PDBsum entry 1hc4

Oxygen transport

PDB id: 1hc4

Contents

Protein chain

634 a.a.

Metals

_CU ×2

Waters ×186

References listed in PDB file

Key reference

• Title: Crystal structure of hexameric haemocyanin from panulirus interruptus refined at 3.2 a resolution.
• Authors: A.Volbeda, W.G.Hol.
• Ref.: J Mol Biol, 1989, 209, 249-279.
• PubMed id: 2585484

Abstract

The use of non-crystallographic symmetry restraints in the refinement of the haemocyanin hexamer from Panulirus interruptus at 3.2 A resolution has resulted in a final model with a very reasonable geometry and a crystallographic R-factor of 20.1%, using 59,193 observed structure factor amplitudes between 8.0 and 3.2 A. The mean co-ordinate error is approximately 0.35 A. The six subunits appear to be related by symmetry operations that differ slightly from 32 point group symmetry. The six subunits have essentially maintained the same structure. The hexamer, with point group 32, is best described as a trimer of "tight dimers". The contacts between the subunits in such a dimer are more numerous, and better conserved during evolution than contacts in a trimer. The interface of a tight dimer is separated by an internal cavity into two "contact areas". The contact area nearest to the centre of the hexamer is most extensive and consists mainly of residues that are quite conserved among arthropodan haemocyanins. All these residues are provided by the second domain of each subunit. Hence, this second domain may play a crucial role in the allosteric functioning of this oxygen transport protein. The dinuclear copper oxygen-binding site resides in the centre of domain 2. This oxygen-binding centre is not fully accessible from the solvent. Three large cavities occur, however, within each subunit at the interfaces of the three domains. All three cavities contain ordered water molecules, and two of them are accessible from the surrounding solvent. These cavities may play a role in facilitating fast movement of dioxygen towards the binding site, which is situated in a highly conserved, rather hydrophobic core. A detailed definition of the geometry of the copper site is, of course, not possible at the limited resolution of 3.2 A. Nevertheless, it is possible to conclude that each copper is co-ordinated by two, more or less tightly bound, histidine ligands and one more distant histidine residue. The six histidine residues utilize their N epsilon atoms for copper co-ordination, while their N delta atoms are engaged in hydrogen bonds with conserved residues or water molecules. The two distant histidine ligands are located in apical positions and are on opposite sides with respect to the plane approximately defined by the four more tightly bound histidine ligands and the two copper ions. The copper-to-copper distance is 3.5 to 3.6 A in four of the subunits, but this distance deviates considerably in two others.(ABSTRACT TRUNCATED AT 400 WORDS)

Secondary reference #1

• Title: Spectroscopic investigations of panulirus interruptus hemocyanin in the crystalline state.
• Authors: A.Volbeda, M.C.Feiters, M.G.Vincent, E.Bouwman, B.Dobson, K.H.Kalk, J.Reedijk, W.G.Hol.
• Ref.: Eur J Biochem, 1989, 181, 669-673.
• PubMed id: 2543566

Secondary reference #2

• Title: Pseudo 2-Fold symmetry in the copper-Binding domain of arthropodan haemocyanins. Possible implications for the evolution of oxygen transport proteins.
• Authors: A.Volbeda, W.G.Hol.
• Ref.: J Mol Biol, 1989, 206, 531-546.
• PubMed id: 2716060

Secondary reference #3

• Title: Panulirus interruptus hemocyanin. The amino acid sequence of subunit b and anomalous behaviour of subunits a and b on polyacrylamide gel electrophoresis in the presence of sds.
• Authors: P.A.Jekel, H.J.Bak, N.M.Soeter, J.M.Vereijken, J.J.Beintema.
• Ref.: Eur J Biochem, 1988, 178, 403-412.
• PubMed id: 3208765

Secondary reference #4

• Title: Panulirus interruptus hemocyanin. The elucidation of the complete amino acid sequence of subunit a.
• Authors: H.J.Bak, J.J.Beintema.
• Ref.: Eur J Biochem, 1987, 169, 333-348.
• PubMed id: 3480218

Secondary reference #5

• Title: Structure determination of panulirus interruptus haemocyanin at 3.2 a resolution. Successful phase extension by sixfold density averaging.
• Authors: W.P.Gaykema, A.Volbeda, W.G.Hol.
• Ref.: J Mol Biol, 1986, 187, 255-275.
• PubMed id: 3701867

Secondary reference #6

• Title: The structure of arthropod hemocyanins.
• Authors: B.Linzen, N.M.Soeter, A.F.Riggs, H.J.Schneider, W.Schartau, M.D.Moore, E.Yokota, P.Q.Behrens, H.Nakashima, T.Takagi.
• Ref.: Science, 1985, 229, 519-524. [DOI no: 10.1126/science.4023698]
• PubMed id: 4023698

Secondary reference #7

• Title: 3.2 angstroms structure of the copper-Containing, Oxygen-Carrying protein panulirus interruptus haemocyanin
• Authors: W.P.J.Gaykema, W.G.J.Hol, J.M.Vereijken, N.M.Soeter, H.J.Bak, J.J.Beintema.
• Ref.: nature, 1984, 309, 23.