Liquid–liquid separation in solutions of normal and sickle cell hemoglobin

We show that in solutions of human hemoglobin (Hb)—oxy- and deoxy-Hb A or S—of near-physiological pH, ionic strength, and Hb concentration, liquid–liquid phase separation occurs reversibly and reproducibly at temperatures between 35 and 40°C. In solutions of deoxy-HbS, we demonstrate that the dense liquid droplets facilitate the nucleation of HbS polymers, whose formation is the primary pathogenic event for sickle cell anemia. In view of recent results that shifts of the liquid–liquid separation phase boundary can be achieved by nontoxic additives at molar concentrations up to 30 times lower than the protein concentrations, these findings open new avenues for the inhibition of the HbS polymerization.

我们发现，在接近生理pH值、离子强度及血红蛋白（hemoglobin, Hb）浓度的人类血红蛋白溶液（涵盖氧合型与脱氧型Hb A或Hb S）中，液-液相分离（liquid–liquid phase separation）可在35至40℃的温度范围内可逆且可重复地发生。在脱氧Hb S溶液中，我们证实致密液滴可促进Hb S聚合物的成核过程，而该聚合物的形成正是镰状细胞贫血（sickle cell anemia）的核心致病事件。鉴于近期研究表明，通过摩尔浓度最高可较蛋白质浓度低30倍的无毒添加剂，即可调控液-液相分离相界（liquid–liquid separation phase boundary）的位置，上述发现为Hb S聚合的抑制开辟了全新途径。