Hemoglobin subunit beta cysteine 93 (Cysβ93)

Hemoglobin subunit beta cysteine 93 (Cysβ93) is a highly conserved and reactive amino acid residue located on the surface of the hemoglobin molecule. It plays a critical role in the 'third gas' function of hemoglobin, specifically the transport and delivery of nitric oxide (NO) through the formation of S-nitrosohemoglobin (SNO-Hb) (Stamler et al., Science, 1997). This S-nitrosylation mechanism allows hemoglobin to act as a dynamic regulator of vascular tone, promoting vasodilation in regions of low oxygen tension (Zhang et al., PNAS, 2015). Beyond its role in NO signaling, Cysβ93 is a key site for allosteric modulation; its modification can stabilize the high-affinity oxygenated (R) state of hemoglobin. This property makes it a significant focal point for therapeutic strategies in sickle cell disease, where stabilizing the R-state prevents the polymerization of deoxygenated sickle hemoglobin (HbS). Additionally, Cysβ93 is susceptible to oxidative stress and can form mixed disulfides, serving as a redox sensor within the erythrocyte (UniProt P68871).

Other names

Cys93(beta)Beta-93 cysteineHBB Cys93Cysteine 93 of the beta-globin chainReactive cysteine of hemoglobin

Allosteric stabilization of the R-state (oxygenated) hemoglobin and formation of S-nitrosohemoglobin for nitric oxide delivery.