Oligomerization and intracellular protein transport: dimerization of intestinal dipeptidylpeptidase IV occurs in the Golgi apparatus.
It was postulated that newly synthesized membrane proteins need to be assembled into oligomers in the endoplasmic reticulum in order to be transported to the Golgi apparatus. By use of the differentiated human adenocarcinoma cell line Caco-2, the general validity of this proposal was studied for small intestinal brush border enzymes which are dimers in most mammalian species. Chemical cross-linking experiments and sucrose gradient rate-zonal centrifugation revealed that dipeptidylpeptidase IV is present as a dimer in the brush border membrane of Caco-2 cells whereas the disaccharidase sucrase-isomaltase appears to be a monomer. Dipeptidylpeptidase IV was found to dimerize immediately after complex glycosylation, an event associated with the Golgi apparatus. Dimerization of this enzyme was inhibited by CCCP but did not depend on complex glycosylation of N-linked carbohydrates as assessed by the use of the trimming inhibitor 1-deoxymannojirimycin. It is concluded that dimerization of dipeptidylpeptidase IV occurs in a late Golgi compartment and therefore cannot be a prerequisite for its export from the endoplasmic reticulum.
Jascur
T
T
Department of Pharmacology, Biocenter of the University of Basel, Switzerland.
Matter
K
K
Hauri
H P
HP
D000230:Adenocarcinoma; D002460:Cell Line; D003110:Colonic Neoplasms; D003432:Cross-Linking Reagents; D018819:Dipeptidyl Peptidase 4; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D006056:Golgi Apparatus / Q000201:enzymology*; D006801:Humans; D007421:Intestine, Small / Q000201:enzymology; D046911:Macromolecular Substances; D008871:Microvilli / Q000201:enzymology; D008970:Molecular Weight; D011499:Protein Processing, Post-Translational
D003432:Cross-Linking Reagents; D046911:Macromolecular Substances; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D018819:Dipeptidyl Peptidase 4