Chymotrypsinogen folding

Figure 11.7 Schematic diagram of the structure of chymotrypsin, which is folded into two antiparallel p domains. The six p strands of each domain are red, the side chains of the catalytic triad are dark blue, and the disulfide bridges that join the three polypeptide chains are marked in violet. Chain A (green, residues 1-13) is linked to chain B (blue, residues 16-146) by a disulfide bridge between Cys 1 and Cys 122. Chain B is in turn linked to chain C (yellow, residues 149-245) by a disulfide bridge between Cys 136 and Cys 201. Dotted lines indicate residues 14-15 and 147-148 in the inactive precursor, chmotrypsinogen. These residues are excised during the conversion of chymotrypsinogen to the active enzyme chymotrypsin.

Chymotrypsinogen consists of a single 245-residue chain. The amino acid residues in chymotrypsin, trypsin, and elastase are usually all numbered according to their position in this zymogen. Inactive proenzymes are formed as precursors to enzymes of many different classes and are activated in a variety of ways. A part of the polypeptide chain of the proenzymes is often folded over the active site, interacting in a nonsubstrate-like fashion and blocking the site.197a... 

Chymotrypsinogen 480, 481 Chymotrypsin inhibitor 2 (CI2) folding kinetics 544-577, 577 GroEL binding 605 fragments 577, 578, 587, 588, 595 mechanism of folding 576-588 structure 576, 577 Circular dichroism (CD) 193-195 optimal absorbance for signal to noise 212-214... 

The inactive precursors are called trypsinogen, pepsinogen, chymotrypsino-gen, and procarboxypeptidase. These precursors are converted to the active enzymes by hydrolytic cleavage of a few specific peptide bonds under the influence of other enzymes (trypsin, for example, converts chymotrypsinogen to chymotrypsin). The digestive enzymes do not appear to self-destruct, probably because they are so constructed that it is sterically impossible to fit a part of one enzyme molecule into the active site of another. In this connection, it is significant that chymotrypsin attacks denatured proteins more rapidly than natural proteins with their compact structures of precisely folded chains. 

Bovine procarboxypeptidase B has been purified from pancreatin extracts (50). However, after a twenty-fold purification according to the technique described, the preparation still contains large amounts of chymotrypsinogen B (52). Final purification must therefore involve chromatography as well as fractional precipitations and extractions. 

The disulfide bond in a-chymotrypsinogen A is reduced about 2.3-fold faster using BMS and DMH than by DTT (Table I). A maximum of 0.75 disulfide group per a-chymotrypsinogen A molecule was reduced under the reduction conditions. The apparent rate constant for the reduction of disulfide bond in... 

Chymotrypsin is formed from a precursor molecule called chymotrypsinogen, which has 245 amino acid residues. Cleavage of two dipeptide units of chymotrypsinogen produces chymotrypsin. Chymotrypsin folds in a way that brings together histidine at position 57, aspartic acid at position 102, and serine at position 195. Together, these residues constitute what is called the catalytic triad of the active site (Fig. 24.18). Near the active... 

A study of the mechanical properties ( mechanochemistry ) of immobilized enzymes (e.g. chymotrypsinogen trapped within a polyacrylamide gel) has provided a means whereby the chemical processes at a molecular level can be controlled by mechanical compression and decompression of the supporting gel (i.e. by controlling the pore size). Mechanical compression of a chymotrypsinogen-polyacrylamide gel resulted in a 20-fold increase in the diffusion-controlled tryptic activation of chymotrypsinogen, the reaction rate... 

This method can be used for mapping native proteins. Its rapidity also allows one to follow kinetics of protein folding and unfolding. It was used by Ghelis (1971) and Ghelis and co-workers (1975) to detect local conformational differences resulting from activation of chymotrypsinogen into chymotrypsin and from the alkaline conformational transition of the enzyme. 

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