Surface and interface β-chain residues synergistically affect hemoglobin assembly

Homo- and heterotetramer formations of beta 112 variants (beta(112Cys-->Asp), beta(112Cys-->Ser), beta(112Cys-->Thr), and beta(112Cys-->Val)) of hemoglobin were characterized in the presence and absence of beta(16Gly-->Asp) in vitro. In all cases an alteration in overall surface charge (beta(16Gly-->Asp)) decreased the beta(4) homotetramer stability (association constants as determined by gel-permeation chromatography) albeit to differing extents. In contrast, competition experiments of hemoglobin subunits showed that heterotetramer formation was promoted by this substitution. Order of increase in tetramer formation by the additional negative surface charge in the beta 112 variants was as follows: Hb beta G16D, C112D > Hb beta G16D, C112S > Hb beta G16D > Hb G16D, C112T > Hb beta G16D, C112V, Thus, the overall surface charge of the beta chain and its contribution to electrostatic interaction in these instances appear to act in synergy with alpha(1)beta(1) interface residues to affect the assembly of hemoglobin molecules. (C) 2000 Academic Press.