in its intracellular stability.
Ikonen
E
E
Laboratory of Molecular Genetics, National Public Health Institute, Helsinki, Finland.
Enomaa
N
N
Ulmanen
I
I
Peltonen
L
L
D001227:Aspartylglucosylaminase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D003001:Cloning, Molecular; D003545:Cysteine / Q000737:chemistry; D004247:DNA; D004252:DNA Mutational Analysis; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D016464:Lysosomal Storage Diseases / Q000201:enzymology / Q000235:genetics* / Q000652:urine; D008969:Molecular Sequence Data; D016296:Mutagenesis
D004220:Disulfides; D004247:DNA; D001227:Aspartylglucosylaminase; D003545:Cysteine