Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.64 (proteinase K)
 4,071 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Proteases have been used as a tool to investigate the role of surface molecules in fibronectin-mediated cell adhesion. Proteolytic digestion of membrane-proteins by pronase (1 mg/ml for 20 min at 37 degrees C) completely inhibited adhesion of baby hamster kidney (BHK) fibroblasts on fibronectin-coated plastic dishes. Various degrees of inhibition were also obtained after treatment with proteinase K, chymotrypsin, papain, subtilopeptidase A, and thermolysin. Protein synthesis was required to restore the adhesive properties of pronase-treated cells, showing the protein nature of the molecules involved in adhesion to fibronectin. A peculiar feature of these proteins was their resistance to cleavage by trypsin. After prolonged trypsin treatment (1 mg/ml for 20 min at 37 degrees C), cells adhered and spread on fibronectin-coated dishes, even when protein synthesis was inhibited by 4 microM cycloheximide. Under these conditions only three glycoproteins (gp) of molecular weight 130,000, 120,000, and 80,000 were left on the cell surface. These were precipitated by a rabbit antiserum against BHK cells that also inhibited adhesion of trypsin-treated cells. gp120 and gp80 were left at the cell surface after mild pronase digestion (0.2 mg/ml for 20 min at 37 degrees C), under conditions not affecting adhesion. These data suggest that these glycoproteins may be involved in fibronectin-mediated cell adhesion in some yet unknown way.
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PMID:Cell surface molecules and fibronectin-mediated cell adhesion: effect of proteolytic digestion of membrane proteins. 674 66

The endoplasmic reticulum (ER) not only links the translational machinery to the endomembrane system in eukaryotic cells but also provides a protective environment for the folding of exoplasmic proteins translocated across the ER membrane. Here we describe that the lumenal surface of the ER membranes transiently tethers the folding intermediate of secretory proteins via a 90-kDa ER membrane protein, calnexin. We demonstrate that p70, the precursor to gp80, the major secretory protein in Madin-Darby canine kidney (MDCK) cells, was bound transiently to calnexin in the immediate post-synthetic period (0-10 min) and showed a t1/2 for dissociation from calnexin of 2.5 min. The bound p70 was found to be incompletely folded as assessed by susceptibility to proteinase K digestion. Perturbation of the redox state by 5 mM dithiothreitol or 1 mM diamide markedly inhibited the dissociation of p70 from calnexin (t1/2 > 30 min). Cellular depletion of ATP led to premature dissociation of p70 from calnexin and the formation of p70 aggregates that did not bind calnexin. These findings demonstrate that nascent unfolded p70 is tethered to calnexin during normal protein maturation, including the formation and editing of disulfide bonds and that ATP is required for the productive interaction of gp80 and calnexin.
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PMID:Chaperone function of calnexin for the folding intermediate of gp80, the major secretory protein in MDCK cells. Regulation by redox state and ATP. 790 29