Engineered chimeras reveal the structural basis of hexacoordination in globins: A case study of neuroglobin and myoglobin

Abstract

While these results confirm the regulatory role of the CD region for bis-histidyl hexacoordination, they also suggest that additional sources contribute to fine tune the equilibrium. General significance Globins constitute a ubiquitous group of heme proteins widely found in all kingdoms of life. These findings raise challenging questions regarding the structure-function relationships in these proteins, as bis-histidyl hexacoordination emerges as a novel regulatory mechanism of the physiological function of globins.

Proximal and distal control for ligand binding in neuroglobin: role of the CD loop and evidence for His64 gating

“…An increased velocity of the Gly-loop/F106A mutant in CO binding might be a consequence of the presence of some pentacoordinated species due to the modification of the CD loop 22 . However, resonance Raman spectroscopy did not reveal any pentacoordinated species in the ferrous form or in the photolyzed CO sample (Supplementary Fig.…”

“…Tyr44, in the CD loop, is an important heme-interacting residue involved in regulating binding kinetics 21 since its mutation into an aspartate yielded a 15-fold increase in O 2 binding velocity and a 1.5-fold increase in O 2 affinity. Finally, the CD loop was shown to be involved in the fine tuning of iron coordination by swapping CD corners of human Ngb and sperm whale Mb (swMb), which led to gain of hexa-coordination in swMb 22 .…”

An intramolecular disulfide bond designed in myoglobin fine-tunes both protein structure and peroxidase activity

“…These observations are different from the introduction of the entire C-D region of Ngb into Mb, which showed that the modified Mb adopted a bis-His coordination state at both ferric (413, 535, 565 nm) and ferrous (424, 528, 556 nm) states. [29] These findings indicate that not only the intramolecular disulfide bond, but also the other residues in the C-D region control the heme coordination state of Mb. This is also true for Ngb, since Xray crystal structure shows that both WT Ngb and a mutant C46G/C55S/C120S Ngb, in which the disulfide bond was removed, are in bis-His heme coordination state.…”

“…The C-D region (two short helices and a long loop) of the globin family have been shown to play a crucial role in regulating the heme coordination state and ligand binding to the heme iron. [16,28] Recently, Nadra, Estrin and co-workers [29] engineered a chimeric protein of Mb and Ngb by replacing the entire C-D region of Mb with that of Ngb where the disulfide bond of Cys46-Cys55 locates, and revealed the regulatory role of the entire C-D region in Ngb for bis-His coordination.…”

Structural and functional properties of Antarctic fish cytoglobins-1: Cold-reactivity in multi-ligand reactions

“…Such difference may thus depend on distributed subtle details, as often suggested by the comparison of thermostable protein structures with their mesophilic homologues. Additionally, a key contributing factor may reside in the dynamics of selected structural elements, or of the protein as a whole; notably, the relevance of the CD-D region in regulating the transition between hexa- and penta-coordinated states in globins has been previously reported [13] , [15] . In the case of D. mawsoni (and C. aceratus ) Cygbs-1, the CD-loop and D-helix host five Glu residues, whereas in human CYGB two of these residues are mutated (to Asp and Ile, respectively).…”