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Structural Comparison of Cephalopod Hemocyanins: Phylogenetic Significance

1999; Elsevier BV; Volume: 127; Issue: 3 Linguagem: Inglês

10.1006/jsbi.1999.4154

1095-8657

Fabrice Mouche, Nicolas Boisset, Josette Lamy, Franck Zal, Jean Lamy,

Physiological and biochemical adaptations

Hemocyanins, the respiratory molecules of cephalopod mollusks, are hollow cylinders with five internal arches. Three hemocyanins representative of three orders of cephalopods (Benthoctopus species, Octopoda; Vampyroteuthis infernalis, Vampyromorpha; Sepia officinalis, Sepioidea) were subjected to cryoelectron microscopy and three-dimensional (3D) reconstruction. The structure of Benthoctopus hemocyanin, solved at 26.4-Å resolution, possesses arches comprising two identical functional units. The similarity between these functional units and the structure recently observed in X-ray crystallography for Octopus by Cuff et al. (J. Mol. Biol., 1998, 232, 522–529) allows the identification of their N- and C-terminal domains in the 3D reconstruction volume. Conversely, arches present in the 3D reconstruction volume of Sepia hemocyanin (21.8 Å resolution) contain four functional units that are disposed differently. The strong resemblance between the reconstruction volumes of Vampyroteuthis (21.4-Å resolution) and Benthoctopus hemocyanins suggests that Sepioidea diverged from a group containing Octopoda and Vampyromorpha.