Molecular consequences of the pathogenic mutation in feline GM1 gangliosidosis.
G(M1) gangliosidosis is an inherited, fatal neurodegenerative disease caused by deficiency of lysosomal beta-d-galactosidase (EC 3.2.1.23) and consequent storage of undegraded G(M1) ganglioside. To characterize the genetic mutation responsible for feline G(M1) gangliosidosis, the normal sequence of feline beta-galactosidase cDNA first was defined. The feline beta-galactosidase open reading frame is 2010 base pairs, producing a protein of 669 amino acids. The putative signal sequence consists of amino acids 1-24 of the beta-galactosidase precursor protein, which contains seven potential N-linked glycosylation sites, as in the human protein. Overall sequence homology between feline and human beta-galactosidase is 74% for the open reading frame and 82% for the amino acid sequence. After normal beta-galactosidase was sequenced, the mutation responsible for feline G(M1) gangliosidosis was defined as a G to C substitution at position 1448 of the open reading frame, resulting in an amino acid substitution at arginine 483, known to cause G(M1) gangliosidosis in humans. Feline beta-galactosidase messenger RNA levels were normal in cerebral cortex, as determined by quantitative RT-PCR assays. Although enzymatic activity is severely reduced by the mutation, a full-length feline beta-galactosidase cDNA restored activity in transfected G(M1) fibroblasts to 18-times normal. beta-Galactosidase protein levels in G(M1) tissues were normal on Western blots, but immunofluorescence analysis demonstrated that the majority of mutant beta-galactosidase protein did not reach the lysosome. Additionally, G(M1) cat fibroblasts demonstrated increased expression of glucose-related protein 78/BiP and protein disulfide isomerase, suggesting that the unfolded protein response plays a role in pathogenesis of feline G(M1) gangliosidosis.
Martin
Douglas R
DR
Scott-Ritchey Research Center, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, USA. martidr@auburn.edu
Rigat
Brigitte A
BA
Foureman
Polly
P
Varadarajan
G S
GS
Hwang
Misako
M
Krum
Barbara K
BK
Smith
Bruce F
BF
Callahan
John W
JW
Mahuran
Don J
DJ
Baker
Henry J
HJ
D019943:Amino Acid Substitution; D000818:Animals; D002371:Cat Diseases / Q000201:enzymology / Q000235:genetics*; D002415:Cats; D002460:Cell Line; D002478:Cells, Cultured; D003001:Cloning, Molecular; D000091342:Endoplasmic Reticulum Chaperone BiP; D005347:Fibroblasts / Q000201:enzymology; D016537:Gangliosidosis, GM1 / Q000201:enzymology / Q000235:genetics* / Q000662:veterinary*; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D018832:Molecular Chaperones / Q000378:metabolism; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D016366:Open Reading Frames; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D021381:Protein Transport; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics* / Q000378:metabolism
D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D001616:beta-Galactosidase; D019704:Protein Disulfide-Isomerases