Characterization of CHMP Polymers at the Mesoscale

Abstract

The ESCRT-III is an evolutionary conserved protein complex that mediates membrane remodeling and scission in a variety of cellular contexts. The ESCRT pathway has been extensively studied in vivo and reconstituted in vitro using yeast proteins. The consensus model emerging from these studies is that a sequential recruitment of two subcomplexes, formed by Vps20+Snf7 and Vps2+Vps24, results in membrane constriction and eventually scission. In Homo Sapiens, however, up to 17 ESCRT-III proteins exist, called Charged Multivesicular Body Protein (CHMP 1-7). Vps20 and Vps24 homologous are CHMP6 and CHMP3, respectively. Snf7 is present in three isoforms, namely CHMP4A, B and C. There are two subunits sharing a relative high sequence homology with Vps2, called CHMP2A and CHMP2B. The increased number of ESCRT-III subunits is paralleled by the functional diversification of the complex. In Homo Sapiens it plays multiple roles in topologically equivalent membrane scission events: in nuclear envelope repair, plasma membrane repair, nuclear envelope sealing after mitosis, cytokinesis, MVB formation and virus release. Several models have been proposed to explain how CHMPs are spatially arranged in order to accomplish scission. On the contrary, the mechanical properties of ESCRT-III polymers have never been investigated so far. We have characterized for the first time the mechanical properties of CHMP polymers at the mesoscale, providing strong experimental evidence indicating that modulation of membrane rigidity is an important function of CHMP polymers, and that this property plays an important role in the context of membrane scission. Moreover, we highlight the biological relevance of this property, proposing a novel biological function for CHMP2.