[Forms of LonB protease from Archaeoglobus fulgidus devoid of the transmembrane domain: the contribution of the quaternary structure to the regulation of enzyme proteolytic activity].

Deletion of the transmembrane domain (TM-domain) of Archaeoglobus flggidus LonB protease (AfLon) was shown to result in uncontrollable activation of the enzyme proteolytic site and in vivo autolysis yielding a stable and functionally inactive fragment consisting of both alpha-helical and proteolytic domains (alphaP). The deltaTM-AfLonTM-S590A enzyme form, obtained by site-directed mutagenesis of the catalytic Ser residue, is capable of recombination with the alphaP fragment. The mixed oligomers were shown to be proteolytically active, which indicates a crucial role of subunit interactions in the activation of the AfLon proteolytic site. The thermophilic nature of AfLon protease was found to be due to the special features of the enzyme activity regulation, the structure of ATPase domain, and the quaternary structure.

[Various aspects of structural studies of aspartate proteinases]. / Nekotorye aspekty strukturnykh issledovanii aspartatnykh proteinaz.

The paper is a brief account of aspartic proteinases' structural studies developed in V.A. Engelhardt Institute of Molecular Biology during the last 3 years. The work on porcine pepsin has been finalized after the refinement of the monoclinic crystal form at 1.8 A resolution performed in collaboration with the group of protein structure and function studies of the University of Alberta in Canada. An important structural property of chymosin which explains the enzyme specificity has been found. Protein engineering work on chymosin is being developed. The structural template for aspartic proteinases has been elucidated and on the basis of this template the model of HIV-1 protease molecule has been built. Some approaches to the design of HIV-1 protease inhibitors were elucidated.

[The structure of pepsin. II. Structure of the enzyme active site (at 2 angstroms resolution)]. / Struktura pepsina. II. Stroenie aktivnogo tsentra fermenta (razreshenie 2 angstrom).

Detailed structure of the pepsin active site in the region of the active aspartic acid residues and substrate binding S1 and S1' sites is considered. At the active site of the enzyme crystals studied several molecules of ethanol were detected, which interact with active groups. The catalytic properties of aspartyl proteinases towards dipeptide substrates were explained on the base of the specific structure of S1 and S1' binding sites.

[X-ray analysis of pepsin. VI. Atomic structure of the enzyme at 2-angstrom resolution]. / Rentgenostrukturnyi analiz pepsina. VI. Atomnaia struktura fermenta pri razreshenii 2 angstrom.

The crystallographic refinement of pepsin structure at 2 A resolution is described. Real space refinement and Jack and Levitt methods were used. As a result, the refined atomic coordinates of 2436 nonhydrogen atoms were obtained. Values of crystallographic R-factor and conformational energy are 29.2% and -1347 kcal/mol correspondingly. The most important and interesting features of pepsin structure are discussed.

[X-ray structural analysis of pepsin. V. Conformation of the main chain of the enzyme]. / Rentgenostrukturnyi analiz pepsina. V. Konformatsiia glavnoi tsepi fermenta.

A detailed description of structural investigations of pepsin from 3.5 to 2.7 A resolution are given. The main attention is drawn to the conformation of the polypeptide backbone of the enzyme. The numbers of amino acid residues involved in the formation of various structural elements are listed. The structure of pepsin is similar to that of acid proteases isolated from lower organisms. The two domain structure of all acid proteases has a periodicity in the sequence of beta-segments and helices and a very specific symmetrical structure of each domain. This makes it possible to describe the structure of acid proteases in simple terms.