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Antibodies against H3 and H4 histones from the sera of HIV‐infected patients catalyze site‐specific degradation of these histones

Histones and their posttranslational modified forms play pivotal roles in chromatin functioning and gene transcription. Also, histones are harmful when they enter the intercellular space; their administration to animals results in systemic inflammatory and toxic responses. Autoantibodies having enzymatic activities (abzymes) are the specific feature of several autoimmune and viral diseases. Electrophoretically homogeneous IgGs containing no canonical proteases were purified from sera of HIV‐infected patients by using several affinity chromatographies. In contrast to known canonical proteases, Abs from HIV‐infected patients hydrolyzed exclusively only histones but no other control globular proteins. The H3 and H4 histone cleavage sites by antihistone IgGs were determined by matrix‐assisted laser desorption/ionization mass spectrometry for the first time. Two clusters of H3 hydrolysis contain major (↕) and minor (*) cleavage sites: 18‐K*Q*LA↕TK*A↕AR*KS↕A*P‐30 and 34‐G*VK*KPHR*YRPGTVA*L*R‐50. H4 histone has only 1 cluster of cleavage sites containing additionally moderate (↓) cleavage sites: 15‐A↕KR↕HR↕KVLR↓D*NIQ↓GIT*K‐31. Sites of these histones cleavage correspond mainly to their known epitopes. It was surprising that most of the cleavage sites of histones are involved in the interaction with DNA of nucleosome core. Because histones act as damage‐associated molecules, abzymes against H3 and H4 can play important role in pathogenesis of AIDs and probably other viral and immune diseases.