RESUMO
There are three broad groups of oxygen-transport proteins found in the haemolymph (blood) of invertebrates, namely the hemocyanins, the hemerythrins and the globins. Both hemerythrins and extracellular globins are iron-based proteins that are understudied when compared to the copper-containing hemocyanins. Recent evidence suggests that hemerythrins and (giant) extracellular globins (and their linker chains) are more widely distributed than previously thought and may have biological functions beyond oxygen transport and storage. Herein, we review contemporary literature of these often-neglected proteins with respect to their structural configurations on formation and ancestral states.
Assuntos
Evolução Molecular , Globinas/química , Hemeritrina/química , Hemocianinas/química , Invertebrados/química , AnimaisRESUMO
Rhinodrilus alatus is an annelid and its giant extracellular hemoglobin (HbRa) has a molecular mass (MM) of 3500kDa. In the current study, the characterization of MM values of the HbRa subunits, and the effects of surfactants and alkaline pH upon HbRa stability were monitored. Electrophoresis, MALDI-TOF-MS and AUC show that the MM values of HbRa subunits are very close, but not identical to the Glossoscolex paulistus hemoglobin (HbGp). The monomer d is found to exist in, at least, two isoforms: the main one, d1, displays a MM of 16,166±16Da, and the second one, d2, is less intense with MM of 16,490±20Da. For the trimer abc and tetramer abcd, single contributions around 51,470Da and 67,690Da were observed, respectively. Finally, the monomers a, b, and c, present MM values of 17,133, 17,290 and 15,506Da, respectively. Both CTAC and DTAB interact strongly with HbRa, and up to seven surfactant molecules are bound to the protein. On the other hand, spectroscopic studies show that HbRa is more stable at alkaline pH, as compared to HbGp. Thus, our data suggest that alkaline medium, up to pH10.0, induces the oligomeric dissociation, without promoting the subunits unfolding and heme iron oxidation. Our results suggest that the MM of the annelid hemoglobin subunits is conserved to a great extent in the evolution process of these species.