The oxygen-binding properties of hemocyanin from the mollusk Concholepas concholepas

A comprehensive review on hemocyanin from marine products: Structure, functions, its implications for the food industry and beyond

Hemocyanin, an oxygen-transport protein, is widely distributed in the hemolymph of marine arthropods and mollusks, playing an important role in their physiological processes. Recently, hemocyanin has been recognized as a multifunctional glycoprotein involved in the immunological responses of aquatic invertebrates. Consequently, the link between hemocyanin functions and their potential applications has garnered increased attention. This review offers an integrated overview of hemocyanin's structure, physicochemical characteristics, and bioactivities to further promote the utilization of hemocyanin derived from marine products. Specifically, we review its implication in two aspects of food and aquaculture industries: quality and health. Hemocyanin's inducible phenoloxidase activity is thought to be an inducer of melanosis in crustaceans. New anti-melanosis agents targeted to hemocyanin need to be explored. The red-color change observed in shrimp shells is related to hemocyanin, affecting consumer preferences. Hemocyanin's adaptive modification in response to the aquatic environment is available as a biomarker. Additionally, hemocyanin is endowed with bioactivities encompassing anti-microbial, antiviral, and therapeutic activities. Hemocyanin is also a novel allergen and its allergenic features remain incompletely characterized.

Assessment of the In Vitro and In Vivo Antitumor Activity of Hemocyanins from Helix aspersa, Helix lucorum, and Rapana venosa in a Graffi Myeloid Tumor Model

Hemocyanins are oxygen-transporting glycoproteins in the hemolymph of some invertebrate species that attracted scientific interest as potential anticancer agents. The present study aims to assess the in vitro and in vivo anticancer activity of hemocyanins isolated from Helix aspersa, Helix lucorum, and Rapana venosa in the Graffi myeloid tumor model. The in vitro antitumor activity of the hemocyanins was determined by a MTT test and cytomorphological analysis by fluorescent and transmission electron microscopy. The in vivo effects of the hemocyanins were examined in hamsters transplanted with Graffi tumor. The serum antibody titers against the tested hemocyanins and tumor antigen were determined by ELISA. Histopathological assessment of the morphological features related to antitumor effect, immune system response, and toxicity in some internal organs was performed. The results of in vitro studies indicated that the tested hemocyanins induced significant antiproliferative and apoptogenic effects. The in vivo investigations demonstrated a protective antitumor effect, expressed in reduced transplantability, suppression of tumor growth and metastasis, reduced mortality, prolonged survival time, and absence of toxic side effects. The present study indicated that the antitumor activity of the studied hemocyanins was due to both immune stimulation and direct effects on the tumor cells, and they displayed their potential as therapeutic agents against hematological malignances.

Structure-Function Relationships of Oxygen Transport Proteins in Marine Invertebrates Enduring Higher Temperatures and Deoxygenation

AbstractPredictions for climate change-to lesser and greater extents-reveal a common scenario in which marine waters are characterized by a deadly trio of stressors: higher temperatures, lower oxygen levels, and acidification. Ectothermic taxa that inhabit coastal waters, such as shellfish, are vulnerable to rapid and prolonged environmental disturbances, such as heatwaves, pollution-induced eutrophication, and dysoxia. Oxygen transport capacity of the hemolymph (blood equivalent) is considered the proximal driver of thermotolerance and respiration in many invertebrates. Moreover, maintaining homeostasis under environmental duress is inextricably linked to the activities of the hemolymph-based oxygen transport or binding proteins. Several protein groups fulfill this role in marine invertebrates: copper-based extracellular hemocyanins, iron-based intracellular hemoglobins and hemerythrins, and giant extracellular hemoglobins. In this brief text, we revisit the distribution and multifunctional properties of oxygen transport proteins, notably hemocyanins, in the context of climate change, and the consequent physiological reprogramming of marine invertebrates.

The Evolution of Hemocyanin Genes in Caenogastropoda: Gene Duplications and Intron Accumulation in Highly Diverse Gastropods

Hemocyanin is the oxygen transport protein of most molluscs and represents an important physiological factor that has to be well-adapted to their environments because of the strong influences of abiotic factors on its oxygen affinity. Multiple independent gene duplications and intron gains have been reported for hemocyanin genes of Tectipleura (Heterobranchia) and the caenogastropod species Pomacea canaliculata, which contrast with the uniform gene architectures of hemocyanins in Vetigastropoda. The goal of this study was to analyze hemocyanin gene evolution within the diverse group of Caenogastropoda in more detail. Our findings reveal multiple gene duplications and intron gains and imply that these represent general features of Apogastropoda hemocyanins. Whereas hemocyanin exon–intron structures are identical within different Tectipleura lineages, they differ strongly within Caenogastropoda among phylogenetic groups as well as between paralogous hemocyanin genes of the same species. Thus, intron accumulation took place more gradually within Caenogastropoda but finally led to a similar consequence, namely, a multitude of introns. Since both phenomena occurred independently within Heterobranchia and Caenogastropoda, the results support the hypothesis that introns may contribute to adaptive radiation by offering new opportunities for genetic variability (multiple paralogs that may evolve differently) and regulation (multiple introns). Our study indicates that adaptation of hemocyanin genes may be one of several factors that contributed to the evolution of the large diversity of Apogastropoda. While questions remain, this hypothesis is presented as a starting point for the further study of hemocyanin genes and possible correlations between hemocyanin diversity and adaptive radiation.

The sterol regulatory element binding protein homolog of Penaeus vannamei modulates fatty acid metabolism and immune response

The sterol regulatory element binding proteins (SREBPs) transcription factors family, which regulate the expression of genes involved in cellular lipid metabolism and homeostasis, have recently been implicated in various physiological and pathophysiological processes such as immune regulation and inflammation in vertebrates. Consistent with other invertebrates, we identified a single SREBP ortholog in Penaeus vannamei (designated PvSREBP) with transcripts ubiquitously expressed in tissues and induced by lipopolysaccharide (LPS), Vibrio parahaemolyticus and Streptococcus iniae. In vivo RNA interference (RNAi) of PvSREBP attenuated the expression of several fatty acid metabolism-related genes (i.e., cyclooxygenase (PvCOX), lipoxygenase (PvLOX), fatty acid binding protein (PvFABP) and fatty acid synthase (PvFASN)), which consequently decreased the levels of total polyunsaturated fatty acids (ΣPUFAs). In addition, PvSREBP silencing decreased transcript levels of several immune-related genes such as hemocyanin (PvHMC) and trypsin (PvTrypsin), as well as genes encoding for heat-shock proteins (i.e., PvHSP60, PvHSP70 and PvHSP90). Moreover, in silico analysis revealed the presence of SREBP binding motifs on the promoters of most of the dysregulated genes, while shrimp depleted of PvSREBP were more susceptible to V. parahaemolyticus infection. Collectively, we demonstrated the involvement of shrimp SREBP in fatty acids metabolism and immune response, and propose that PvSREBP and PvHMC modulate each other through a feedback mechanism to establish homeostasis. The current study is the first to show the dual role of SREBP in fatty acid metabolism and immune response in invertebrates and crustaceans.

Molluscan Hemocyanins

Instead of the red blood of vertebrates, most molluscs have blue hemolymph containing hemocyanin, a type-3 copper-containing protein. The hemoglobin of vertebrate blood is replaced in most molluscs with hemocyanin, which plays the role of an  oxygen transporter. Oxygen-binding in hemocyanin changes its hue from colorless deoxygenated hemocyanin into blue oxygenated hemocyanin. Molecules of molluscan hemocyanin are huge, cylindrical multimeric proteins-one of the largest protein molecules in the natural world. Their huge molecular weight (from 3.3 MDa to more than 10 MDa) are the defining characteristic of molluscan hemocyanin, a property that has complicated structural analysis of the molecules for a long time. Recently, the structural analysis of a cephalopod (squid) hemocyanin has succeeded using a hybrid method employing both X-ray crystallography and cryo-EM. In a biochemical breakthrough for molluscan hemocyanin, the first quaternary structure with atomic resolution is on the verge of solving the mystery of molluscan hemocyanin. Here we describe the latest information about the molecular structure, classification and evolution of the molecule, and the physiology of molluscan hemocyanin.

Antioxidant enzymes as biomarkers of Cu and Pb exposure in the ground spiders Lycosa terrestris and Pardosa birmanica

Heavy metal exposure induces oxidative stress in terrestrial organisms, which they counteract via activation of antioxidant biomarkers. The present study investigated the effects of copper (Cu) and lead (Pb) on the total antioxidant capacity (TAC) and antioxidant enzymes such as Catalase (CAT), Glutathione reductase (GR), Superoxide dismutase (SOD) and Glutathione peroxidase (GPX) in two spider species, namely Lycosa terrestris and Pardosa birmanica. The spiders were exposed to Cu and Pb separately (10 ppm) or in combination (10 ppm each) via two different exposure routes (i.e. food and soil) for 10, 20 and 40 days. The results showed that metal accumulation and antioxidant biomarker responses in spiders were metal- and species-dependent. Also, the levels of all antioxidant biomarkers increased significantly with increasing exposure time and metal load in the bodies of spiders via both exposure routes. The significant inhibition of TAC and antioxidant enzyme activities was only observed in single Pb treatment through soil exposure. In L. terrestris, the activities of detoxification enzymes and TAC were significantly enhanced on single Cu exposure than Pb via both exposure routes. However, in P. birmanica consistent variation among antioxidant parameters were observed depending on the metal load and exposure routes. The combined metal exposure caused more pronounced increase in the level of antioxidants compared to single metal exposure in both species, mainly via food exposure. These results suggest that the antioxidant enzymes and TAC are sensitive to single and combined metal exposure via both uptake routes. These data show that antioxidant parameters can be used potential biomarkers of oxidative stress associated with metal exposure and for monitoring environmental health using spiders as bioindicators.

Broad-spectrum Antimicrobial Activity of Purified Hemocyanin Subunit IIIA Isolated from Asian Horseshoe Crab, Tachypleus gigas

BACKGROUND AND OBJECTIVES

Hemocyanin Subunit IIIA is believed to possess antimicrobial properties, but its efficacy against microbial pathogens is still unclarified. Thus, this study aimed to determine antimicrobial activities of hemocyanin subunit IIIA and to identify the best activator of this protein.

MATERIALS AND METHODS

The hemocyanin was partially purified using spin column affinity, its fraction was applied to Hi-Prep Sephacryl Exclusion 26/60 2-200 HR column, followed by Hi-Prep 26/10 Desalting Column on fast protein liquid chromatography. The purity of hemocyanin was validated by Matrix Assisted Laser Desorption Ionization-Time of Flight/Mass Spectrometry. The antimicrobial activity was performed by Disc Diffusion Test.

RESULTS

Purified hemocyanin subunit IIIA was identified to have a molecular weight of 72.9 kDa. SDS was found to be the best activator of hemocyanin, as indicated by elevated level of phenoloxidase. As for antimicrobial activity, hemocyanin was minimally inhibited by all bacteria strains tested (Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae), with relatively lower Minimum Inhibitory Concentration (MIC) at 0.005 g mL-1, than recorded MIC for fungal test strains. Two fungal strains (Penicillium sp. and A. niger) show susceptible response to phenoloxidase using MgSO4 as inducer. Whereas, lysate-treated CaCl2 induced susceptibility only to A. niger.

CONCLUSION

Hemocyanin shows better antimicrobial activity than phenoloxidase because of its broad-spectrum activity against bacterial and fungal strains tested. Hence, the hemocyanin may potentially become a new antimicrobial candidate to be discovered for a future use in treatment of resistant bacteria.