The Evolution of Hexamerins and the Phylogeny of Insects

Abstract

The evolutionary relationships among arthropod hemocyanins and insect hexamerins were investigated. A multiple sequence alignment of 12 hemocyanin and 31 hexamerin subunits was constructed and used for studying sequence conservation and protein phylogeny. Although hexamerins and hemocyanins belong to a highly divergent protein superfamily and only 18 amino acid positions are identical in all the sequences, the core structures of the three protein domains are well conserved. Under the assumption of maximum parsimony, a phylogenetic tree was obtained that matches perfectly the assumed phylogeny of the insect orders. An interesting common clade of the hymenopteran and coleopteran hexamerins was observed. In most insect orders, several paralogous hexamerin subclasses were identified that diversified after the splitting of the major insect orders. The dipteran arylphorin/LSP-1-like hexamerins were subject to closer examination, demonstrating hexamerin gene amplification and gene loss in the brachyceran Diptera. The hexamerin receptors, which belong to the hexamerin/hemocyanin superfamily, diverged early in insect evolution, before the radiation of the winged insects. After the elimination of some rapidly or slowly evolving sequences, a linearized phylogenetic tree of the hexamerins was constructed under the assumption of a molecular clock. The inferred time scale of hexamerin evolution, which dates back to the Carboniferous, agrees with the available paleontological data and reveals some previously unknown divergence times among and within the insect orders.

The antiapoptotic activity of insect IAPs requires activation by an evolutionarily conserved mechanism

“…20 Across the wide range of insect IAPs examined, we noticed evolutionary conservation of the DXXDkN motif, in addition to the BIR and RING domains, highlighting its evolutionary and functional significance. Our results demonstrate that whereas the DXXDkN motif does not contribute to effector caspase binding, it is required to neutralise effector caspases and suppress cell death.…”

“…19 Moreover, this DIAP1-associated antiapoptotic mechanism has, so far, not been observed outside of the Drosophila genus. To gain insights into the relevance of the N-end-rule-based antiapoptotic mechanism, we studied the effects of almost 300 million years of evolutionary selection pressure 20 on IAP-mediated caspase regulation. Through comparison of various insect IAPs, ranging from Diptera, Lepidoptera and Hymenoptera, we uncovered a striking mechanistic conservation in caspase regulation.…”

Social exploitation of hexamerin: RNAi reveals a major caste-regulatory factor in termites

“…Insect hexamerins are part of a large family of hexameric proteins that are closely linked with diversifying evolution in arthropods (24). Strong evidence suggests that hexamerin-like proteins of terrestrial insects evolved from oxygen-carrying hemocyanins of ancestral aquatic insects and crustaceans (24,25). In terrestrial insects, the hexamerins have acquired diverse storage (26) and hormone-binding functions (19).…”

Identification, Structure, and Properties of Hemocyanins from Diplopod Myriapoda

“…Each subunit carries one oxygen molecule by the virtue of two copper ions that are coordinated by six histidine residues (4). Hemocyanins are members of a functionally and structurally diverse protein superfamily that includes arthropod tyrosinases (prophenoloxidases), crustacean nonrespiratory pseudo-hemocyanins (cryptocyanins), insect hexamerins, and dipteran hexamerin receptors (5)(6)(7)(8)(9)(10).…”