The mechanism of action of aspartic proteases involves ‘push‐pull’ catalysis

Abstract

In accord with the available kinetic and X-ray crystallographic data, it is proposed that the two catalytically competent carboxyl groups of aspartic proteases constitute a functional unit which mediates the proton from the attacking water molecule to the leaving nitrogen atom of the substrate. Protonation of this nitrogen atom has been the main issue of the previous mechanistic proposals. The first step of the present mechanism involves proton transfer from the water to the aspartic diad and concurrently another proton transfer from the diad to the carbonyl oxygen of the scissile peptide bond. These proton transfers provide the driving force for the bond formation between the substrate and water, which leads to the formation of a tetrahedral intermediate. The intermediate breaks down to products by a similar facilitation, i.e. by concerted general acid-base catalysis, which involves simultaneous proton transfers from the intermediate to the diad and from the diad to the leaving nitrogen of the substrate. The symmetrical mechanism of the formation and decomposition of the tetrahedral adduct resembles that found in the serine protease catalysis.Pepsin; Aspartic protease; Enzyme mechanism Aspartic proteases include several important enzymes, such as pepsin, chymosin, renin, cathepsin D and the proteases isolated from numerous fungi. The amino acid sequences of all these enzymes are homologous, in particular around the active-site residues. Comprehensive reviews on aspartic proteases have been published [1][2][3]. The threedimensional structure of pepsin [4] and three microbial aspartic proteases including penicillopepsin [5,6], Rhizopus chinensin protease [7] and Endothiaparasitica protease [7] has been reported. The tertiary structures of pepsin and the microbial Correspondence address: L. Polg~ir,

Electrostatic Basis of Enzyme Catalysis

“…They are optimally active at acidic pH and have two aspartate side chains at the active site (Hsu et al, 1977;Subramanian et al, 1977). At present no consensus exists on the mechanism of action of aspartic proteases (Fruton, 1987;Bott et al, 1982;James and Sielecki, 1985;Polgár, 1987). All aspartic proteases appear to be highly conserved in that they all have two active aspartyl residues buried in a cleft that is large enough to accommodate polypeptides of about seven amino acid residues.…”

The Structure and Function of the Aspartic Proteinases

“…THE CATALYTIC ASPARTIC ACIDS The mechanism of action of the aspartic proteinases has gradually become the subject of many reviews and dis cussions (17,28,29,39,49,51,70,71,76,92). Several studies unsuccessfully attempted to demonstrate the existence of covalent intermediates in the reaction (22,29,41).…”

Evaluation of Rumex Vesicarius Linn and Symplocos Racemosa Roxb as Probable Hiv-Protease Inhibitors

“…20 Aspartic proteases include pepsin, cathepcin D, renin, chymosin and the proteases isolated from numerous fungi. 21 In the present study, pepsin was used as a substitute for HIV protease for screening possible HIV protease inhibitory activity of the selected plants. So we can use the cheapest substitute of HIV-protease.…”