Hemocyanin-derived phenoloxidase activity: a contributing factor to hyperpigmentation in Nephrops norvegicus

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.

The evolutionary adaptation of shrimp hemocyanin subtypes and the consequences on their structure and functions

Hemocyanin is the main respiratory protein of arthropods and is formed by hexameric and/or oligomeric subunits. Due to changes in the living environment and gene rearrangement, various hemocyanin subtypes and subunits evolved in crustaceans. This paper reviews the various hemocyanin subtypes and isoforms in shrimp and analyses published genomic data of sixteen hemocyanin family genes from Litopenaeus vannamei to explore the evolution of hemocyanin genes, subunits, and protein structure. Analysis of hemocyanin subtypes distribution and structure in various tissues was also performed and related to multiple and tissue-specific functions, i.e., immunological activity, immune signaling, phenoloxidase activity, modulation of microbiota homeostasis, and energy metabolism. The functional diversity of shrimp hemocyanin due to molecular polymorphism, transcriptional regulation, alternative splicing, degradation into functional peptides, interaction with other proteins or genes, and structural differences will also be highlighted for future research. Inferences would be drawn from other crustaceans to explain how evolution has changed the structure-function of hemocyanin and its implication for evolutionary research into the multifunctionality of hemocyanin and other related proteins in shrimp.

Exploring the Antimicrobial Potential and Biofilm Inhibitory Properties of Hemocyanin from Hemifusus pugilinus (Born, 1778)

The seafood industry plays a huge role in the blue economy, exploiting the advantage of the enriched protein content of marine organisms such as shrimps and molluscs, which are cultured in aquafarms. Diseases greatly affect these aquatic organisms in culture and, hence, there is need to study, in detail, their innate immune mechanisms. Hemocyanin is a non-specific innate defense molecule present in the blood cells of several invertebrates, especially molluscs, arthropods, and annelids. It is concerned with oxygen transport, blood clotting, and immune enhancement. In the present study, this macromolecular metalloprotein was isolated from the hemolymph of the marine snail Hemifusus pugilinus (Born, 1778) using Sephadex G-100 gel filtration column chromatography. It occurred as a single band (MW 80 kDa) on SDS-PAGE. High-performance liquid chromatography (HPLC) of the purified hemocyanin showed a single peak with a retention time of 4.3 min. The secondary structure and stability of the protein were detected using circular dichroism (CD), and the spectra demonstrated negative ellipticity bands close to 208 nm and 225 nm, indicating β-sheets. Further exploration of the purified hemocyanin revealed remarkable antimicrobial and antibiofilm activities against Gram-positive (Enterococcus faecalis and Staphylococcus aureus) and Gram-negative bacteria (Pseudomonas aeruginosa and Proteus vulgaris) at a concentration of 1-5 μg/mL. Spectrophotometric and in situ microscopic analyses (CLSM) unveiled the potential of the purified hemocyanin to inhibit biofilm formation in these bacteria with a minimal inhibitory concentration of 40 μg/mL. Furthermore, H. pugilinus hemocyanin (10 μg/mL concentration) displayed antifungal activity against Aspergillus niger. The purified hemocyanin was also assessed for cytotoxicity against human cancer cells using cell viability assays. Altogether, the present study shows that molluscan hemocyanin is a potential antimicrobial, antibiofilm, antifungal, anticancer, and immunomodulatory agent, with great scope for application in the enhancement of the immune system of molluscs, thereby facilitating their aquaculture.

The transcription factor CSL homolog in Penaeus vannamei positively regulates the transcription of the hemocyanin small subunit gene

Hemocyanin, a copper-containing respiratory protein, is abundantly present in hemolymph of arthropods and mollusks and performs a variety of immunological functions. However, the regulatory mechanisms of hemocyanin gene transcription remain largely unclear. Our previous work showed that knockdown of the transcription factor CSL, a component of the Notch signaling pathway, downregulated the expression of Penaeus vannamei hemocyanin small subunit gene (PvHMCs), indicating the involvement of CSL in regulating the PvHMCs transcription. In this study, we identified a CSL binding motif ("GAATCCCAGA", +1675/+1684 bp) in the core promoter of PvHMCs (designated as HsP3). Dual luciferase reporter assay and electrophoretic mobility shift assay (EMSA) demonstrated that the CSL homolog in P. vannamei (PvCSL) could directly bind and activate the HsP3 promoter. Moreover, in vivo silencing of PvCSL significantly attenuated the mRNA and protein expression of PvHMCs. Finally, in response to Vibrio parahaemolyticus, Streptococcus iniae and white spot syndrome virus (WSSV) challenge, the transcript of PvCSL and PvHMCs showed a positive correlation, suggesting that PvCSL could also modulate the expression of PvHMCs upon pathogen stimulation. Taken together, our present finding is the first to demonstrate that PvCSL is a crucial factor in transcriptional control of PvHMCs.

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.

Inter-Subunit Dynamics Controls Tunnel Formation During the Oxygenation Process in Hemocyanin Hexamers

Hemocyanin from horseshoe crab in its active form is a homo-hexameric protein. It exists in open and closed conformations when transitioning between deoxygenated and oxygenated states. Here, we present a detailed dynamic atomistic investigation of the oxygenated and deoxygenated states of the hexameric hemocyanin using explicit solvent molecular dynamics simulations. We focus on the variation in solvent cavities and the formation of tunnels in the two conformational states. By employing principal component analysis and CVAE-based deep learning, we are able to differentiate between the dynamics of the deoxy- and oxygenated states of hemocyanin. Finally, our results identify the deoxygenated open conformation, which adopts a stable, closed conformation after the oxygenation process.

Comparative characterization of the hemocyanin-derived phenol oxidase activity from spiders inhabiting different thermal habitats

Enzymes adapted to cold temperatures are commonly characterized for having higher Michaelis-Menten constants (K_M) values and lower optimum and denaturation temperature, when compared to other meso or thermophilic enzymes. Phenoloxidase (PO) enzymes are ubiquitous in nature, however, they have not been reported in spiders. It is the oxygen carrier protein hemocyanin (Hc), found at high concentrations in their hemolymph, which displays an inducible PO activity. Hence, we hypothesize that Hc-derived PO activity could show features of cold adaptation in alpine species. We analyzed the Hc from two species of Theraphosidae from different thermal environments: Euathlus condorito (2400 m a.s.l.) and Grammostola rosea (500 m a.s.l.). Hc was purified from the hemolymph of both spiders and was characterized by identifying subunit composition and measuring the sodium dodecyl sulfate (SDS)-induced PO activity. The high-altitude spider Hc showed higher PO activity under all conditions and higher apparent Michaelis-Menten constant. Moreover, the optimum temperature for PO activity was lower for E. condorito Hc. These findings suggest a potential adaptation at the level of Hc-derived PO activity in Euathlus condorito, giving insights on possible mechanisms used by this mygalomorph spider to occupy extremes and variable thermal environments.

Hemocyanin of the caenogastropod Pomacea canaliculata exhibits evolutionary differences among gastropod clades

Structural knowledge of gastropod hemocyanins is scarce. To better understand their evolution and diversity we studied the hemocyanin of a caenogastropod, Pomacea canaliculata (PcH). Through a proteomic and genomic approach, we identified 4 PcH subunit isoforms, in contrast with other gastropods that usually have 2 or 3. Each isoform has the typical Keyhole limpet-type hemocyanin architecture, comprising a string of eight globular functional units (FUs). Correspondingly, genes are organized in eight FUs coding regions. All FUs in the 4 genes are encoded by more than one exon, a feature not found in non- caenogastropods. Transmission electron microscopy images of PcH showed a cylindrical structure organized in di, tri and tetra-decamers with an internal collar structure, being the di and tri-decameric cylinders the most abundant ones. PcH is N-glycosylated with high mannose and hybrid-type structures, and complex-type N-linked glycans, with absence of sialic acid. Terminal β-N-GlcNAc residues and nonreducing terminal α-GalNAc are also present. The molecule lacks O-linked glycosylation but presents the T-antigen (Gal-β1,3-GalNAc). Using an anti-PcH polyclonal antibody, no cross-immunoreactivity was observed against other gastropod hemocyanins, highlighting the presence of clade-specific structural differences among gastropod hemocyanins. This is, to the best of our knowledge, the first gene structure study of a Caenogastropoda hemocyanin.

Multifunctional Roles of Hemocyanins

The copper-containing hemocyanins are proteins responsible for the binding, transportation and storage of dioxygen within the blood (hemolymph) of many invertebrates. Several additional functions have been attributed to both arthropod and molluscan hemocyanins, including (but not limited to) enzymatic activity (namely phenoloxidase), hormone transport, homeostasis (ecdysis) and hemostasis (clot formation). An important secondary function of hemocyanin involves aspects of innate immunity-such as acting as a precursor of broad-spectrum antimicrobial peptides and microbial/viral agglutination. In this chapter, we present the reader with an up-to-date synthesis of the known functions of hemocyanins and the structural features that facilitate such activities.

Structural and conformational stability of hemocyanin from the garden snail Cornu aspersum

Various aspects of biomedical applications of molluscan hemocyanins, associated with their immunogenic properties and antitumor activity, promoted us to perform structural studies on these glycoproteins. The stability and reassociation behavior of native Cornu aspersum hemocyanin (CaH) are studied in the presence of different concentrations of Ca2+ and Mg2+ ions and pH values using electron microscopy. Higher concentrations of those ions led to a more rapid reassociation of CaH, resulting in stable multidecamers with different lengths. The conformational changes of native CaH are investigated within a wide pH-temperature range by UV circular dichroism. The relatively small changes of initial [θ]λ indicated that many secondary structural elements are preserved, even at high temperatures above 80°C, especially at neutral pH. The mechanism of thermal unfolding of CaH has a complicated character, and the process is irreversible. The conformational stability of the native didecameric aggregates of CaH toward various denaturants indicates that hydrophilic and polar forces stabilize the quaternary structure. For the first time, the unfolding of native CaH in water solutions in the presence of four different denaturants is investigated. The free energy of stabilization in water, ∆GD H2O, was calculated in the range of 15.48–16.95 kJ mol−1. The presented results will facilitate the further investigation of the properties and potential applications of CaH.

Inhibitory effects of compounds isolated from Lepechinia meyenii on tyrosinase

To contribute enzymatic browning inhibitors to the food industry and also extend knowledge about the phytochemical profile of the anti-tyrosinase plant Lepechinia meyenii, its ethanol extract was subjected to bioguided fractionation. Three hydroxycinnamic acids, p-coumaric acid (1), caffeic acid (2) and rosmarinic acid (3), were isolated as mainly responsible for its activity. Compounds 1, 2 and 3 showed themselves highly effective for inhibiting tyrosinase with IC₅₀ values of 0.30, 1.50 and 4.14 μM, respectively, for monophenolase activity and 0.62, 2.30 and 8.59 μM, respectively for diphenolase activity. This is the first report describing the isolation of the compounds causing the tyrosinase inhibitory activity of L. meyenii extract. The inhibitory kinetics of 1-3 using both L-tyrosine and L-DOPA as substrates was investigated and the results obtained were discussed at molecular level by docking analysis. The resulting compounds 1-3 and a phenolic-enriched fraction of the extract, 2.9-fold more active than the starting material, may be suitable as non-toxic and inexpensive alternatives for the control of deleterious enzymatic darkening.

Hydration facilitates oxygenation of hemocyanin: perspectives from molecular dynamics simulations

Molecular dynamics simulations were applied to deoxy- and oxy-hemocyanins using newly developed force field parameters for the dicopper site to evaluate their structural and dynamical properties. Data obtained from the simulations provided information of the oxygenation effect on the active site and overall topology of the protein that was analyzed by root-mean-square deviations, b-factors, and dicopper coordination geometries. Domain I of the protein was found to demonstrate higher flexibility with respect to domain II because of the interfacial rotation between domain I and II that was further endorsed by computing correlative domain movements for both forms of the protein. The oxygenation effect on the overall structure of the protein or polypeptide subunit was further explored via gyration radii evaluated for the metal-binding domain and for the whole subunit. The evaluation of hydration dynamics was carried out to understand the water mediated role of amino acid residues of the solvent tunnel facilitating the entry of oxygen molecule to the dicopper site of hemocyanin.

Immunological properties of oxygen-transport proteins: hemoglobin, hemocyanin and hemerythrin

It is now well documented that peptides with enhanced or alternative functionality (termed cryptides) can be liberated from larger, and sometimes inactive, proteins. A primary example of this phenomenon is the oxygen-transport protein hemoglobin. Aside from respiration, hemoglobin and hemoglobin-derived peptides have been associated with immune modulation, hematopoiesis, signal transduction and microbicidal activities in metazoans. Likewise, the functional equivalents to hemoglobin in invertebrates, namely hemocyanin and hemerythrin, act as potent immune effectors under certain physiological conditions. The purpose of this review is to evaluate the true extent of oxygen-transport protein dynamics in innate immunity, and to impress upon the reader the multi-functionality of these ancient proteins on the basis of their structures. In this context, erythrocyte-pathogen antibiosis and the immune competences of various erythroid cells are compared across diverse taxa.

Comparative studies of hemolymph physiology response and HIF-1 expression in different strains of Litopenaeus vannamei under acute hypoxia

Litopenaeus vannamei has a high commercial value and is the primary cultured shellfish species globally. In this study, we have compared the hemolymph physiological responses between two L. vannamei strains under acute hypoxia. The results showed that hemocyanin concentration (HC) of strain A6410 was significantly higher than strain Zhengda; Total hemocyte counts (THC) decreased significantly in both strains under hypoxic stress (p < 0.05). We also investigated the temporal and spatial variations of hypoxia inducible factors 1 (HIF-1) by qRT-PCR. The results showed that hypoxia for 12 h increased the expression levels of HIF-1α in tissues of muscle and gill from the two strains (p < 0.05). In the hepatopancreas, the expression levels of HIF-1 increased significantly in strain Zhengda and decreased significantly in strain A6410 (p < 0.05). No significant changes of HIF-1 expression were detected in the same tissues between the two strains under hypoxia for 6 h (p > 0.05), but in the gills and hepatopancreas under hypoxia for 12 h (p < 0.05). Additionally, the expression level of HIF-1 was higher in the strain Zhengda than A6410 in the same tissue under hypoxia for 12 h. It was indicated that the hypoxic tolerance of Litopenaeus vannamei was closely correlated with the expression level of HIF-1, and the higher expression level of HIF-1 to hypoxia, the lower tolerance to hypoxia in the early stage of hypoxia. These results can help to better understand the molecular mechanisms of hypoxic tolerance and speed up the selective breeding process of hypoxia tolerance in L. vannamei.

Melanosis in Penaeus monodon: Involvement of the Laccase-like Activity of Hemocyanin

In shrimp, the development of postmortem melanosis resulting from phenoloxidase activities leads to important economic losses. Phenoloxidase enzymes include catechol oxidases, laccases, and tyrosinases, but hemocyanin is also capable of phenoloxidase activities. These activities have been explored in Penaeus monodon, using different substrates. Results highlighted that tyrosinase-specific substrates were little oxidized, whereas hydroquinone (laccase-specific substrate) was more highly oxidized than l-DOPA (nonspecific substrate) in the pereopods and pleopods. Global phenoloxidase activity, assayed with l-DOPA, did not appear thermally stable over time and probably resulted from phenoloxidase enzymes. Conversely, the laccase-like activity assayed with hydroquinone was thermally stable over time, reflecting the thermal stability of hemocyanin. Independently of the anatomical compartment, the temperature, or the substrate, the highest activities were assayed in the cuticular compartments. This study demonstrates the complexity of phenoloxidase activities in P. monodon, and the importance of considering all the activities, including laccase-like activities such as that of hemocyanin.

Design, synthesis, and anti-melanogenic effects of (E)-2-benzoyl-3-(substituted phenyl)acrylonitriles

Background

Tyrosinase is the most prominent target for inhibitors of hyperpigmentation because it plays a critical role in melaninogenesis. Although many tyrosinase inhibitors have been identified, from both natural and synthetic sources, there remains a considerable demand for novel tyrosinase inhibitors that are safer and more effective.

Methods

(E)-2-Benzoyl-3-(substituted phenyl)acrylonitriles (BPA analogs) with a linear β-phenyl-α,β-unsaturated carbonyl scaffold were designed and synthesized as potential tyrosinase inhibitors. We evaluated their effects on cellular tyrosinase activity and melanin biosynthesis in murine B16F10 melanoma cells and their ability to inhibit mushroom tyrosinase activity.

Results

BPA analogs exhibited inhibitory activity against mushroom tyrosinase. In particular, BPA13 significantly suppressed melanin biosynthesis and inhibited cellular tyrosinase activity in B16F10 cells in a dose-dependent manner. A docking study revealed that BPA13 had higher binding affinity for tyrosinase than kojic acid.

Conclusion

BPA13, which possesses a linear β-phenyl-α,β-unsaturated carbonyl scaffold, is a potential candidate skin-whitening agent and treatment for diseases associated with hyperpigmentation.

Characterization of phenoloxidase activity from spider Polybetes pythagoricus hemocyanin

Hemocyanin of the spider Polybetes pythagoricus, in addition to its typical role as an oxygen transporter, also exhibits a phenoloxidase activity induced by micellar concentrations of SDS. In the present work, we found the kinetic parameters Km and Vmax of Polybetes pythagoricus hemocyanin (PpHc) PO activity to be 0.407 mM and 0.081 µmolmin(-1) mg protein(-1) , respectively. Dopamine was used as the substrate with SDS at a final concentration of 10 mM and a 30-min incubation at 25°C. Conformational changes in Hc associated with the SDS treatment were analyzed using far-UV circular dichroism, intrinsic fluorescence and absorption spectroscopy. The secondary and tertiary structural changes of PpHc induced by SDS led to increases in α-helical content and tryptophan fluorescence intensity. A reduction in the absorption spectrum at 340 nm in the presence of SDS was also observed. These results suggest that the SDS-induced PO activity of PpHc can be ascribed to conformational changes in the local environment of the typer-3 copper active site.

Identification of candidate antimicrobial peptides derived from abalone hemocyanin

Hemocyanins present in invertebrate hemolymph are multifunctional proteins, responsible for oxygen transport and contributing to innate immunity through phenoloxidase-like activity. In arthropods, hemocyanin has been identified as a source of broad-spectrum antimicrobial peptides during infection. Conversely, no hemocyanin-derived antimicrobial peptides have been reported for molluscs. The present study describes a putative antimicrobial region, termed haliotisin, located within the linking sequence between the α-helical domain and β-sheet domain of abalone (Haliotis tuberculata) hemocyanin functional unit E. A series of synthetic peptides based on overlapping fragments of the haliotisin region were tested for their bactericidal potential. Incubating Gram-positive and Gram-negative bacteria in the presence of certain haliotisin peptides, notably peptides 3-4-5 (DTFDYKKFGYRYDSLELEGRSISRIDELIQQRQEKDRTFAGFLLKGFGTSAS) led to reductions in microbial growth. Furthermore, transmission electron micrographs of haliotisin-treated bacteria revealed damages to the microbial cell wall. Data discussed here provides the first evidence to suggest that molluscan hemocyanin may act as a source of anti-infective peptides.

Effect of chlorogenic acid on melanogenesis of B16 melanoma cells

Chlorogenic acid (CGA), the ester formed between caffeic acid and l-quinic acid, is a widespread phenolic compound. It is part of the human diet, found in foods such as coffee, apples, pears, etc. CGA is also was widely used in cosmetics, but the effects of CGA on melanogenesis are unknown. In this study, we analyzed the effects of CGA on cell proliferation, melanin content and tyrosinase of B16 murine melanoma cells. Additionally, the enzymatic reactions of CGA in B16 melanoma cells lytic solution were detected by UV spectrophotometry. Results showed CGA at 30 and 60 μM significantly suppresses cell proliferation. 8-MOP at 100 μM significantly promotes cell proliferation, but CGA can counter this. Incubated for 24 h, CGA (500 μM) improves melanogenesis while suppressing tyrosinase activity in B16 melanoma cells or 8-methoxypsoralen (8-MOP) co-incubated B16 melanoma cells. After 12 h, B16 melanoma cell treatment with CGA leads to an increase in melanin accumulation, however, after 48 h there is a decrease in melanin production which correlates broadly with a decrease in tyrosinase activity. CGA incubated with lytic solution 24 h turned brown at 37 °C. The formation of new products (with a maximum absorption at 295 nm) is associated with reduction of CGA (maximum absorption at 326 nm). Therefore, CGA has its two sidesroles in melanogenesis of B16 melanoma cells. CGA is a likely a substrate of melanin, but the metabolic product(s) of CGA may suppress melanogenesis in B16 melanoma cells by inhibiting tyrosinase activity.

Diverse immune functions of hemocyanins

Substantial evidence gathered recently has revealed the multiple functionalities of hemocyanin. Contrary to previous claims that this ancient protein is involved solely in oxygen transport within the hemolymph of invertebrates, hemocyanin and hemocyanin-derived peptides have been linked to key aspects of innate immunity, in particular, antiviral and phenoloxidase-like activities. Both phenoloxidase and hemocyanin belong to the family of type-3 copper proteins and share a high degree of sequence homology. While the importance of phenoloxidase in immunity and development is well characterised, the contribution of hemocyanin to biological defence systems within invertebrates is not recognised widely. This review focusses on the conversion of hemocyanin into a phenoloxidase-like enzyme and the array of hemocyanin-derived immune responses documented to date.