An evolutionarily distinct chaperone promotes 20S proteasome α-ring assembly in plants
Authors: Adam J Book
Richard D Vierstra
Fionn McLoughlin
Kay Hofmann
David C Gemperline
Richard S Marshall
Journal: Journal of Cell Science (2020)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: Arabidopsis; Chaperone; Core protease; Degradation; Evolution
Affiliations: Department of Biology, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, USA, Department of Genetics, University of Wisconsin, 425 Henry Mall, Madison, Wisconsin 53706, USA, Institute for Genetics, University of Cologne, Zülpicher Straße 47a, 50674 Cologne, Germany

Abstract:  The core protease (CP) subcomplex of the 26S proteasome houses the proteolytic active sites and assumes a barrel shape comprised of four co-axially stacked heptameric rings formed by structurally related α- and β-subunits. CP biogenesis typically begins with the assembly of the α-ring, which then provides a template for β-subunit integration. In eukaryotes, α-ring assembly is partially mediated by two hetero-dimeric chaperones, termed Pba1-Pba2 (Add66) and Pba3-Pba4 (also known as Irc25-Poc4) in yeast. Pba1-Pba2 initially promotes orderly recruitment of the α-subunits through interactions between their C-terminal HbYX or HbF motifs and pockets at the α5-α6 and α6-α7 interfaces. Here, we identified PBAC5 as a fifth α-ring assembly chaperone in Arabidopsis that directly binds the Pba1 homolog PBAC1 to form a trimeric PBAC5-PBAC1-PBAC2 complex. PBAC5 harbors a HbYX motif that docks with a pocket between the α4 and α5 subunits during α-ring construction. Arabidopsis lacking PBAC5, PBAC1 and/or PBAC2 are hypersensitive to proteotoxic, salt and osmotic stresses, and display proteasome assembly defects. Remarkably, whereas PBAC5 is evolutionarily conserved among plants, sequence relatives are also dispersed within other kingdoms, including a scattered array of fungal, metazoan and oomycete species. 

Retracted: No

PubPeer comments:
 Figure S2A, two images seem to overlap (red boxes). Could the authors please check? ![file] , 
 Dear Colleagues, Like you, we are committed to publishing accurate and meaningful scientific data and became concerned about a possible error in the above publication upon receiving a notification from PubPeer. We have now researched the outlined concern and associated raw data and, although we affirm that the conclusions of the paper are correct, we did confirm an error as reported by PubPeer that involves the incorrect duplication of a control BiFC image in Figure S2A. Figure S2A In this Figure, one of the BiFC panels on the lower row (NY-PBAC4 + CY-PBAC2) has been inadvertently taken from the wrong TIF file (NY-PBAC4 + CY-PBAC5), and hence a portion of the panel has been duplicated. In the attached JPEG file, we show the data as published, highlighting the duplicated panels. Below that, we show the original TIF files (with bright field, fluorescence, and merged images) obtained from the confocal microscope. Here, you will clearly see that panels showing either YFP fluorescence alone, or the merged YFP fluorescence and bright field images, for the NY-PBAC4 + CY-PBAC2 panel are different to what was published. Instead, the published data appears to have been taken erroneously from a TIF file corresponding to the NY-PBAC4 + CY-PBAC5 image instead. Clearly, this is an unacceptable error, for which we apologize. We have no defense except carelessness; portions of these images are clearly the same, and we should have taken the NY-PBAC4 + CY-PBAC2 image from the correct TIF file. Please find a corrected version of the Figure in the attached JPEG file. We apologize for this error and regret that it was not detected by us prior to publication. Hopefully, this error will be corrected in an upcoming issue of the Journal of Cell Science. Yours sincerely, Prof Richard D. Vierstra and Dr. Richard S. Marshall , 
 see attached figure file ![file] ![file] , 
 #3 Dear Authors, thank you for your reply, for taking the time to clarify the issue, and for going to correct the literature record. Regards. , 
 Correction, January 2022: https: journals.biologists.com jcs article 135 2 jcs259736 274069 Correction-An-evolutionarily-distinct-chaperone  There was an error in J. Cell Sci. (2020) 133, jcs249862 (doi:10.1242 jcs.249862). In Fig. S2A, two bimolecular fluorescence microscopy (BiFC) confocal microscope images were inadvertently duplicated in the bottom panel. These panels, which both contain only control background fluorescence, were not used to infer any positive interactions and the error does not affect the results or conclusions of the paper. The correct figure is shown below and the online supplementary material has been updated. The authors apologise for the error and any inconvenience this may have caused. , 
 Could the authors please check Figure S2B? There are still two duplications left there. * Cyan boxes: The NY + CY-PBAC2 and the NY + CY-PBAC4 panels appear to overlap * Orange boxes: An unexpected duplications in the NY+CY panel at the bottom. Perhaps the same image was inserted twice and they overlap with each other? ![file] , 
 Dear Dr. Bik: Thanks for identifying the duplicated panels in Figure S2 of this 2020 J Cell Sci by Marshall et al. (133, jcs249862 (doi:10.1242 jcs.249862). After being alerted to the first set of duplicated images by PubPeer, Dr. Marshall was asked to revised the Figure with the appropriate set of BiFC images for a Correction that was generated by him and posted by the journal. After your recent identification of a second set of duplicated images, I personally went over the figure files for this paper prepared by Dr. Marshall and the second author Dr. David Gemperline as part of his Ph.D thesis and found what I believe to be the correct image for the NY + CY-PABAC2 BiFC pair (bottom row, third from the left). I also checked all other pairs of BiFC images. This revised figure, which I hope is now correct, has been sent to J. Cell Sci for posting as a Correction. In addition, I corrected the overlapped image for the NY + CY BiFC pair that somehow became duplicated. This mistake was made by the journal after we sent them the first Correction of the figure. I apologize for these mistakes and any inconvenience they made have generated. Fortunately, these errors did not impact the results nor conclusions of this paper, but were mistakes nonetheless that could have clearly been avoided had Dr. Marshall been more rigorous with his figure preparation. The Corrected Figure S2 is attached. Rick Vierstra ![file] ,