Antibodies to H2a and H2b histones from the sera of HIV-infected patients catalyze site-specific degradation of these histones

Abstract

Histones and their post-translational modifications have key roles in chromatin remodeling and gene transcription. Besides intranuclear functions, histones act as damage-associated molecules when they are released into the extracellular space. Administration of histones to animals leads to systemic inflammatory and toxic responses. Autoantibodies with enzymatic activities (abzymes) are distinctive features of some autoimmune and viral diseases. Electrophoretically homogeneous IgGs containing no canonical enzymes were isolated from the sera of HIV-infected patients by chromatography on several affinity sorbents including anti-histone Sepharose. In contrast to canonical proteases (trypsin, chymotrypsin, proteinase K), IgGs from HIV-infected patients specifically hydrolyzed only histones but not many other tested globular proteins. Using MALDI mass spectrometry the sites of H2a and H2b histone cleavage by anti-histone IgGs were determined for the first time. One cluster of H2a hydrolysis contains two major (↕) and four moderate (↓) cleavage sites: 31-H↓R↓L↓L↓R↕K G↕N-38. One major and two moderate sites of cleavage were revealed in the second cluster: 14-A↕KSRS↓SRA↓G-22. The third cluster corresponding to the H2a C-terminal part contains only five minor (†) sites of cleavage: 82-H†LQLAIRNDEELN†KLLG†RV†T†I-102. It was shown that two major and four moderate sites of cleavage were present in the main cluster of H2b hydrolysis: 46-K↕QvhpD↓TgiS↓SkA↓M↕GiM↓N-63. Two moderate sites of cleavage correspond to a relatively short 6-mer cluster: 12-K↓GskK↓A-17. The third relatively long 9-mer cluster contains one major and two minor sites of H2b cleavage: 80-L↕AHYN†KRS†T-88. In the nucleosome core particle, most of the major and moderate cleavage sites are located at the H2a/H2b interaction interface. Minor cleavage sites of H2a are involved in binding with H3 in the nucleosome core. Two moderate cleavage sites of H2b and one major cleavage site of H2a are located in the disordered N-terminal region interacting with DNA. According to the crystal structure of the nucleosome core particle, all identified cleavage sites are expected to affect H2a and H2b folding, nucleosome assembly, and binding of H2a and H2b with DNA. The existence of H2a and H2b hydrolyzing abzymes may be very important for the further understanding of unknown possibilities of immune systems and biological functions of antibodies.

Autoantibodies in HIV‐infected patients: Cross site‐specific hydrolysis of H1 histone and myelin basic protein

“…It should be assumed that analogous regularities can also occur in the case of sequence‐dependent proteases. Therefore, it is not surprising that proteolytic antiprotein abzymes usually catalyze only their specific proteins .…”

“…Apoptotic cells are considered as the primary antigens and immunogens sources in SLE, MS, and other AI pathologies [23]. Antibodies hydrolyzing all five human histones (H1, H2a, H2b, H3, and H4) were revealed in the sera of HIV-infected patients [24][25][26][27].…”

“…HIV-dependent activation of B lymphocytes results in the production of auto-Abs to many various human cell components [28,32,36,37]. In addition, IgGs and/or IgMs from sera of AIDS patients hydrolyze DNA [38], HIV-1 reverse transcriptase [39], integrase [40][41][42][43], and histones [24][25][26][27]. It was shown that 100% of IgGs of 32 HIV-infected patients efficiently cleavage from one to five human histones [24][25][26][27].…”

“…In addition, IgGs and/or IgMs from sera of AIDS patients hydrolyze DNA [38], HIV-1 reverse transcriptase [39], integrase [40][41][42][43], and histones [24][25][26][27]. It was shown that 100% of IgGs of 32 HIV-infected patients efficiently cleavage from one to five human histones [24][25][26][27]. Thus, abzymes against histones can play an important negative role in the pathogenesis of AIDS and probably in the development of different various AI diseases.…”

“…It was shown that MBPhydrolyzing activity is an intrinsic property of antibodies from the blood of HIV-infected patients. As mentioned above, the abzymes against any protein usually specifically hydrolyze only this, but not other control proteins [3][4][5]; according to previous data only anti-MBP antibodies hydrolyze MBP [13][14][15][19][20][21], while histones are split only by anti-histones abzymes [24][25][26][27]. Till yet in the literature, there were no data on cross-hydrolysis of proteins with antibodies against different proteins [3][4][5][6][7][8][9][10][11][12][13][14][15].…”