Cloning and primary structure of a human islet isoform of glutamic acid decarboxylase from chromosome 10.
Glutamic acid decarboxylase (GAD; glutamate decarboxylase, L-glutamate 1-carboxy-lyase, EC 4.1.1.15), which catalyzes formation of gamma-aminobutyric acid from L-glutamic acid, is detectable in different isoforms with distinct electrophoretic and kinetic characteristics. GAD has also been implicated as an autoantigen in the vastly differing autoimmune disease stiff-man syndrome and insulin-dependent diabetes mellitus. Despite the differing GAD isoforms, only one type of GAD cDNA (GAD-1), localized to a syntenic region of chromosome 2, has been isolated from rat, mouse, and cat. Using sequence information from GAD-1 to screen a human pancreatic islet cDNA library, we describe the isolation of an additional GAD cDNA (GAD-2), which was mapped to the short arm of human chromosome 10. Genomic Southern blotting with GAD-2 demonstrated a hybridization pattern different from that detected by GAD-1. GAD-2 recognizes a 5.6-kilobase transcript in both islets and brain, in contrast to GAD-1, which detects a 3.7-kilobase transcript in brain only. The deduced 585-amino acid sequence coded for by GAD-2 shows less than 65% identity to previously published, highly conserved GAD-1 brain sequences, which show greater than 96% deduced amino acid sequence homology among the three species. The function of this additional islet GAD isoform and its importance as an autoantigen in insulin-dependent diabetes remain to be determined.
Karlsen
A E
AE
Department of Medicine, University of Washington, Seattle 98195.
Hagopian
W A
WA
Grubin
C E
CE
Dube
S
S
Disteche
C M
CM
Adler
D A
DA
Bärmeier
H
H
Mathewes
S
S
Grant
F J
FJ
Foster
D
D
Lernmark
Åke
Å
D000595:Amino Acid Sequence; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D002874:Chromosome Mapping; D002879:Chromosomes, Human, Pair 10; D003001:Cloning, Molecular; D015870:Gene Expression; D005796:Genes; D005969:Glutamate Dehydrogenase / Q000235:genetics*; D006801:Humans; D007515:Islets of Langerhans / Q000201:enzymology*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012333:RNA, Messenger / Q000235:genetics; D016415:Sequence Alignment
D012333:RNA, Messenger; D005969:Glutamate Dehydrogenase