Polypeptide degradation

Two recently isolated serine proteases have quite different specificities. One is a protease of Staphylococcus aureus which has a high specificity for glutamic acid residues at Pi 16, 17). The other is the yeast carboxypeptidase listed in Table I 11), As the name indicates, it degrades polypeptides by cleaving amino acid residues from the C-terminal end of the chain—a most unexpected specificity for a serine protease. Unlike Carboxypeptidase A, it is stable, is capable of removing proline residues, and would seem to be an ideal enzyme for determining C-terminal sequences. 

The principles of fluorescence quenching have been successfully applied to assays for protease activity. Proteases are digestive enzymes that degrade polypeptides into smaller oligopeptides or constituent amino acids. A general assay12 for protease activity employs a substrate prepared by covalently derivatizing a protein, transferrin, with a number of fluorescein isothiocyanate (FITC) labels. The FITC labeled proteins (Fig. 3.3) exhibit absorbance maxima at 495 nm and emission maxima at 525 nm. 

As the linkers for the modification of the side chains, the enzymatically degradable polypeptides, the pH-sensitive Schiff base, and glutathion-sensitive disulfide bonds are used, the process of which is described in detail below. Even though other kinds of polymers can be also used for the design of functional block copolymers, it is not easy to satisfy the low toxicity and biocompatibility requirements, and limited polymers are allowed for practical use. 

Polyacryl- ariiicle Acrylamide was crosslinked by degradable polypeptide, methacryloyl chloride modified poly[N-(2-hydroxyethyl)-I.-glutamidc]. Degradation of crosslinker by papain in PBS buffer. Controlled release of biologically active macromolecules. Trypsin was used as a model protein. Skorda a aL, 993... 

Kabsch, W., Cast, W.H., Schulz, G.E., Lebermann, R., 1977, Low resolution structure of partially trypsin-degraded polypeptide elongation factor, EF-Tu, from Escherichia coli, J. Mol. 

All known eight-stranded a/p-barrel domains have enzymatic functions that include isomerization of small sugar molecules, oxidation by flavin coenzymes, phosphate transfer, and degradation of sugar polymers. In some of these enzymes the barrel domain comprises the whole subunit of the protein in others the polypeptide chain is longer and forms several additional domains. An enzymatic function in these multidomain subunits, however, is always associated with the barrel domain. 

The first example is the plasma-borne retinol-binding protein, RBP, which is a single polypeptide chain of 182 amino acid residues. This protein is responsible for transporting the lipid alcohol vitamin A (retinol) from its storage site in the liver to the various vitamin-A-dependent tissues. It is a disposable package in the sense that each RBP molecule transports only a single retinol molecule and is then degraded. 

Serpins form very tight complexes with their corresponding serine pro-teinases, thereby inhibiting the latter. A flexible loop region of the serpin binds to the active site of the proteinases. Upon release of the serpin from the complex its polypeptide chain is cleaved by the proteinase in the middle of this loop region and the molecule is subsequently degraded. In addition to the active and cleaved states of the serpins there is also a latent state with an intact polypeptide chain that is functionally inactive and does not bind to the proteinase. 

In animals, the enzymes of fatty acid synthesis are components of one long polypeptide chain, the fatty acid synthase, whereas no similar association exists for the degradative enzymes. (Plants and bacteria employ separate enzymes to carry out the biosynthetic reactions.)... 

Neuronal ischemia Calpastatin is degraded by calpain to a membrane-bound 50-kDa polypeptide in ischemic... 

Chaperones bind to exposed hydrophobic surfaces of polypeptide substrates, and through either ATP-dependent or ATP-independent mechanisms facilitate the folding/assembly, intracellular transport, degradation, and activity of polypeptides. 

Edman degradation A method of amino acid sequencing in proteins in which successive V-terminal amino acids are removed from the polypeptide chain and identified. 

Like peptide oligomers, peptoids can be analyzed by HPLC and by mass spectrometry. They can be sequenced by Fdman degradation [13] or by tandem mass spectrometry [14] since, like polypeptides, they conveniently fragment along the main chain amides [15, 16]. 

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