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

• Published in: Biochimica et biophysica acta Vol. 1840; no. 9; pp. 2862 - 2877
• Main Authors: Sindhu Kumari, S., Varadaraj, Kulandaiappan
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.09.2014
• Subjects: Amino Acid Substitution; Animals; AQP0; AQP0 N-/ C-terminal truncation; Aquaporins - genetics; Aquaporins - metabolism; Cell Adhesion Molecules - genetics; Cell Adhesion Molecules - metabolism; Cell Membrane - genetics; Cell Membrane - metabolism; Cell-to-cell adhesion; Eye Proteins - genetics; Eye Proteins - metabolism; Lens, Crystalline - cytology; Lens, Crystalline - metabolism; Mice; Mutagenesis, Site-Directed; Mutation, Missense; Oocytes; Protein Processing, Post-Translational - physiology; Protein Transport - physiology; Refractive index; Spherical aberration; Water permeability; Xenopus laevis; AQP0 N-/ C-terminal truncation; Cell-to-cell adhesion; Refractive index; AQP0; Spherical aberration; Water permeability
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2014.05.002

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. 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. 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). 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. 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. [Display omitted] •N- and proximal end of C-terminus of AQP0 are important for protein trafficking.•Water permeability and adhesion are not affected by AQP0 N- or C-terminal cleavage.•N- and C-terminal truncations of AQP0 appear to be a fiber cell maturation event.•AQP0 N- and C-terminal truncations may aid in the compaction of cytosolic proteins.•AQP0 may assist in adjusting lens refractive index to prevent spherical aberration.