Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Review
. 2018 Apr;10(2):191-202.
doi: 10.1007/s12551-017-0349-4. Epub 2017 Dec 12.

Molluscan hemocyanin: structure, evolution, and physiology

Sanae Kato  1 , Takashi Matsui  2 , Christos Gatsogiannis  3 , Yoshikazu Tanaka  4   5
Affiliations
Review

Molluscan hemocyanin: structure, evolution, and physiology

Sanae Kato et al. Biophys Rev. 2018 Apr.

Abstract

Most molluscs have blue blood because their respiratory molecule is hemocyanin, a type-3 copper-binding protein that turns blue upon oxygen binding. Molluscan hemocyanins are huge cylindrical multimeric glycoproteins that are found freely dissolved in the hemolymph. With molecular masses ranging from 3.3 to 13.5 MDa, molluscan hemocyanins are among the largest known proteins. They form decamers or multi-decamers of 330- to 550-kDa subunits comprising more than seven paralogous functional units. Based on the organization of functional domains, they assemble to form decamers, di-decamers, and tri-decamers. Their structure has been investigated using a combination of single particle electron cryo-microsopy of the entire structure and high-resolution X-ray crystallography of the functional unit, although, the one exception is squid hemocyanin for which a crystal structure analysis of the entire molecule has been carried out. In this review, we explain the molecular characteristics of molluscan hemocyanin mainly from the structural viewpoint, in which the structure of the functional unit, architecture of the huge cylindrical multimer, relationship between the composition of the functional unit and entire tertiary structure, and possible functions of the carbohydrates are introduced. We also discuss the evolutionary implications and physiological significance of molluscan hemocyanin.

Keywords: Electron cryo-microscopy; Evolution; Glycoprotein; Molluscan hemocyanin; Oxygen transporter; Structure; X-ray crystallography.

PubMed Disclaimer

Conflict of interest statement

Conflict of interest

Sanae Kato declares that she has no conflicts of interest. Takashi Matsui declares that he has no conflicts of interest. Christos Gatsogiannis declares that he has no conflicts of interest. Yoshikazu Tanaka declares that he has no conflicts of interest.

Ethical approval

This article does not contain any studies with human participants by any of the authors. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.

Financial information

SK was a recipient of the JSPS KAKENHI (25450298) and Regional Innovation Strategy Support Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. YT received support from JSPS KAKENHI (24000011, and 15KK0248) and JST, PRESTO (JPMJPR1517). TM received support from JSPS KAKENHI (16K18501).

Figures

Fig. 1
Fig. 1
Structure of molluscan hemocyanin and its subunit. a–d Representative area of negatively stained transmission electron microscopy (TEM) image (left), scheme of hemocyanin subunit (bottom), and three-dimensional (3D) model of four molluscan hemocyanin types (right) are shown. a Nautilus-type hemocyanin (TEM image: Enterooctopus dofleini hemocyanin; 3D structure: nautilus hemocyanin). b Squid-type hemocyanin (TEM image: Todarodes pacificus hemocyanin; 3D structure: crystal structure of T. pacificus hemocyanin. The Cu2O2 cluster of FU-d*, one of the inner domains, is indicated as purple spheres because the precise structure of FU-d* has not been determined yet). c Keyhole limpet-type hemocyanin (TEM image: Nordotis discus hannai hemocyanin; 3D structure: electron cryo-microsopy (cryoEM) structure of keyhole limpet hemocyanin). d Mega-hemocyanin-type hemocyanin (Melanoides tuberculata hemocyanin). C C-terminus, N N-terminus. Scheme of hemocyanin subunits: a, b, c, d, e, f, g, h Functional units (FUs) of molluscan hemocyanins, f1, f2, f3, f4, f5, f6 homologous FUs
Fig. 2
Fig. 2
Structures of the functional units. a, b Ribbon diagrams of FU-g (a) and FU-h (b). d, e Dimer structure of FU-g (d) and FU-h (e) are also shown. The N-terminal core domain (N), C-terminal β-sandwich domain (C), and cupredoxin domain are shown in cyan, magenta, and orange, respectively. c Close-up views of active sites of FU-g. Coordinated residues are represented as sticks. Copper (Cu) atoms and oxygen atoms (O) are represented as spheres
Fig. 3
Fig. 3
Architecture of the wall region. Two protomers assemble into one plate-like protomer dimer with a twofold symmetry, shown as a green arrow. Five protomer dimers assemble to form a decamer with a fivefold symmetry, shown as an orange arrow, which generates D5 symmetry. Each protomer is represented by a separate color
Fig. 4
Fig. 4
Architecture of the plate-like dimer. a FUs in one plate-like dimer are highlighted in separate colors. Outline of one the protomer is highlighted. b Architecture of plate-like dimer. c–e Three types of FU dimers comprising the plate-like dimer. f–h The relative orientation of the four FUs in the top (f), middle (g), and bottom regions (h) are shown
Fig. 5
Fig. 5
Nautilus-type hemocyanin. Conformation of nautilus-type hemocyanin illustrated from lateral (a, c) and top views (b, d). a, b Wall region and FU-g are shown as gray and green surfaces, respectively. c, d Protomers A and D, which cooperatively form an inner collar domain, are shown in red and blue, respectively
Fig. 6
Fig. 6
Crystal structure of squid-type hemocyanin. Crystal structure of squid-type hemocyanin illustrated from lateral (a) and top (b) views. Wall region and FU-g are shown as gray and green ribbons, respectively. Cu2O2 cluster of FU-d* is shown as brown spheres because the precise structure of FU-d* has not yet been determined
Fig. 7
Fig. 7
Keyhole limpet-type hemocyanin. Conformation of keyhole limpet-type hemocyanin illustrated from lateral (a) and top views (b). Wall region, FU-g, and FU-h are shown as gray, green, and orange surfaces, respectively
Fig. 8
Fig. 8
Architecture of mega-hemocyanin. a–c Architecture of mega-hemocyanin viewed from lateral (a) and top (b) and as sectional view (c). d Composition of each decamer of mega-hemocyanin. Gastropod-type decamer and rhombus-shaped cylindrical core are shown. For clarity, the sectional representation of gastropod-type decamer is also shown. e Top view of rhombus-shaped cylindrical core
Fig. 9
Fig. 9
Carbohydrate. a Carbohydrate clusters. Carbohydrates are represented as cyan spheres. Each protomer is illustrated as individual colors. b Close-up view of the carbohydrate cluster. FUs and carbohydrates are indicated as ribbons and sticks, respectively. FUs are shown as color codes as shown in Fig. 4
Fig. 10
Fig. 10
Negative stain of TEM image of hemocyanin of weakened squid. Most hemocyanins dissociate to subunit-oligomers or subunits. Bar: 100 nm
See this image and copyright information in PMC

References

    1. Altenhein B, Markl J, Lieb B. Gene structure and hemocyanin isoform HtH2 from the mollusc Haliotis Tuberculata indicate early and late intron hot spots. Gene. 2002;301:53–60. doi: 10.1016/S0378-1119(02)01081-8. - DOI - PubMed
    1. Becker MI, Arancibia S, Salazar F, Campo MD, Ioannes AD. (2014) Mollusk hemocyanins as natural immunostimulants in biomedical applications. In: Duc GHT (ed) Immune response activation. InTech, Rijeka, Croatia, pp 45–72
    1. Bergmann S, Lieb B, Ruth P, Markl J. The hemocyanin from a living fossil, the cephalopod Nautilus pompilius: protein structure, gene organization, and evolution. J Mol Evol. 2006;62:362–374. doi: 10.1007/s00239-005-0160-x. - DOI - PubMed
    1. Boisset N, Mouche F. Sepia officinalis hemocyanin: a refined 3D structure from field emission gun cryoelectron microscopy. J Mol Biol. 2000;296:459–472. doi: 10.1006/jmbi.1999.3460. - DOI - PubMed
    1. Cuff ME, Miller KI, van Holde KE, Hendrickson WA. Crystal structure of a functional unit from octopus hemocyanin. J Mol Biol. 1998;278:855–870. doi: 10.1006/jmbi.1998.1647. - DOI - PubMed

LinkOut - more resources