Limulus polyphemus, hemocyanin

Figure 1 Oxy (a) and deoxy (b) states of the active sites of subunit II of Limulus polyphemus hemocyanin. The three histidines coordinating Cu-A are colored red, those coordinating Cu-B green. The two copper atoms are colored blue and oxygen red. Yellow lines connect the four histidines forming the plane on which the coppers and the dioxygen are often discussed to be placed. Two axial histidines are perpendicularly oriented to this plane His204 coordinates the Cu-A site, His328 the Cu-B site. The channel to the surface for substrates to the active sites is located on the top of the active sites...

Fig. 28. Model of a subunit II-hexamer of Limulus polyphemus hemocyanin. The domains 1, 2, and 3 of each subunit are represented in black, light gray and dark gray respectively. From Hazes et al. 1993 [37] with permission...

Brouwer M, Bonaventura C, Bonaventura J (1982) Chloride and pH dependence of cooperative interactions in Limulus polyphemus hemocyanin. In Bonaventura J, Bonaventura C, Tesh S (eds) Physiology and biology of horseshoe crabs studies on normal and environmentally stressed animals. Alan R Liss, New York, p 231... 

Liu, S. and Magnus, KA. (2002) Preliminary crystallographic studies of Limulus polyphemus hemocyanin subunits Ilia, Illb and IV. Biochim. Biophys. Acta, 15%, 177-181. 

Maddaluno, J. and Fault, K.F. (1999) Mass spectrometric characterization of Limulus polyphemus hemocyanin. Biochem. Biophys. Res. Common.. 264,883-890. 

Both cations play a stabilizing role in various biological structures. Calcium ions are necessary to link the 24-subunit aggregates of the dioxygen carrier hemocyanin of Limulus polyphemus into the native 48-subunit molecule.121 The divalent character of Ca2+ probably allows it to crosslink... 

The hemocyanin subunits from Limulus polyphemus are also subdivided into three domains, which consist of the amino acids 1-154 (domain 1), 155-380 (domain 2), and 381-628 (domain 3) (Fig. 29). Domains 1 and 2 are primarily a-helical, whereas domain 3 consists mainly of /(-strands. Domain 2 is situated between the other two domains and contains the copper center. Each copper is coordinated by three histidine residues, which come from two helices. Subunit 2 is primarily responsible for the contact between the hexamer subunits. The chloride-binding site is situated between domains 1 and 2, and the calcium-bin-ding site is located in domain 3, which has a seven-ribbon /(-meander structure [37],... 

Hemocyanins are large, multisubunit dioxygen transporting proteins found in the hemolymph of many invertebrate species of the phyla of molluscs and arthropods 14). The subunits of molluscan hemocyanins contain functional units with a molecular weight of about 50,000 Da, each of which contains a dioxygen binding dicopper center. Arthropodal hemocyanins occur as hexamers, or multihexamers of subunits with a molecular weight of about 75,000 Da. As shown by the comparison of various X-ray crystal structures of the proteins from Panulirus interruptus (IS), Limulus polyphemus... 

In the arthropods hemocyanin is the respiratory pigment in the blood of all decapod crustaceans and of Limulus polyphemus (Xiphosura). It is also present in some arachnomorpha (Svedberg and Hedenius, 1933, 1934 Woods et al., 1958). 

Figure 5 Comparison of the tertiary structures of a catecholoxidase from a sweet potato Ipomea sp. (a), functional units of molluscau hemocyauins (O. dofleini (b) and R. thomasiana (c)) and arthropod hemocyanin subunits from L. polyphemus (d) and P. interruptm (e). All structures are centered with respect to domain 11 (red) carrying the active site, domain 1 is colored green, domain 111 blue. The histidines are colored gray. In the Limulus structure (d) the alpha 1,3 helix is missing compared to the Panulirus (e) structure (ellipse)...

---