Human Islet Glucokinase Gene. Isolation and Sequence. Analysis of Full-Length cDNA. LASZLO I. KORANYI, YUKIO TANIZAWA, CRIS M. WELLING, DANIEL U.
Human Islet Glucokinase Gene Isolation and Sequence Analysis of Full-Length cDNA LASZLO I. KORANYI, YUKIO TANIZAWA, CRIS M. WELLING, DANIEL U. RABIN, AND M. ALAN PERMUTT
Pancreatic islet glucokinase (ATP:D-hexose-6-phosphotransferase) cDNAs were isolated from a human islet cDNA library in X-gt11. One clone (hIGLKZ), 2723 bp plus additional poly(A) residues, appeared to be full length because its size was consistent with a single 2.9-kb glucokinase mRNA on Northern-blot analysis of islet RNA. This cDNA contained an open reading frame of 1395 bp from an ATG codon at position 459, encoding a predicted protein of 465 amino acids (52,000 Mr). Comparison of the nucleotide sequences of the human islet glucokinase cDNA with that of the recently isolated human liver glucokinase cDNA revealed that the two cDNAs differed completely on their 5'-ends, followed by an identical 2204-bp overlap extending to the 3'-ends. The 5'-ends of islet and liver glucokinase cDNAs predicted proteins that differ by 15 NH2-terminal residues. The overall sequence identity (70%) between the first exons of the human islet and rat islet cDNAs suggested that the islet promoter regions, like the liver promoter regions, have been conserved through evolution. Thus, NH2-terminal differences for human liver and islet enzymes might be explained by use of alternate promoters between the two tissues, analogous to the NH2-terminal differences of the rat liver and rat islet enzymes. If so, this relationship predicts important tissue-specific regulatory functions of these regions. Variations in the glucokinase gene are likely to occur in humans. Isolation of a human islet glucokinase cDNA has provided the sequence necessary to determine whether these variants are important determinants in the genetic predisposition for diabetes mellitus. Diabetes 41:807-11,1992
From the Metabolism Division, Washington University School of Medicine, St. Louis, Missouri; and Molecular Diagnostics, Miles Research Center, West Haven, Connecticut. Address correspondence and reprint requests to M. Alan Permutt, MD, Metabolism Division, Washington University School of Medicine, 660 South Euclid Avenue, Box 8127, St. Louis, MO 63110. The sequence reported in this article has been deposited in the Gene Bank data base (accession no. M90299). Received for publication 9 August 1991 and accepted in revised form 3 March 1992.
DIABETES, VOL. 41, JULY 1992
G
lucokinase (ATP:D-hexose-6-phosphotransferase), one member (hexokinase IV) of a family of hexokinases, is the major glucose phosphorylating enzyme of liver and pancreatic islet (3-cells (1-4). Glucokinase is distinguished from the other hexokinases by its lack of inhibition by glucose-6phosphate and by its Km in the physiological range of plasma glucose concentration (5-15 mM), such that glucose phosphorylation maintains a gradient for glucose transport into liver and islet p-cells. Glucose metabolism in islet (3-cells, an important determinant of insulin synthesis and secretion, is directly proportional to plasma glucose concentrations (5,6). The presence of a high-/
