Complete Sequence of the 24-mer Hemocyanin of the TarantulaEurypelma californicum

Abstract

Hemocyanins are large oligomeric respiratory proteins found in many arthropods and molluscs. The hemocyanin of the tarantula Eurypelma californicum is a 24-mer protein complex with molecular mass of 1,726,459 Da that consists of seven different polypeptides (a-g), each occupying a distinct position within the native molecule. Here we report the complete molecular structure of the E. californicum hemocyanin as deduced from the corresponding cDNAs. This represents the first complex arthropod hemocyanin to be completely sequenced. The different subunits display 52-66% amino acid sequence identity. Within the subunits, the central domain, which bears the active center with the copper-binding sites A and B, displays the highest degree of identity. Using a homology modeling approach, the putative three-dimensional structure of individual subunits was deduced and compared. Phylogenetic analyses suggest that differentiation of the individual subunits occurred 400 -550 million years ago. The hemocyanin of the stemline Chelicerata was probably a hexamer built up of six distinct subunit types a, b/c, d, e, f, and g, whereas that of the early Arachnida was originally a 24-mer that emerged after the differentiation of subunits b and c.

The molecular heterogeneity of hemocyanin: Structural and functional properties of the 4×6-meric protein of Upogebia pusilla (Crustacea)

“…Thus, U. pusilla Hc can be defined as a tetramer of 1 × 6-meric building blocks, in contrast to the 4 × 6-meric Hc of Chelicerates where strong interactions exist between hexamers to build up the 2 × 6-meric half molecules. In the case of tarantula, scorpion and horseshoe crab Hcs the quaternary organization depends on a precise topology of the distribution of the various subunits within the oligomer (Lamy et al, 1981;Markl et al, 1981;Markl and Decker, 1992;Voit et al, 2000;Martin et al, 2007). In particular, linker subunits are responsible for the aggregation of the two 2 × 6-mers and for the highly hierarchical order of interactions (Voit et al, 2000).…”

“…The physico-chemical properties of the protein isolated from the tarantula Eurypelma californicum, have been thoroughly investigated. While the native protein is characterized by a sedimentation coefficient of 37S, several oligomers can be singled out in dissociation experiments (Markl et al, 1982;Savel-Neimann et al, 1988;Voit et al, 2000).…”

“…Two models are known for the ikosatetrameric Hc: the first one refers to chelicerate 4 × 6-mers, fully described for the scorpion Androctonus australis (Lamy et al, 1981) and the tarantula E. californicum (Erker et al, 2006;Voit et al, 2000); the second model has been proposed to describe the thalassinidean shrimps Hc, notably in Callianassa californiensis (Cavellec et al, 1990). It was shown by multivariate statistical analysis applied to computer aligned electron microscopic images that the 4 × 6 Hcs of A. australis and E. californicum are very similar (Bijholt et al, 1982) and fit the model earlier derived for the 4 × 6 half molecules of Limulus polyphemus.…”

Two-photon excitation microscopy of tryptophan-containing proteins

“…One of the hemocyanins best investigated is the 4 ϫ 6-meric hemocyanin (Hc) from the tarantula Eurypelma californicum. The complete sequences of the subunits for this species are known (22), and the oxygen binding is well understood (23)(24)(25). One molecule of oxygen is reversibly bound between two copper atoms in a transverse coordination (26).…”

The molecular heterogeneity of hemocyanin: Its role in the adaptive plasticity of Crustacea

“…Finally, the subunit heterogeneity has been considered to draw the evolutionary dynamics and to trace the ancestral origin (Hughes, 1999;Decker and Terwilliger, 2000;van Holde et al, 2001;Burmester, 2004) of arthropod Hcs. The wide sequence database (about 50 sequences of crustaceans, insects, chelicerates, myriapods, and onychophorans) has allowed for comparison of the phylogenetic relationships among the different subunit types and the diverse molecular evolution among the taxa (Voit et al, 2000;Burmester, 2001;. Hc heterogeneity contributes to the adaptive potential in the respiratory physiology of Crustacea through several mechanisms which can be classified as extrinsic and intrinsic.…”