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BFSP1 C-terminal domains released by post-translational processing events can alter significantly the calcium regulation of AQP0 water permeability

Tapodi, Antal; Clemens, Daniel; Uwineza, Alice; Goldberg, Martin; Thinon, Emmanuelle; Heal, William; Tate, Edward; Nemeth-Cahalan, Karinne; Vorontsova, Irene; Jarrin, Miguel; Hall, James; Quinlan, Roy

BFSP1 C-terminal domains released by post-translational processing events can alter significantly the calcium regulation of AQP0 water permeability Thumbnail


Authors

Antal Tapodi

Daniel Clemens

Alice Uwineza

Emmanuelle Thinon

William Heal

Edward Tate

Karinne Nemeth-Cahalan

Irene Vorontsova

Miguel Jarrin

James Hall



Abstract

BFSP1 (beaded filament structural protein 1, filensin) is a cytoskeletal protein expressed in the eye lens. It binds AQP0 in vitro and its C-terminal sequences have been suggested to regulate the water channel activity of AQP0. A myristoylated fragment from the C-terminus of BFSP1 was found in AQP0 enriched fractions. Here we identify BFSP1 as a substrate for caspase-mediated cleavage at several C-terminal sites including D433. Cleavage at D433 exposes a cryptic myristoylation sequence (434–451). We confirm that this sequence is an excellent substrate for both NMT1 and 2 (N-myristoyl transferase). Thus caspase cleavage may promote formation of myristoylated fragments derived from the BFSP1 C-terminus (G434-S665). Myristoylation at G434 was, however, not required for plasma membrane association, but biochemical fractionation and immunogold labeling confirmed that C-terminal BFSP1 fragments containing the myristoylation sequence colocalised with AQP0 in the same plasma membrane compartments of lens fibre cells. To determine the functional significance of the association of BFSP1 G434-S665 sequences with AQP0, we measured AQP0 water permeability in Xenopus oocytes co-transfected with transcripts expressing both AQP0 and various naturally occurring C-terminus fragments of BFSP1. We found that different fragments dramatically alter the response of AQP0 to different concentrations of Ca2+. The full-length C-terminal fragment (G434-S665) eliminates calcium regulation altogether. Shorter fragments enhance regulation by elevated calcium or reverse the wild type response. In particular, elimination of the myristoylation site by the mutation G434A reverses the order of water permeability sensitivity to different Ca2+ concentrations.

Citation

Tapodi, A., Clemens, D., Uwineza, A., Goldberg, M., Thinon, E., Heal, W., …Quinlan, R. (2019). BFSP1 C-terminal domains released by post-translational processing events can alter significantly the calcium regulation of AQP0 water permeability. Experimental Eye Research, 185, Article 107585. https://doi.org/10.1016/j.exer.2019.02.001

Journal Article Type Article
Acceptance Date Feb 3, 2019
Online Publication Date Feb 18, 2019
Publication Date Aug 31, 2019
Deposit Date Feb 13, 2019
Publicly Available Date Jul 16, 2019
Journal Experimental Eye Research
Print ISSN 0014-4835
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 185
Article Number 107585
DOI https://doi.org/10.1016/j.exer.2019.02.001

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