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)

In contrast to other studies, our results demonstrate that low concentration of trypsin degrades a high proportion of proteolipid from CNS myelin. The Wolfgram protein and BP are vulnerable and completely lost on trypsinolysis, perhaps accounting for some of the peptides retained by the myelin. In PNS myelin, the major PO protein, a hydrophobic glycoprotein, is readily degraded to a stable 18,000--19,000 molecular weight unit, referred to as TPO protein, still retaining the carbohydrate unit which probably exists as a nonasaccharide grouping. Production of the TPO glycoprotein results from cleavage of a lysinyl-methionine or arginyl-methionine linkage probably found approximately 80--100 residues from the NH2-terminal isoleucine of the PO molecule. This linkage must be especially accessible to trypsin since the TPO protein is also generated in high yield when isolated PO protein is treated with trypsin in solution for 0.5 hours. Further incubation for 24 hours fully degrades the TPO protein to over 20 tryptic peptides, shown by peptide mapping, unlike the situation in myelin where the TPO unit is stable and resists further proteolysis. The TPO unit is also produced when PO protein is treated with BrCN. The PO protein contains 3 methionine residues but presumably the methionine residue in the trypsin-sensitive region is crucial; cleavage leads to the same TPO unit minus NH2-terminal methionine. Another methionine residue also exists in the TPO protein but it may be resistant to BrCN cleavage or else occupy a near-end position. Other proteins were also identified on PAGE of trypsinized PNS myelin: albumin, P2 protein, and PO protein. Albumin and P2 protein were identified in the acidic extract by reaction with specific antibody. The PO protein was isolated; it moved similarly to standard protein on SDS-PAGE and gave the appropriate amino acid analysis. However, it cannot be determined at this time whether a portion of these proteins remains because they are partially inaccessible to trypsin, or else are slightly attacked and thus represent early stages of trypsinolysis. The P2 protein of trypsinized myelin appears to migrate slightly faster than standard P2 protein on PAGE. Further work should clarify this point. Amino acid analysis and sequence data show that the PO protein is particularly hydrophobic, very likely existing in PNS myelin as an amphipathic molecule which penetrates the bilayer but which has a hydrophilic portion exposed. It is this hydrophilic region that contains much lysine, particularly the crucial lysinyl-methionine linkage, that is so trypsin-sensitive. Determination of the amino acid sequence of terminal portions of the isolated PO and TPO proteins serves to firmly establish the PO protein as a unique entity probably exclusive to PNS myelin. It can be concluded that the study of trypsin activity toward PNS myelin has made possible a new understanding of how proteins are positioned in the membrane, and provided valuable insight into the PO protein.
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PMID:The action of trypsin on central and peripheral nerve myelin. 69 76

When purified rabbit sciatic nerve myelin, whether lyophilized or not, is treated with low amounts of trypsin (25 microgram/ml) for 0.5, 3, or 24 h the resulting protein patterns viewed on sodium dodecyl sulfate (SDS) gel electrophoresis are similar. The most striking feature of the trypsinized myelin is the accumulation of a heavy band at the basic protein position, molecular weight 19 000, which is accounted for as a degradation product of the PO protein, referred to as the TPO protein. The PO protein, the major glycoprotein of sciatic nerve myelin, as well as the 23K and P2 proteins and albumin, an absorbed component, are all partially degraded; most high molecular weight bands are lost. The TPO protein, isolated by gel filtration in 2% SDS on an agarose column, like the PO protein, is highly insoluble in aqueous solvents. It is a glycoprotein (8% carbohydrate), staining with periodic acid-Schiff reagent; containing 3 mannose, 1 galactose, 3 N-acetylglucosamine, 1 sialic acid, and 1 fucose residues and is identical to the nonasaccharide of the parent PO protein. The amino acid composition of the TPO protein, is similar to the PO protein, but has a much higher content of hydrophobic residues and begins with NH2-methionine. This suggests that the PO protein is an amphipathic membrane protein in which its more polar character is confined to the first third of its NH2-terminus. This polar domain is probably positioned above the lipid leaflet where it is accessible to trypsin which cleaves a sensitive lysinyl (or argininyl)-methionine linkage. The more hydrophobic domain (the TPO protein) is buried in the myelin bilayer where it is protected from further tryptic attack. Thus trypsin can serve as a useful probe of myelin structure.
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PMID:Isolation of a product from the trypsin-digested glycoprotein of sciatic nerve myelin. 70 55