Crystallographic analysis of oxygenated and deoxygenated states of arthropod hemocyanin shows unusual differences.
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.
Magnus
K A
KA
Department of Biochemistry, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4935.
Hazes
B
B
Ton-That
H
H
Bonaventura
C
C
Bonaventura
J
J
Hol
W G
WG
D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D006433:Hemocyanins / Q000031:analogs & derivatives* / Q000737:chemistry*; D006737:Horseshoe Crabs / Q000737:chemistry*; D008121:Nephropidae / Q000737:chemistry; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation; D013045:Species Specificity
C019325:deoxyhemocyanin; C021724:oxy-beta-hemocyanin; D003300:Copper; D006433:Hemocyanins; D010100:Oxygen