Abstract:
The active site of the aspartic proteinase, endothiapepsin, has been defined by X-ray analysis and restrained least-squares refinement at 2.1 A resolution with a crystallographic agreement value of 0.16. The environments of the two catalytically important aspartyl groups are remarkably similar and the contributions of the NH2- and COOH-terminal domains to the catalytic centre are related by a local 2-fold axis. The carboxylates of the aspartyls share a hydrogen bond and have equivalent contacts to a bound water molecule or hydroxonium ion lying on the local diad. The main chains around 32 and 215 are connected by a novel interaction involving diad-related threonines. It is suggested that the two pKa values of the active site aspartyls arise from a structure not unlike that in maleic acid with a hydrogen-bonded intermediate species and a dicarboxylate characterised by electrostatic repulsions between the two negatively charged groups.
More Related Videos
Related Concept Videos
Amino acids
The Proteasome
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...
Allosteric Proteins-ATCase
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
Caspases
The Proteasome
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. This involves participation of a series of enzymes including— E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3 (ubiquitin...
The Proteasome Structure
The proteasome is an...


