Complete subunit sequences, structure and evolution of the 6 × 6‐mer hemocyanin from the common house centipede, Scutigera coleoptrata

Abstract

Hemocyanins are large oligomeric copper‐containing proteins that serve for the transport of oxygen in many arthropod species. While studied in detail in the Chelicerata and Crustacea, hemocyanins had long been considered unnecessary in the Myriapoda. Here we report the complete molecular structure of the hemocyanin from the common house centipede Scutigera coleoptrata (Myriapoda: Chilopoda), as deduced from 2D‐gel electrophoresis, MALDI‐TOF mass spectrometry, protein and cDNA sequencing, and homology modeling. This is the first myriapod hemocyanin to be fully sequenced, and allows the investigation of hemocyanin structure–function relationship and evolution. S. coleoptrata hemocyanin is a 6 × 6‐mer composed of four distinct subunit types that occur in an approximate 2 : 2 : 1 : 1 ratio and are 49.5–55.5% identical. The cDNA of a fifth, highly diverged, putative hemocyanin was identified that is not included in the native 6 × 6‐mer hemocyanin. Phylogenetic analyses show that myriapod hemocyanins are monophyletic, but at least three distinct subunit types evolved before the separation of the Chilopoda and Diplopoda more than 420 million years ago. In contrast to the situation in the Crustacea and Chelicerata, the substitution rates among the myriapod hemocyanin subunits are highly variable. Phylogenetic analyses do not support a common clade of Myriapoda and Hexapoda, whereas there is evidence in favor of monophyletic Mandibulata.

The evolution of arthropod heads: reconciling morphological, developmental and palaeontological evidence

“…In contrast, there is ample evidence from development and morphology that supports the Mandibulata as a monophyletic group (see Edgecombe 2004;Harzsch et al 2005a;Scholtz and Edgecombe 2005). Furthermore, some phylogenetic studies based on molecular data and combined datasets support Mandibulata as well (Edgecombe et al 2000;Giribet et al 2001Giribet et al , 2005Kusche et al 2003). Accordingly, the Mandibulata concept is used here for the discussion of head evolution and trilobite relationships.…”

Molecular characterization of hemocyanin and hexamerin from the firebrat Thermobia domestica (Zygentoma)

“…Within the last 30 years, presence and properties of hemocyanins have been thoroughly studied in Chelicerata and malacostracan Crustacea. However, their widespread occurrence in other arthropods (Onychophora, Myriapoda and Hexapoda) has been discovered only recently (Jaenicke et al, 1999;Kusche et al, 2002Kusche et al, , 2003Hagner-Holler et al, 2004).…”

Molecular and functional characterization of hemocyanin of the giant African millipede,Archispirostreptus gigas

“…No additional subunit could be detected despite extensive screening and additional RT-PCR experiments with the ESTs of this species (Meusemann et al, 2010). Thus, in contrast to most arthropod Hcs (Markl and Decker, 1992;Kusche et al, 2003), the native A. gigas Hc likely consists of only a single subunit type.…”

“…Hc. The two diplopod Hcs are a sister group of the HcA subunit of Scutigera coleoptrata (Kusche et al, 2003), while the other four Hc, hemocyanin; Pm, median O2 tension; P50, O2 tension at 50% oxygenation; n50, Hill s cooperativity coefficient at 50% oxygenation; nmax, maximal cooperativity coefficient; KT and KR, oxygen dissociation constants for the tense state and relaxed state, respectively; c=KT/KR; G, free energy of cooperativity; q, the number of interacting O2-binding sites; and L, allosteric constant. *Could not be determined in the data fitting.…”