title: The amoeboidal Dictyostelium aquaporin AqpB is gated via Tyr216 and aqpB gene deletion affects random cell motility.
abstract: BACKGROUND
  Regulation of aquaporin (AQPs) water channels mostly occurs on the transcriptional level or by intracellular trafficking. Direct AQP gating is comparatively rare and is described mainly for fungi and plants. Earlier, we identified a gated water-specific AQP in Dictyostelium discoideum, AqpB, which is opened by truncation of an extended intracellular loop D (AqpB Δ208-219).
  
  
  RESULTS
  We show that Tyr216 of loop D is a key residue in the gating mechanism possibly involving phosphorylation. Mutation of Tyr216 to aspartate or glutamate initiated water permeability (Pf  = 69 μm/s) to the same extent as AqpB Δ208-219, whereas neither replacement of Tyr216 by a positive arginine (Y216R) nor introduction of a negative charge in a neighbouring position (T217D) opened the channel. We overexpressed AqpB wildtype and AqpB Δ208-219 as GFP fusion constructs in Dictyostelium amoebae and found that the truncated, permanently open AqpB yielded cells with reduced capability to cope with hypotonic stress. Genetic deletion of aqpB yielded a strain with significantly reduced speed of random motility (4.5 μm/min vs. 6.3 μm/min of wildtype cells). Yet, chemotaxis towards folate and cAMP was unaffected. In this context, we identified a second, so-far uncharacterised amoeboidal AQP, AqpD, whose role in directed cell locomotion needs to be established.
  
  
  CONCLUSIONS
  Our data add to the completion of the Dictyostelium model for cell motility and show that knowledge on the expression, permeability properties and localisation of amoeboidal AQPs are crucial for further development of the system.
authors.affiliation: Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, 24118, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: von Bülow
authors.forename: André
authors.initials: A
authors.lastname: Golldack
authors.forename: Tineke
authors.initials: T
authors.lastname: Albers
authors.forename: Eric
authors.initials: E
authors.lastname: Beitz
mesh_terms: D020816:Amino Acid Motifs; D020346:Aquaporins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002465:Cell Movement; D002633:Chemotaxis; D004023:Dictyostelium / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion
chemical_list: D020346:Aquaporins
keywords: Dictyostelium; aquaporin; cell motility; gating; water