Alexander G. Gabibov

Selected publications

  1. Zakharova M.Y., Kuznetsov N.A., Dubiley S.A., Kozyr A.V., Fedorova O.S., Chudakov D.M., Knorre D.G., Shemyakin I.G., Gabibov A.G., Kolesnikov A.V. (2009). Substrate recognition of anthrax lethal factor examined by combinatorial and pre-steady-state kinetic approaches. J. Biol. Chem. 284 (27), 17902–13 [+]

    Lethal factor (LF), a zinc-dependent protease of high specificity produced by Bacillus anthracis, is the effector component of the binary toxin that causes death in anthrax. New therapeutics targeting the toxin are required to reduce systemic anthrax-related fatalities. In particular, new insights into the LF catalytic mechanism will be useful for the development of LF inhibitors. We evaluated the minimal length required for formation of bona fide LF substrates using substrate phage display. Phage-based selection yielded a substrate that is cleaved seven times more efficiently by LF than the peptide targeted in the protein kinase MKK6. Site-directed mutagenesis within the metal-binding site in the LF active center and within phage-selected substrates revealed a complex pattern of LF-substrate interactions. The elementary steps of LF-mediated proteolysis were resolved by the stopped-flow technique. Pre-steady-state kinetics of LF proteolysis followed a four-step mechanism as follows: initial substrate binding, rearrangement of the enzyme-substrate complex, a rate-limiting cleavage step, and product release. Examination of LF interactions with metal ions revealed an unexpected activation of the protease by Ca(2+) and Mn(2+). Based on the available structural and kinetic data, we propose a model for LF-substrate interaction. Resolution of the kinetic and structural parameters governing LF activity may be exploited to design new LF inhibitors.

  2. Reshetnyak A.V., Armentano M.F., Ponomarenko N.A., Vizzuso D., Durova O.M., Ziganshin R., Serebryakova M., Govorun V., Gololobov G., Morse H.C. 3rd, Friboulet A., Makker S.P., Gabibov A.G., Tramontano A. (2007). Routes to covalent catalysis by reactive selection for nascent protein nucleophiles. J. Am. Chem. Soc. 129 (51), 16175–82 [+]

    Reactivity-based selection strategies have been used to enrich combinatorial libraries for encoded biocatalysts having revised substrate specificity or altered catalytic activity. This approach can also assist in artificial evolution of enzyme catalysis from protein templates without bias for predefined catalytic sites. The prevalence of covalent intermediates in enzymatic mechanisms suggests the universal utility of the covalent complex as the basis for selection. Covalent selection by phosphonate ester exchange was applied to a phage display library of antibody variable fragments (scFv) to sample the scope and mechanism of chemical reactivity in a naive molecular library. Selected scFv segregated into structurally related covalent and noncovalent binders. Clones that reacted covalently utilized tyrosine residues exclusively as the nucleophile. Two motifs were identified by structural analysis, recruiting distinct Tyr residues of the light chain. Most clones employed Tyr32 in CDR-L1, whereas a unique clone (A.17) reacted at Tyr36 in FR-L2. Enhanced phosphonylation kinetics and modest amidase activity of A.17 suggested a primitive catalytic site. Covalent selection may thus provide access to protein molecules that approximate an early apparatus for covalent catalysis.

  3. Ponomarenko N.A., Durova O.M., Vorobiev I.I., Belogurov A.A. Jr, Kurkova I.N., Petrenko A.G., Telegin G.B., Suchkov S.V., Kiselev S.L., Lagarkova M.A., Govorun V.M., Serebryakova M.V., Avalle B., Tornatore P., Karavanov A., Morse H.C. 3rd, Thomas D., Friboulet A., Gabibov A.G. (2006). Autoantibodies to myelin basic protein catalyze site-specific degradation of their antigen. Proc. Natl. Acad. Sci. U.S.A. 103 (2), 281–6 [+]

    Autoantibody-mediated tissue destruction is among the main features of organ-specific autoimmunity. This report describes "an antibody enzyme" (abzyme) contribution to the site-specific degradation of a neural antigen. We detected proteolytic activity toward myelin basic protein (MBP) in the fraction of antibodies purified from the sera of humans with multiple sclerosis (MS) and mice with induced experimental allergic encephalomyelitis. Chromatography and zymography data demonstrated that the proteolytic activity of this preparation was exclusively associated with the antibodies. No activity was found in the IgG fraction of healthy donors. The human and murine abzymes efficiently cleaved MBP but not other protein substrates tested. The sites of MBP cleavage determined by mass spectrometry were localized within immunodominant regions of MBP. The abzymes could also cleave recombinant substrates containing encephalytogenic MBP(85-101) peptide. An established MS therapeutic Copaxone appeared to be a specific abzyme inhibitor. Thus, the discovered epitope-specific antibody-mediated degradation of MBP suggests a mechanistic explanation of the slow development of neurodegeneration associated with MS.

  4. Ponomarenko N.A., Vorobiev I.I., Alexandrova E.S., Reshetnyak A.V., Telegin G.B., Khaidukov S.V., Avalle B., Karavanov A., Morse H.C. 3rd, Thomas D., Friboulet A., Gabibov A.G. (2006). Induction of a protein-targeted catalytic response in autoimmune prone mice: antibody-mediated cleavage of HIV-1 glycoprotein GP120. Biochemistry 45 (1), 324–30 [+]

    We have induced a polyclonal IgG that degrades the HIV-1 surface antigen, glycoprotein gp120, by taking advantage of the susceptibility of SJL mice to a peptide-induced autoimmune disorder, experimental autoimmune encephalomyelitis (EAE). Specific pathogen-free SJL mice were immunized with structural fragments of gp120, fused in-frame with encephalitogenic peptide MBP(85-101). It has resulted in a pronounced disease-associated immune response against antigens. A dramatic increase of gp120 degradation level by purified polyclonal IgG from immunized versus nonimmunized mice has been demonstrated by a newly developed fluorescence-based assay. This activity was inhibited by anti-mouse immunoglobulin antibodies as well as by Ser- and His-reactive covalent inhibitors. A dominant proteolysis site in recombinant gp120 incubated with purified polyclonal IgG from immunized mice was shown by SDS-PAGE. The SELDI-based mass spectrometry revealed that these antibodies exhibited significant specificity toward the Pro484-Leu485 peptide bond. The sequence surrounding this site is present in nearly half of the HIV-I variants. This novel strategy can be generalized for creating a catalytic vaccine against viral pathogens.

  5. Shuster A.M., Gololobov G.V., Kvashuk O.A., Bogomolova A.E., Smirnov I.V., Gabibov A.G. (1992). DNA hydrolyzing autoantibodies. Science 256 (5057), 665–7 [+]

    A DNA-nicking activity was detected in the sera of patients with various autoimmune pathologies and was shown to be a property of autoantibodies. The DNA hydrolyzing activity, which was purified by affinity and high-performance liquid chromatography, corresponded in size to immunoglobulin M (IgM) and IgG and had a positive response to antibodies to human IgG. The DNA hydrolyzing autoantibodies were stable to acid shock and yielded a DNA degradation pattern that was different from that of deoxyribonuclease (DNase) I and blood DNase.