Crystallographic analysis of oxygenated and deoxygenated states of arthropod hemocyanin shows unusual differences

• Published in: Proteins, structure, function, and bioinformatics Vol. 19; no. 4; p. 302
• Main Authors: Magnus, K A, Hazes, B, Ton-That, H, Bonaventura, C, Bonaventura, J, Hol, W G
• Format: Journal Article
• Language: English
• Published: United States 01.08.1994
• Subjects: Allosteric Regulation; Animals; Binding Sites; Copper - chemistry; Crystallography, X-Ray; Hemocyanins - analogs & derivatives; Hemocyanins - chemistry; Horseshoe Crabs - chemistry; Nephropidae - chemistry; Oxygen - metabolism; Protein Conformation; Species Specificity
• ISSN: 0887-3585
• DOI: 10.1002/prot.340190405

The X-ray structure of an oxygenated hemocyanin molecule, subunit II of Limulus polyphemus hemocyanin, was determined at 2.4 A resolution and refined to a crystallographic R-factor of 17.1%. The 73-kDa subunit crystallizes with the symmetry of the space group R32 with one subunit per asymmetric unit forming hexamers with 32 point group symmetry. Molecular oxygen is bound to a dinuclear copper center in the protein's second domain, symmetrically between and equidistant from the two copper atoms. The copper-copper distance in oxygenated Limulus hemocyanin is 3.6 +/- 0.2 A, which is surprisingly 1 A less than that seen previously in deoxygenated Limulus polyphemus subunit II hemocyanin (Hazes et al., Protein Sci. 2:597, 1993). Away from the oxygen binding sites, the tertiary and quaternary structures of oxygenated and deoxygenated Limulus subunit II hemocyanins are quite similar. A major difference in tertiary structures is seen, however, when the Limulus structures are compared with deoxygenated Panulirus interruptus hemocyanin (Volbeda, A., Hol, W.G.J.J. Mol. Biol. 209:249, 1989) where the position of domain 1 is rotated by 8 degrees with respect to domains 2 and 3. We postulate this rotation plays an important role in cooperativity and regulation of oxygen affinity in all arthropod hemocyanins.