Publication: Acyrthosiphon pisum AQP2: a multifunctional insect aquaglyceroporin.

February 4th, 2012

Wallace IS, Shakesby AJ, Hwang JH, Choi WG, Martinkova N, Douglas AE and Roberts DM, 2012. Acyrthosiphon pisum AQP2: a multifunctional insect aquaglyceroporin. Biochimica et Biophysica Acta - Biomembranes 1818: 627-635 Pubmed link

We collaborate with Dr Dan Roberts and colleagues at the University of Tennessee, Knoxville, and Natalia Martinkova at the Institute of Vertebrate Biology, Brno, Czech Republic to obtain a functional characterization of the second of two aquaporin genes of the pea aphid, Acyrthosiphon pisum.  This research complements our previous functional analysis of the pea aphid AQP1, which plays a crucial role in water cycling and osmoregulation by the gut.

The abstract of our publication on AQP2: Annotation of the recently sequenced genome of the pea aphid (Acyrthosiphon pisum) identified a gene ApAQP2 (ACYPI009194, Gene ID: 100168499) with homology to the Major Intrinsic Protein/aquaporin superfamily of membrane channel proteins. Phylogenetic analysis suggests that ApAQP2 is a member of an insect-specific clade of this superfamily. Homology model structures of ApAQP2 showed a novel array of amino acids comprising the substrate selectivity-determining “aromatic/arginine” region of the putative transport pore. Subsequent characterization of the transport properties of ApAQP2 upon expression in Xenopus oocytes supports an unusual substrate selectivity profile. Water permeability analyses show that the ApAQP2 protein exhibits a robust mercury-insensitive aquaporin activity. However unlike the water-specific ApAQP1 protein, ApAQP2 forms a multifunctional transport channel that shows a wide permeability profile to a range of linear polyols, including the potentially biologically relevant substrates glycerol, mannitol and sorbitol. Gene expression analysis indicates that ApAQP2 is highly expressed in the insect bacteriocytes (cells bearing the symbiotic bacteria Buchnera) and the fat body. Overall the results demonstrate that ApAQP2 is a novel insect aquaglyceroporin which may be involved in water and polyol transport in support of the Buchnera symbiosis and aphid osmoregulation.

Figure Homology modeling of ApAQP2 conducted by the first author Dr Ian Wallace.  The structural model of the pea aphid AQP2 (fuschia) was superimposed on the experimental AQP4 structure (yellow: pdb 3GD8) as a structural template. The water molecules in the AQP pore are indicated by light blue spheres to show the position of the transport pore. The relative positions of the extracellular space (ex) and the cytosol (cyt) are indicated