Characterization of the hemoglobin of the backswimmer Anisops deanei (Hemiptera)

While O2-binding hemoglobin-like proteins are present in many insects, prominent amounts of hemoglobin have only been found in a few species. Backswimmers of the genera Anisops and Buenoa (Notonectidae) have high concentrations of hemoglobin in the large tracheal cells of the abdomen. Oxygen from the hemoglobin is delivered to a gas bubble and controls the buoyant density, which enables the bugs to maintain their position without swimming and to remain stationary in the mid-water zone where they hunt for prey. We have obtained the cDNA sequences of three Anisops deanei hemoglobin chains by RT-PCR and RACE techniques. The deduced amino acid sequences show an unusual insertion of a single amino acid in the conserved helix E, but this does not affect protein stability or ligand binding kinetics. Recombinant A. deanei hemoglobin has an oxygen affinity of P50 = 2.4 kPa (18 torr) and reveals the presence of a dimeric fraction or two different conformations. The absorption spectra demonstrate that the Anisops hemoglobin is a typical pentacoordinate globin. Phylogenetic analyses show that the backswimmer hemoglobins evolved within Heteroptera and most likely originated from an intracellular hemoglobin with divergent function.

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► Some backswimmers use hemoglobin to store oxygen for buoyancy control.
► We cloned, sequenced and characterized the hemoglobin of Anisops deanei.
► A. deanei hemoglobin has a unique amino acid insertion in helix E.
► Recombinant A. deanei hemoglobin is a monomer with P50 = 2.4 kPa (18 torr).
► Backswimmer hemoglobins evolved within Heteroptera from an intracellular ancestor.