Peptides protein cleaved into

While the first 20-30 residues of a peptide can readily be determined by the Edman method, most polypeptides contain several hundred amino acids. Consequently, most polypeptides must first be cleaved into smaller peptides prior to Edman sequencing. Cleavage also may be necessary to circumvent posttranslational modifications that render a protein s a-amino group blocked , or unreactive with the Edman reagent. 

The term polyproteins is used for two different types of entity. The first refers to precursor polypeptides which are cleaved post-translationally into biologically active proteins or peptides of quite different functions. Examples of these include polyproteins of viruses and some prohormones of vertebrates (reviewed in Kennedy, 2000b). The other type is large proproteins which comprise tandem repetitions of identical or similar polypeptides that are post-translationally cleaved into multiple copies of biochemically similar functional entities. The nematode polyprotein allergens/antigens (NPAs) fall into this class (Fig. 16.1). 

Several different types of proteases hydrolyze intact storage proteins first into large fragments and then into smaller peptides and amino acids within the protein body. The peptides are transported to the cytosol where other enzymes, e. g. amino-peptidases, carboxypeptidases, dipeptidases and tripeptidases, cleave them and eventually form a pool of free amino acids [11]. 

Prepro proteins are synthesized with a signal peptide, which directs the protein to the endoplasmic reticulum, where the signal peptide is cleaved thereafter the propeptide is excized and the mature protein or peptide secreted into the circulation. 

In peptide mapping, a protein is enzimatically or chemically cleaved into small peptide fragments, and the resultant mixture is separated by HPLC to generate a peptide map, or fingerprint,... 

The product of gene 8 is the major capsid protein of the filamentous phage. The protein is synthesized as a precursor with an N-terminal extension of 23 amino acids, which is necessary for the insertion of the protein into the bacterial cytoplasmic membrane where the leader peptide is cleaved. During the process of phage assembly, about 2700 copies aggregate around the virus DNA to form a helical array with the amino terminus exposed to the... 

When a protein is cleaved into manageable peptides and the sequence of each peptide is determined, the next problem is that of ordering the peptides themselves in the correct sequence. For this, at least two sets of peptide sequences from different selective cleavage methods are required. 

Paramyxoviruses cause respiratory tract diseases such as croup and pneumonia, as well as measles and mumps. The envelope proteins of these viruses share some features in common with influenza and retroviruses. These similarities include a precursor protein that is cleaved into two fragments, the second of which, called El, bears a fusion peptide at its amino terminus. In addition, peptides from the paramyxovirus FI proteins assemble into stable helical bundles resembling HIV gp41 and influenza HA2 (Baker et al, 1999 Lawless-Delmedico et al, 2000 Zhao et al, 2000). The paramyxovirus F protein differs from influenza HA and retroviral TM... 

Proteins Can Be Specifically Cleaved into Small Peptides to Facilitate Analysis... 

Hydrazinolysis can yield protected peptides for assembly into large peptides or proteins by the azide coupling method. A hmitation is that Bzl esters on Asp and Glu wUl also be converted tBu esters are stable. Boc and For groups on amines are stable, but His(Tos) is cleaved. 

NKT-ceU development is dependent on the protease cathepsin L. As NKT cells react to Lipids, cathepsin L may process a lipid earlier protein that is required for loading lipids onto CD Id. A strong candidate for the lipid carrier protein is prosaposin, a precursor that is cleaved into a series of lipid transfer proteins. As the stmeture of lipids capable of binding CD Id is not as diverse as peptides, it is perhaps not surprising tliat NKT cells exliibit a limited TCR repertoire. The CD Id-restricted NKT cells also differ from mainstream T cells in co-receptor expression. They are CD4 or double negative, and never CD 8". ... 

Fig. 3. Specificity and sites of cleavage of the clostridial neurotoxins. VAMP is bound to the SSV membrane through a single transmembrane domain (black box), with the majority of the protein exposed to the cytoplasm. In addition, VAMP contains an amino-terminal domain rich in proline (hatched box). SNAP-25 and syn-taxin are bound to the target membrane via palmitoylation (SNAP-25) or via a single transmembrane domain (syntaxin). TeTx and BoNT/B, D, F or G act on the conserved central portion of VAMP and release its amino-terminal part into the cytosol. The sequences indicate the peptide bonds cleaved by CNTs on rat VAMP-1 and VAMP-2. BoNT/A and E cleave SNAP-25 at the carboxyl terminus, with the release of nine and twenty-six residues peptides respectively. BoNT/C also cleaves SNAP-25 at the carboxy-terminus, and cleaves syntaxin at a single site near the cytosolic membrane surface. The action of TeTx and BoNT/B, C, D, F and G causes the release of a large portion of the cytosolic domain of VAMP and syntaxin. Conversely, only a small segment of SNAP-25 is released by the selective proteolysis of BoNT/A, C and E...

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