Aspirin acetylation of βLys-82 of human hemoglobin: NMR study of acetylated hemoglobin tsurumai

Abstract

Acetylation of hemoglobin by aspirin and other compounds has been of interest for the development of agents useful for the treatment of sickle cell disease. In the present study, we have used 2D NMR methods in combination with [1- 13C- acetyl]salicylic acid to probe the acetylation sites of hemoglobin A and hemoglobin Tsurumai, a mutant human hemoglobin characterized by a βLys-82-Gln substitution. In contrast to earlier studies by Klotz and coworkers (e.g. Shamsuddin M, Mason RG, Ritchey JM, Honig GR and Klotz KM, Proc Natl Acad Sci USA 71: 4693–4697, 1974) in which it was concluded that βLys-144 is the principal target residue acetylated by aspirin, the present study confirms our previous but less conclusive demonstration (Xu ASL, Macdonald JM, Labotka RJ and London RE, Biochim Biophys Acta 1432: 333–349, 1999) that βLys-82 is the primary acetylation site of aspirin and related agents. The present studies also provide conclusive evidence that acetylation of βLys-82 produces multiple resonances, probably as a consequence of additional acetylation of other sites, particularly βLys-82′ on the second β chain. The present results also resolve the apparent discrepancy between the targets of modification by aspirin and double-headed aspirin analogs, and provide an explanation for the changes in oxygen affinity and aggregation threshold of aspirin-modified hemoglobin previously observed under in vitro conditions. In light of the present identification of the principal site of acetylation, the potential therapeutic benefit of aspirin in the treatment of sickle cell disease is discussed.