Actin carbonylation: From a simple marker of protein oxidation to relevantsigns of severe functional impairment

The number of protein-bound carbonyl groups is an established marker of pro tein oxidation. Recent evidence indicates a significant increase in actin c arbonyl content in both Alzheimer's disease brains and ischemic hearts. The enhancement of actin carbonylation, causing the disruption of the actin cy toskeleton and the loss of the barrier function, has also been found in hum an colonic cells after exposure to hypochlorous acid (HOCI). Here, the effe cts of oxidation induced by HOCI on purified actin are presented. Results s how that HOCI causes a rapidly increasing yield of carbonyl groups. However , when carbonylation becomes evident, some Cys and Met residues have been a lready oxidized. Covalent intermolecular cross-linking as well as some nonc ovalent aggregation of carbonylated actin have been found. The covalent cro ss-linking, unaffected by reducing and denaturing agents, parallels an incr ease in dityrosine fluorescence. Moreover, HOCI-mediated oxidation induces the progressive disruption of actin filaments and the inhibition of F-actin formation. The molar ratios of HOCI to actin that lead to inhibition of ac tin polymerization seem to have effect only on cysteines and methionines. T he process that involves oxidation of amino acid side chains with formation of a carbonyl group would occur at an extent of oxidative insult higher th an that causing the oxidation of some critical amino acid residues. Therefo re, the increase in actin content of carbonyl groups found in vivo would in dicate drastic oxidative modification leading to drastic functional impairm ents. (C) 2001 Elsevier Science Inc.