RNA-hydrolyzing activity of human serum albumin and its recombinant analogue.

The comparative analysis of RNA-hydrolyzing activity of albumin from human serum and albumin expressed in methylotrophic yeast Pichia pastoris has been carried out. The rate of polyribonucleotide phosphodiester bond cleavage in the presence of recombinant albumin has been found to be similar to that of the reaction mediated by the native protein. According to 31P NMR data, RNA hydrolysis follows the mechanism of intermolecular trans-esterification to yield 2',3'-cyclophosphodiester reaction products that are further slowly hydrolyzed to form nucleoside-3'- and nucleoside-2'-phosphates. Analysis of pH dependence suggests an acid-base mechanism of catalysis. The catalytic activity and substrate specificity of albumin in RNA hydrolysis distinguish it from human ribonucleases.

Catalytic autoantibodies in clinical autoimmunity and modern medicine.

Abzymes (catalytic autoantibodies) belong to an absolutely new group of physiologically active substances with dual characteristics: they represent a pool of canonical autoantibodies and possess catalytic activity. Among them, proteolytic and DNA-hydrolyzing autoantibodies are of special value. Abzymes are an important pathogenic factor in the progression of clinical autoimmunity syndrome. The presence of autoantibodies against various autoantigens is accompanied by their high catalytic potential. The increase in this activity correlates with serum levels of the autoantibodies, clinical manifestations of autoimmune disorders, disease severity and the rate of progressing disability. Abzymes are crucial for immune homeostasis regulation. They can be of practical value in the development of modern immunodiagnostic tools and schedules of immunotherapy.

Catalytic antibodies in clinical and experimental pathology: human and mouse models.

Most of the data accumulated through studies on natural catalytic autoantibodies indicate that production scales up markedly in pathological abnormalities. We have previously described an increased level of DNA-hydrolyzing autoantibodies in the sera of patients with various autoimmune disorders [systemic lupus erythematosus (SLE), rheumatoid arthritis, scleroderma], HIV infection and lymphoproliferative diseases accompanied by autoimmune manifestations. In the present study, we show that an increased level of catalytic activity of autoantibodies can be observed in the sera of autoimmune mice, thus providing a fundamental insight into the medical relevance of abzymes. Polyclonal autoantibodies purified from sera of NZB/W, MRL-lpr/lpr and SJL/J mice show proteolytic and DNA-hydrolyzing activities, as opposed to those harvested from non-autoimmune BALB/c mice. The expressiveness of the catalytic activity was strongly dependent on the age of the animal. The highest levels of catalytic activity were found in the sera of mice aged between 8 and 12 months; the lowest level was typical of younger animals whose age ranged from 6 to 8 weeks. Specific inhibition assays of the catalytic activities were performed to throw light on the nature of the abzyme activity. Within a cohort of aging animals, a strong correlation between marked autoimmune abnormalities and levels of catalytic activities has been established. Nonimmunized SJL/J mice revealed specific immune responses to myelin basic protein (MBP), skeletal muscle myosin (skMyo) and cardiac myosin (Myo), and highly purified antibodies from their serum show specific proteolytic attack against the target antigens. This finding prompted us to undertake a more detailed study of specific antibody-mediated proteolysis in diseased humans. A targeted catalytic response was originally demonstrated against MBP and Myo in multiple sclerosis and myocarditis patients, respectively.