Comparison of the X-ray absorption properties of the binuclear active site of molluscan and arthropodan hemocyanins

• Published in: Journal of biological inorganic chemistry Vol. 7; no. 1-2; pp. 120 - 128
• Main Authors: Sabatucci, A, Ascone, I, Bubacco, L, Beltramini, M, Muro, DiP, Salvato, B
• Format: Journal Article
• Language: English
• Published: Germany 01.01.2002
• Subjects: Animals; Arthropods - metabolism; Binding Sites - physiology; Copper - chemistry; Copper - metabolism; Hemocyanins - chemistry; Hemocyanins - metabolism; Mollusca - metabolism; Oxygen - metabolism; Protein Binding - physiology; Species Specificity; Spectrum Analysis - methods; X-Rays
• ISSN: 0949-8257; 1432-1327
• DOI: 10.1007/s007750100272

The structural characteristics of oxy- and deoxy-hemocyanins have been investigated using X-ray absorption spectroscopy both in the near-edge (XANES) and for the first shell contribution in the EXAFS region. Several arthropodan and molluscan hemocyanins have been studied in order to trace the inter- and intra-phyla differences. The XANES spectra of oxy-hemocyanins of the different species are remarkably similar, consistent with a very strongly conserved co-ordination geometry of the copper active site. In contrast, small but significant differences are observed between the deoxy-forms of arthropodan and molluscan proteins. In particular, the XANES spectra of deoxy-arthropodan hemocyanins (with the exception of L. polyphemus Hc) show a more intense edge feature at approximately 8983 eV. This difference is tentatively assigned to a more planar geometry of the copper-ligands system in the arthropodan rather than in the molluscan proteins. The first shell analysis of the EXAFS modulation is consistent with the presence of n=3Nepsilon(2) imidazole nitrogens at an average distance of 1.92 +/- 0.03 A from copper in all the deoxy-hemocyanins investigated. Binding of dioxygen results for all hemocyanins in the increase of the number of first shell back-scattering atoms to n=5 with average distances of 1.93 A. Alternatively, by separating the contribution of Nepsilon(2) imidazole nitrogens and of peroxide O-atoms, n=3 ligands at 1.98 +/- 0.03 A and n=2 ligands at 1.87 +/- 0.03 A are found.