【SEMINAR】by Prof. Carsten Sachse: Structural basis of p62/SQSTM1 polymers by Electron Cryo-Microscopy

Structural basis of p62/SQSTM1 polymers by electron cryo-microscopy

Carsten Sachse1, 

1 Forschungszentrum Jülich, Ernst-Ruska Centre for Microscopy and Spectroscopy with Electrons (ER-C-3/Structural Biology), 52425 Jülich, Germany

Selective autophagy is the mechanism by which large molecular cargos of various sizes from molecules, organelles to pathogens are specifically sequestered for degradation in the lysosome. We determined a high resolution cryo-EM structure of p62-PB1 filaments revealing the molecular basis of polymer formation and relate these findings with tomographic reconstructions of cellular p62 bodies. It has recently emerged that autophagy receptors support the selective sequestration and transport of specifically marked cargo to nascent autophagosomes [1]. In this process, autophagy receptors recognize ubiquitylated cargo and interact with Atg8/LC3 to bring the cargo-receptor complex in contact with the autophagosomal membrane. The structural details of cargo and receptor assembly giving rise to autophagic vesicles remain to be elucidated. Recently, we showed that autophagy receptor p62/SQSTM-1 assembles into flexible helical polymers [2]. Here, we used recent advances in cryo-EM to generate a helical reconstruction of p62-PB1 filaments. Using EM based structure elucidation in situ we show that large oligomeric and polymeric cargo receptor complexes are the major component of p62 bodies inside of cells and define the architectural requirements of these assemblies for their cargo uptake and degradation using cellular turnover assays. The organization of small receptor proteins into helical polymers provides a cellular mechanism for high selectivity in cargo recognition and a fundamental architectural scaffold enabling cargo encapsulation.

[1]          T. Johansen and T. Lamark, “Selective autophagy mediated by autophagic adapter proteins.,” Autophagy, vol. 7, no. 3, pp. 279–296, Mar. 2011.

[2]          R. Ciuffa, T. Lamark, A. K. Tarafder, A. Guesdon, S. Rybina, W. J. H. Hagen, T. Johansen, and C. Sachse, “The selective autophagy receptor p62 forms a flexible filamentous helical scaffold.,” Cell Rep, vol. 11, no. 5, pp. 748–758, May 2015.