Probing the Role of Cytoglobin's Extended Termini

Cytoglobin (Cygb) is a hexacoordinated heme protein that is expressed ubiquitously in vertebrate tissues. The physiological function of Cygb remains unknown; however it has been proposed to have a role in oxygen sensing, lipid peroxidation and NO metabolism. Structurally, Cygb has a unique feature among vertebrate globins including extended, disordered N- and C- termini. Although the function of the terminal extensions remains to be determined, their role in promoting intracellular interactions has been proposed. In order to probe the impact of the N- and C- termini on the functional and structural properties of Cygb, human Cygb (hCygb) with truncated N-terminal (hCygb ΔN), C-terminal (hCygb ΔC) and N- and C- termini (hCygb ΔNΔC) were studied using various spectroscopic techniques. The presence of the N- termini increases the stability of Cygb by 13°C. In addition, all studied forms of Cygb bind 1-anilino-8-napthalene sulphonate hydrophobic probe, although the affinity for 1,8-ANS increases in the absence of the N- and C- termini suggesting that the deletion of the N- and C- termini leads to the exposure of the hydrophobic sites on the protein surface. Furthermore, the impact of the extended N- and C- termini on Cygb interactions with small gaseous ligands will be discussed.