A combination of dynamic light scattering and polarized resonance Raman scattering applied in the study of Arenicola Marina extracellular hemoglobin

Transcriptomic profiling of immune-associated molecules in the coelomocytes of lugworm Arenicola marina (Linnaeus, 1758)

Organization and functioning of immune system remain unevenly studied in different taxa of lophotrochozoan animals. We analyzed transcriptomic data on coelomocytes of the lugworm Arenicola marina (Linnaeus, 1758; Annelida, Polychaeta) to gain insights into the molecular mechanisms involved in polychaete immunity. Coelomocytes are specialized motile cells populating coelomic fluid of annelids, responsible for cellular defense reactions and providing humoral immune factors. The transcriptome was enriched with immune-related transcripts by challenging the cells in vitro with lipopolysaccharides of Escherichia coli and Zymosan from Saccharomyces cerevisiae. Our analysis revealed a multifaceted and complex internal defense system of the lugworm. A. marina possesses orthologs of proto-complement-like factors: six thioester-containing proteins, a complement-like receptor, and a MASP-related serine protease (MReM2). A. marina coelomocytes employ pattern-recognition receptors to detect pathogens and regulate immune responses. Among them, there are 18 Toll-like receptors and various putative lectin-like proteins with evolutionary conserved and taxa-specific domains. C-type lectins and a novel family of Gal-binding and CUB domains containing receptors were the most abundant in the transcriptome. The array of pore-forming proteins in the coelomocytes was surprisingly reduced compared to that of other invertebrate species. We characterized a set of conserved proteins metabolizing reactive oxygen species and nitric oxide and expanded the arsenal of potential antimicrobial peptides. Phenoloxidase activity in immune cells of lugworm is mediated only by laccase enzyme. The described repertoire of immune-associated molecules provides valuable candidates for further functional and comparative research on the immunity of annelids.

Oligomeric stability of Glossoscolex paulistus hemoglobin as a function of the storage time

Glossoscolex paulistus hemoglobin structure is composed of 144 globin chains and 36 polypeptide chains lacking the heme group, with a total molecular mass of 3600 kDa. The current study focuses on the oxy-HbGp oligomeric stability, as a function of the storage time, at pH 7.0, using dynamic light scattering, analytical ultracentrifugation (AUC), optical absorption and size exclusion chromatography (SEC). HbGp stored in Tris-HCl buffer, pH 7.0, at 4 °C, for two years remains in the native form, while 4-6 years HbGp stocks present typical hemichrome species absorption spectra. AUC and SEC analyses show that the contribution of HbGp-subunits, such as, dodecamer (abcd)₃, tetramer abcd, trimer abc and monomer d, increases with the protein aging due to the lower stability of the HbGp with the time. The dissociation and the oxidation of the iron noted for the older protein solutions indicate that HbGp storage for periods of time longer than two years changes its ability to carry oxygen. Despite the reduction of HbGp stability and oxygen carrying capacity with aging, the protein stability is still larger as compared to mammalian hemoglobins. Thus, the extracellular hemoglobins are quite stable and resistant to the auto-oxidation process, making them of interest for biotechnological applications.

Increasing the stability of Lumbricus terrestris erythrocruorin via poly(acrylic acid) conjugation

Since donated red blood cells must be constantly refrigerated, they are often unavailable in remote areas and battlefields. The goal of this study was to synthesize a highly stable blood substitute that does not require refrigeration. Specifically, the extracellular haemoglobin (a.k.a. erythrocruorin, Ec) of the earthworm Lumbricus terrestris erythrocruororin (LtEc) was cross-linked with poly(acrylic acid) (PAA) and ethylene diamine (EDA). PAGE analysis of the LtEc nanoparticles reveals cross-linking between subunits, while dynamic light scattering and scanning electron microscopy show that cross-linking significantly increases the size of the LtEc nanoparticles (164 ± 13.9 nm). Cross-linking also significantly increased the thermal stability of the LtEc nanoparticles by 10 °C (Tm = 72 ± 0.84 °C) relative to native LtEc (Tm = 62 ± 0.6 °C). In addition, while native LtEc rapidly dissociates at pH 9, the LtEc nanoparticles resist subunit dissociation up to pH 10. The oxygen affinity of the LtEc nanoparticles (P50 = 6.85 ± 0.13 mm Hg) is much higher than native LtEc (P50 = 26.67 ± 0.4 mm Hg), but the cooperativity (n = 2.43 ± 0.12) is not affected. Altogether, these results show that cross-linking LtEc with PAA and EDA provides a potential blood substitute with increased stability and oxygen affinity.

Direct comparison of oligochaete erythrocruorins as potential blood substitutes

While many blood substitutes are based on mammalian hemoglobins (e.g., human hemoglobin, HbA), the naturally extracellular hemoglobins of invertebrates (a.k.a. erythrocruorins, Ecs) are intriguing alternative oxygen carriers. Specifically, the erythrocruorin of Lumbricus terrestris has been shown to effectively deliver oxygen in mice and rats without the negative side effects observed with HbA. In this study, the properties of six oligochaete Ecs (Lumbricus terrestris, Eisenia hortensis, Eisenia fetida, Eisenia veneta, Eudrilus eugeniae, and Amynthas gracilis) were compared in vitro to identify the most promising blood substitute candidate(s). Several metrics were used to compare the Ecs, including their oxidation rates, dissociation at physiological pH, thermal stability, and oxygen transport characteristics. Overall, the Ecs of Lumbricus terrestris (LtEc) and Eisenia fetida (EfEc) were identified as promising candidates, since they demonstrated high thermal and oligomeric stability, while also exhibiting relatively low oxidation rates. Interestingly, the O₂ affinity of LtEc (P₅₀ = 26.25 mmHg at 37 °C) was also observed to be uniquely lower than EfEc and all of the other Ecs (P₅₀ = 9.29–13.62 mmHg). Subsequent alignment of the primary sequences of LtEc and EfEc revealed several significant amino acid substitutions within the D subunit interfaces that may be responsible for this significant change in O₂ affinity. Nonetheless, these results show that LtEc and EfEc are promising potential blood substitutes that are resistant to oxidation and denaturation, but additional experiments will need to be conducted to determine their safety, efficacy, and the effects of their disparate oxygen affinities in vivo.

Guanidine hydrochloride and urea effects upon thermal stability of Glossoscolex paulistus hemoglobin (HbGp)

Glossoscolex paulistus hemoglobin (HbGp) has a molecular mass of 3600kDa. It belongs to the hexagonal bilayer hemoglobin class, which consists of highly cooperative respiratory macromolecules found in mollusks and annelids. The present work focusses on oxy-HbGp thermal stability, in the presence of urea and guanidine hydrochloride (GuHCl), monitored by several techniques. Initially, dynamic light scattering data show that the presence of GuHCl induces the protein oligomeric dissociation, followed by a significant 11-fold increase in the hydrodynamic diameter (DH) values, due to the formation of protein aggregates in solution. In contrast, urea promotes the HbGp oligomeric dissociation, followed by unfolding process at high temperatures, without aggregation. Circular dichroism data show that unfolding critical temperature (Tc) of oxy-HbGp decreases from 57°C, at 0.0 mol/L of the denaturant, to 45°C, in the presence of 3.5 mol/L of urea, suggesting the reduction of HbGp oligomeric stability. Moreover, differential scanning calorimetry results show that at lower GuHCl concentrations, some thermal stabilization of the hemoglobin is observed, whereas at higher concentrations, the reduction of stability takes place. Besides, HbGp is more stable in the presence of urea when compared with the guanidine effect, as deduced from the differences in the concentration range of denaturants.