K. Adachi et al., POLYMERIZATION OF 3 HEMOGLOBIN A(2) VARIANTS CONTAINING VAL(DELTA-6) AND INHIBITION OF HEMOGLOBIN-S POLYMERIZATION BY HEMOGLOBIN A(2), The Journal of biological chemistry, 271(40), 1996, pp. 24557-24563
To understand determinants for hemoglobin (Hb) stability and Hb A(2) i
nhibition of Hb S polymerization, three Val(delta 6) Hb A(2) variants
(Hb A(2) delta E6V, Hb A(2) delta E6V, delta Q87T, and Hb A(2) delta E
6V, delta A22E, delta Q87T) were expressed in yeast, and stability to
mechanical agitation and polymerization properties were assessed. Oxy
forms of Hb A(2) delta E6V and Hb A(2) delta E6V, delta Q87T were 2- a
nd 1.6-fold, respectively, less stable than oxy-Hb S, while the stabil
ity of Hb A(2) delta E6V, delta A22E, delta Q87T was similar to that o
f Hb S, suggesting that Ala(delta 22) and Gln(delta 87) contribute to
the surface hydrophobicity of Rb A(2). Deoxy Hb A(2) delta E6V polymer
ized without a delay time, like deoxy Hb F gamma EGV, while deoxy Hb A
(2) delta E6V, delta Q87T and deoxy Hb A(2) delta E6V, delta A22E, del
ta Q87T polymerized after a delay time, like deoxy Hb S, suggesting th
at beta 87 Thr is required for the formation of nuclei. Deoxy Hb F gam
ma E6V, gamma Q87T showed no delay time and required a 3.5-fold higher
concentration than deoxy Hb S for polymerization, suggesting that Thr
effects on Val(delta 6) Hb A(2) and Val(gamma 6) Hb F variants are di
fferent. Mixtures of deoxy Hb S/Hb A(2) delta E6V, delta Q87T polymeri
zed, like deoxy Hb S, while polymerization of Hb S/Hb A(2) delta E6V m
ixtures was inhibited, like Hb S/Hb F gamma E6V mixtures. These result
s suggest alpha(2) beta(S) delta(6 Val, 87 Thr) hybrids and Hb A(2) de
lta E6V, delta 87T participate in Hb S nucleation, while only 50% of a
lpha(2) beta(S) delta(6Val) hybrids and none of the Hb A(2) delta E6V
participate. These findings are in contrast to those of mixtures of Hb
S with Hb F gamma E6V or Hb F gamma E6V, Q87T, which both inhibit Hb
S polymerization. Our results also suggest participation in nucleation
of some alpha(2) beta(S) delta hybrids in A(2)S mixtures but not alph
a(2) beta(S) gamma hybrids in FS mixtures.