Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glucosidase I, the first enzyme in the N-linked oligosaccharide processing pathway, cleaves the distal alpha 1,2-linked glucose residue from the Glc3-Man9-GlcNAc2 oligosaccharide precursor highly specifically. A human hippocampus cDNA library was screened against oligonucleotide probes, generated by PCR using primers derived from the amino acid sequences of tryptic peptides of pig liver glucosidase I. Two independent lambda clones were isolated which allowed the construction of a full-length glucosidase I cDNA of 2881 bp. This cDNA construct encodes, in a single open reading frame, a polypeptide of 834 amino acids corresponding to a molecular mass of 92 kDa. The 92-kDa protein contains a single N-glycosylation site of the Asn-Xaa-Thr/Ser type at Asn655, as well as a strongly hydrophobic sequence close to its N-terminus (amino acids 38-58) which, most likely, functions as a transmembrane anchor. The amino acid sequences of all tryptic peptides of the pig liver enzyme were found, with little deviation, within the coding sequence. This demonstrates the authenticity of the cDNA construct and the close evolutionary relationship between the enzymes from human hippocampus and pig liver. In contrast, the nucleotide and amino acid sequence revealed no homology with other processing enzymes cloned so far. Transfection of COS 1 cells with the glucosidase I cDNA construct resulted in overexpression (about fourfold) of enzymic activity, which was inhibited strongly by 1-deoxynojirimycin or N,N-dimethyl-deoxynojirimycin. The expressed enzyme, with a molecular mass of 95 kDa, is degraded by endoglycosidase H to a 93-kDa form, indicating that it carries a high-mannose oligosaccharide chain at Asn655. The presence of this glycan is in line with the localization of glucosidase I in the lumen of the endoplasmic reticulum, shown by immunofluorescence microscopy. The hydrophobicity profile as well as the removal by trypsin of an approximately 4-kDa polypeptide from the membrane-associated glucosidase I in intact microsomal structures, supports the view that the enzyme is a type-II transmembrane glycoprotein, which contains a short cytosolic tail of approximately 37 amino acids, followed by a single transmembrane domain and a large C-terminal catalytic domain located on the luminal side of the endoplasmic reticulum membrane.
 ...
PMID:Cloning and expression of glucosidase I from human hippocampus. 763 46

Glucosidase I initiates the processing of the oligosaccharide, Glc3Man9GlcNAc2, in newly assembled glycoproteins by excising the distal alpha 1,2-linked glucosyl residue in the oligosaccharide. Earlier, the enzyme purified from the ER of rat and bovine mammary gland has been found to have M(r) of 85 kDa, as examined by SDS-PAGE along with a domain structure in which a 39 kDa lumenally-oriented region is anchored to the ER through a transmembrane segment and a short cytoplasmic tail. These studies were further extended to include the enzyme from several different tissues of the rat, mouse, guinea pig and bovine mammary glands, sheep liver and pig kidney. Using anti-rat glucosidase I antibody as a probe and several biochemical parameters such as SDS-PAGE analysis, trypsin-catalyzed digestion, ConA-binding, endo H susceptibility and peptide mapping analysis by cleavage of the tryptophanyl peptide linkages within the enzyme, it was found that glucosidase I in all of the tissue sources examined has an M(r) of 85 kDa and is cross-reactive to anti-rat glucosidase antibody. The enzyme is a high mannose glycoprotein, and has domain features in its structure; the enzyme from mouse, rat, guinea pig and bovine mammary glands and sheep liver is sequentially cleaved by trypsin to generate fragments of 69, 55 and 39 kDa. The rate of release of the different fragments differs for different sources, indicating some evolutionary changes in its primary structure. The trypsin-released fragments from pig kidney enzyme are 69, 45 and 29 kDa in size, identical to the same observed earlier for pig liver.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Conserved structural features in glycoprotein processing glucosidase I from several tissues and species. 800 15