Postfixation detergent treatment liberates the membrane modelling protein Pex11β from peroxisomal membranes

Pex11 proteins are involved in membrane remodelling processes of peroxisomes, and are key components of peroxisomal division and proliferation. In mammals, three Pex11 isoforms, Pex11 alpha, Pex11 beta, and Pex11 gamma exist. Here we demonstrate that Pex11 beta, but not Pex11 alpha or Pex11 gamma, is almost exclusively extracted from peroxisomal membranes of paraformaldehyde-fixed cells by permeabilisation with the non-ionic detergent Triton X-100. This results in diminished detection of Myc-Pex11 beta in immunofluorescence preparations and appearance of the protein in the Triton X-100 extract. To our knowledge, Pex11 beta is the first peroxisomal membrane protein showing such a peculiar behaviour. Loss of Pex11 beta can be avoided by permeabilisation with digitonin, the addition of glutaraldehyde to the fixative, or the expression of a Pex11 fusion protein with a larger protein tag (e.g. YFP). Our observations further point to different functions and biochemical properties of the Pex11 isoforms within the peroxisomal membrane and during peroxisome proliferation.