tailieunhanh - Báo cáo khoa học: Subunit sequences of the 4 · 6-mer hemocyanin from the golden orb-web spider, Nephila inaurata Intramolecular evolution of the chelicerate hemocyanin subunits

The transport of oxygen in the hemolymph of many arth-ropod and mollusc species is mediated by large copper-proteins that are referred to as hemocyanins. Arthropod hemocyanins are composed of hexamers and oligomers of hexamers. Arachnid hemocyanins usually form 4·6-mers consisting of seven distinct subunit types (termed a–g), although in some spider taxa deviations from this standard scheme have been observed. | Eur. J. Biochem. 270 3432-3439 2003 FEBS 2003 doi Subunit sequences of the 4 X 6-mer hemocyanin from the golden orb-web spider Nephila inaurata Intramolecular evolution of the chelicerate hemocyanin subunits Anne Averdam Jurgen Markl and Thorsten Burmester Institute of Zoology Johannes Gutenberg University Mainz Germany The transport of oxygen in the hemolymph of many arthropod and mollusc species is mediated by large copperproteins that are referred to as hemocyanins. Arthropod hemocyanins are composed of hexamers and oligomers of hexamers. Arachnid hemocyanins usually form 4 X 6-mers consisting of seven distinct subunit types termed a-g although in some spider taxa deviations from this standard scheme have been observed. Applying immunological and electrophoretic methods six distinct hemocyanin subunits were identified in the red-legged golden orb-web spider Nephila inaurata madagascariensis Araneae Tetragnathi-dae . The complete cDNA sequences of six subunits were obtained that corresponded to a- b- d- e- f- and g-type subunits. No evidence for a c-type subunit was found in this species. The inclusion of the N. inaurata hemocyanins in a multiple alignment of the arthropod hemocyanins and the application of the Bayesian method of phylogenetic inference allow for the first time a solid reconstruction of the intramolecular evolution of the chelicerate hemocyanin subunits. The branch leading to subunit a diverged first followed by the common branch of the dimer-forming b and c subunits while subunits d and f as well as subunits e and g form common branches. Assuming a clock-like evolution of the chelicerate hemocyanins a timescale for the evolution of the Chelicerata was obtained that agrees with the fossil record. Keywords Arthropoda Chelicerata evolution hemocyanin subunit diversity. Hemocyanins are large copper-containing respiratory proteins that serve to transport oxygen in many arthropod species 1 2 . Hemocyanins and their .