Putative new groups of invertebrate water channels based on the snail Helix pomatia L. (Helicidae) MIP protein identification and phylogenetic analysis

• Published in: European journal of cell biology Vol. 95; no. 12; pp. 543 - 551
• Main Authors: Kosicka, Ewa, Grobys, Daria, Kmita, Hanna, Lesicki, Andrzej, Pieńkowska, Joanna R.
• Format: Journal Article
• Language: English
• Published: Germany Elsevier GmbH 01-12-2016
• Subjects: Animals; Aquaporin; Aquaporins - genetics; Aquaporins - metabolism; Helix (Snails) - genetics; Helix (Snails) - metabolism; Helix pomatia; Mollusca; Osmoregulation - physiology; Phylogenetic analysis; Phylogeny; Phylogenetic analysis; Helix pomatia; Mollusca; Aquaporin
• ISSN: 0171-9335; 1618-1298
• DOI: 10.1016/j.ejcb.2016.09.001

•Six transcripts of H. pomatia were identified as putative water channel encoding sequences.•Predicted proteins (HpAQPs) reverse the S. cerevisiae mutant cell phenotype.•All of HpAQPs transport water but not all of them transport glycerol or H2O2.•Only HpAQP1, HpAQP2 and HpAQP5 group with a known vertebrate aquaporin grade.•New groups of Malacoglyceroporins (HpAQP3-4) and Malacoporins (HpAQP6) are proposed.
Water channel proteins, classified as a family of Membrane Intrinsic Proteins (MIPs) superfamily, enable rapid movement of water and small uncharged molecules through biological membranes. Although water channel proteins are required in several important processes characteristic for the animals, such as osmoregulation, mucus secretion, or defense against desiccation, molluscs, until now, have been very poorly explored in this aspect. Therefore, we decided to study MIPs in Helix pomatia L. applied as a model in studies on terrestrial snail physiology.
Our studies consisted in: the snail organ transcriptome sequencing and consecutive bioinformatic analysis of the predicted protein, estimation of the encoding transcript expression (qPCR), investigation of the predicted protein function in the yeast Saccharomyces cerevisiae cells, and the phylogenetic analysis.
We identified six water channel proteins, named HpAQP1 to HpAQP6. All of them were proven to transport water, two of them (HpAQP3 and HpAQP4) were also shown to be able to transport glycerol, and other two (HpAQP5 and HpAQP6) to transport H2O2. Phylogenetic analysis indicated that the proteins either fell into aquaporins (HpAQP1, HpAQP2 and HpAQP5) or formed new groups of invertebrate water channel proteins, not described until now, that we suggest to term malacoglyceroporins (HpAQP3 and HpAQP4) and malacoaquaporins (HpAQP6). Thus, the classification of animal water channels based on the vertebrate proteins and including aquaporin, aquaglyceroporin, S-aquaporin and AQP8-type grades does not reflect diversity of these proteins in invertebrates.
The obtained results provide important data concerning diversity of water channel protein repertoire in aquatic and terrestrial invertebrates and should also contribute to the improvement of animal water channel classification system.