Resistance to proteolysis

Some research groups prefer IgAs because they are more stable than IgGs and more resistant to proteolysis. Plants can assemble secretory IgAs, which consist of... 

Proteins differ greatly in their intrinsic susceptibility to proteolytic attack. Resistance to proteolysis seems to be dependent upon higher levels of protein structure (i.e. secondary and tertiary structure), as tight packing often shields susceptible peptide bonds from attack. Denaturation thus renders proteins very susceptible to proteolytic degradation. 

The existence of flexible regions in ribosomal proteins can be explored by studying the action of proteolytic enzymes under mild conditions. It has been found that many E. coli ribosomal proteins consist of two domains one compactly folded and resistant to proteolysis, the other flexible and vulnerable to proteases (Littlechild et al, 1983). Some proteins (S15, S16, S17, and L30) are very resistant whereas others (S2, S6, S9, L2, L27, L29, and L33) are completely degraded without the appearance of discrete fragments. The remaining proteins yield fragments of various size under these conditions. 

One of the questions evolving from the results of Chapters 3 and 5 is If C(, sugars are not involved in the Maillard reaction, which compounds are In addition, is the glycosylated dentin as resistant to proteolysis by cariogenic bacteria as it is to pepsin in vitro ... 

No differences were found between the native and deglycosylated enzymes for the characteristics of pH range of stability, optimum pH, and adsorption to cellulose and milled wood. It can be concluded that the most important role of the carbohydrate chains in laccase III is the resistance to proteolysis in wood decay (15),... 

Similar conclusions may be reached from the study of the ligand-induced resistance to proteolysis (47, 53), a phenomenon that has been employed in the production of large complementing fragments of nuclease (see below). 

Binding of thyinidine-3, 5 -diphosphate (pdTp) and Ca-+ to nuclease induces resistance to proteolysis by a number of proteases (47, 53). Trypsin rapidly cleaves the peptide bond between residues 5 and 6 of the liganded nuclease. The fragment thus formed, nuclease-(6-149), possesses enzymic activity and structure similar to nuclease (48)- Further cleavage of nuclease-(6-149) in the presence of the ligands takes place... 

Mass spectroscopy (MS) methods can be used to analyze complex mixtures of proteins and peptides in minutes and with mass accuracy several orders of magnitude better than that obtained from electrophoretic methods. For proteins with a known sequence, the mass measurement accuracies are generally sufficient to identify the products resistant to proteolysis precisely and to define compact domains within proteins effectively. 

Conversely, the connective tissues and cartilage are much more resistant to proteolysis and will survive for a longer period of time, although they too will eventually succumb to the effects of putrefaction. Reticulin, epidermis, and muscle protein will resist breakdown for some time, whereas collagen and keratin may survive for longer periods (Linch and Prahlow 2001). Keratin is an insoluble fibrous protein found in the skin, hair, and nails, and its resistance to attack by most proteolytic enzymes (Gupta and Ramnani 2006) is the reason it is often found intact amongst skeletal remains, particularly in burial environments (Macko et al. 1999). 

The greatest problem connected to gluten protein immunoreactivity as well as with peptides which are responsible for inflammatory states in celiac disease is the presence of peptides containing proline that are resistant to proteolysis. The group of specific enzymes is required for hydrolysis of peptide bonds in which proline residue is present (Hausch et al., 2003). 

Other measures of protein flexibility have been found to correlate with thermal stability. One is resistance to proteolysis (Daniel et al., 1982 Fontana, 1988). Another is the quenching of buried tryptophan fluorescence by acrylamide, used in a study by Varley and Pain (1991). Both these processes are mediated by the same combination of local and global unfolding events that determine rates of hydrogen exchange. Their rates will depend on the ability of another molecule, acrylamide or a proteolytic enzyme, to penetrate into normally buried regions of the protein in order to either quench fluorescence or cleave peptide bonds. 

The selection efficiency is also dependent on the percentage of phage(mid) particles which display a particular antibody. This usually varies between 1 % and 10%, although it can be far lower [14]. The selection of two antibodies with similar affinities but different display levels will result in the preferential recovery of the antibody with the highest display level. The level of display is the result of a number of different parameters, including (1) antibody folding within the periplasm, (2) resistance to proteolysis, (3) resistance to aggregation, and (4) toxicity to the bacterial expression host. 

In conjunction with research on protein extraction from yeast, we investigated methods for the maximum recovery of protein possessing good functional properties but low in nucleic acid. Therefore, we examined the feasibility of making the yeast protein resistant to proteolysis during extraction and nucleic acid reduction. Using established extraction procedures (76), we observed... 

The stability of the /3-barrel itself was demonstrated in engineering experiments with OmpA. The four external loops of OmpA were replaced by shortcuts in all possible combinations (Koebnik, 1999). The resulting deletion mutants lost their biological functions in bacterial / -conjugation and as bacteriophage receptors, but kept the transmembrane /1-barrel as demonstrated by their resistance to proteolysis and thermal denaturation. The results confirm the expectation that the large external loops do not contribute to /1-barrel folding and stability. 

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