title: Intact and N- or C-terminal end truncated AQP0 function as open water channels and cell-to-cell adhesion proteins: end truncation could be a prelude for adjusting the refractive index of the lens to prevent spherical aberration.
abstract: BACKGROUND
  Investigate the impact of natural N- or C-terminal post-translational truncations of lens mature fiber cell Aquaporin 0 (AQP0) on water permeability (Pw) and cell-to-cell adhesion (CTCA) functions.
  
  
  METHODS
  The following deletions/truncations were created by site-directed mutagenesis (designations in parentheses): Amino acid residues (AA) 2-6 (AQP0-N-del-2-6), AA235-263 (AQP0-1-234), AA239-263 (AQP0-1-238), AA244-263 (AQP0-1-243), AA247-263 (AQP0-1-246), AA250-263 (AQP0-1-249) and AA260-263 (AQP0-1-259). Protein expression was studied using immunostaining, fluorescent tags and organelle-specific markers. Pw was tested by expressing the respective complementary ribonucleic acid (cRNA) in Xenopus oocytes and conducting osmotic swelling assay. CTCA was assessed by transfecting intact or mutant AQP0 into adhesion-deficient L-cells and performing cell aggregation and adhesion assays.
  
  
  RESULTS
  AQP0-1-234 and AQP0-1-238 did not traffic to the plasma membrane. Trafficking of AQP0-N-del-2-6 and AQP0-1-243 was reduced causing decreased membrane Pw and CTCA. AQP0-1-246, AQP0-1-249 and AQP0-1-259 mutants trafficked properly and functioned normally. Pw and CTCA functions of the mutants were directly proportional to the respective amount of AQP0 expressed at the plasma membrane and remained comparable to those of intact AQP0 (AQP0-1-263).
  
  
  CONCLUSIONS
  Post-translational truncation of N- or C-terminal end amino acids does not alter the basal water permeability of AQP0 or its adhesive functions. AQP0 may play a role in adjusting the refractive index to prevent spherical aberration in the constantly growing lens.
  
  
  CONCLUSIONS
  Similar studies can be extended to other lens proteins which undergo post-translational truncations to find out how they assist the lens to maintain transparency and homeostasis for proper focusing of objects on to the retina.
authors.affiliation: Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sindhu Kumari
authors.affiliation: Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA; SUNY Eye Institute, New York, NY, USA. Electronic address: kulandaiappan.varadaraj@stonybrook.edu.
authors.forename: Kulandaiappan
authors.initials: K
authors.lastname: Varadaraj
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D007908:Lens, Crystalline / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D009865:Oocytes; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D021381:Protein Transport / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D020346:Aquaporins; D015815:Cell Adhesion Molecules; D005136:Eye Proteins; C030328:aquaporin 0
keywords: AQP0; AQP0 N-/ C-terminal truncation; Cell-to-cell adhesion; Refractive index; Spherical aberration; Water permeability