Antarctic fish versus human cytoglobins – The same but yet so different

Abstract

The cytoglobins of the Antarctic fish Chaenocephalus aceratus and Dissostichus mawsoni have many features in common with human cytoglobin. These cytoglobins are heme proteins in which the ferric and ferrous forms have a characteristic hexacoordination of the heme iron, i.e. axial ligation of two endogenous histidine residues, as confirmed by electron paramagnetic resonance, resonance Raman and optical absorption spectroscopy. The combined spectroscopic analysis revealed only small variations in the heme-pocket structure, in line with the small variations observed for the redox potential. Nevertheless, some striking differences were also discovered. Resonance Raman spectroscopy showed that the stabilization of an exogenous heme ligand, such as CO, occurs differently in human cytoglobin in comparison with Antarctic fish cytoglobins. Furthermore, while it has been extensively reported that human cytoglobin is essentially monomeric and can form an intramolecular disulfide bridge that can influence the ligand binding kinetics, 3D modeling of the Antarctic fish cytoglobins indicates that the cysteine residues are too far apart to form such an intramolecular bridge. Moreover, gel filtration and mass spectrometry reveal the occurrence of non-covalent multimers (up to pentamers) in the Antarctic fish cytoglobins that are formed at low concentrations. Stabilization of these oligomers by disulfide-bridge formation is possible, but not essential. If intermolecular disulfide bridges are formed, they influence the heme-pocket structure, as is shown by EPR measurements.

Antarctic blackfin icefish genome reveals adaptations to extreme environments

“…11). In contrast, intact genes for myoglobin 47 , cytoglobin 48 and neuroglobin 49 appear in the C. aceratus genome in the context of conserved synteny among teleosts ( Supplementary Fig. 12).…”

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

“…Cygb-1 mRNA was recently also detected in some Antarctic notothenioid fish species: in the retina and liver of Dissostichus mawsoni , in the brain and liver of Chaenocephalus aceratus [24] , in the muscle of Chionodraco hamatus [21] and in the retina, brain and gills of Trematomus bernacchii and C. hamatus (D. Giordano, personal communication). The Cygb-2 gene was annotated in the genome sequence of the red-blooded Antarctic fish Notothenia coriiceps ( http://www.ncbi.nlm.nih.gov/nuccore/XM_010778246.1 ), and transcripts of Cygb-2 were also found in the brain, retina and gills of T. bernacchii and C. hamatus .…”

“…Six species, including C. aceratus , also lack Mb in skeletal muscle and heart [75] . Although the evolutionary pressure is against the maintenance of O 2 -binding proteins, they have retained Ngb [18] and Cygbs [24] , thus suggesting that selective pressure kept alive the expression of proteins involved in NO detoxification in NO-active tissues.…”

“…Cygb-1 cDNAs of the red-blooded fish D. mawsoni (family Notothenidae) and of the related icefish C. aceratus (family Channichthyidae), which lacks both Mb and Hb, were cloned from retina and brain, respectively, over-expressed and characterized by Electron Paramagnetic Resonance, Resonance Raman and optical absorption spectroscopy [24] . The two Antarctic fish Cygbs-1 are composed of 179 amino acids, with mutual sequence identity of 98%.…”

A tale of two genes: divergent evolutionary fate of haptoglobin and hemopexin in hemoglobinless antarctic icefishes

“…Although Hb would be the largest reservoir of heme, in its absence in icefishes, demands for Hx function could arise from a variety of other cellular client hemoproteins. These include cytochromes of the respiratory chain in mitochondria, which occur at greatly increased density in icefish cells than in the red-blooded species to facilitate cellular O 2 transport, heart Mb in icefish species that synthesize it (O'Brien and Mueller, 2010), microsomal and mitochondrial cytochrome P450s, as well as neuroglobin (Cheng, et al, 2009) and cytoglobin (Cuypers, et al, 2017). This level of Stop codon Polyadenylation signal client demand appears sufficient to maintain steady levels of Hx transcription.…”