title: Self-assembled lipid and membrane protein polyhedral nanoparticles.
abstract: We demonstrate that membrane proteins and phospholipids can self-assemble into polyhedral arrangements suitable for structural analysis. Using the Escherichia coli mechanosensitive channel of small conductance (MscS) as a model protein, we prepared membrane protein polyhedral nanoparticles (MPPNs) with uniform radii of ∼ 20 nm. Electron cryotomographic analysis established that these MPPNs contain 24 MscS heptamers related by octahedral symmetry. Subsequent single-particle electron cryomicroscopy yielded a reconstruction at ∼ 1-nm resolution, revealing a conformation closely resembling the nonconducting state. The generality of this approach has been addressed by the successful preparation of MPPNs for two unrelated proteins, the mechanosensitive channel of large conductance and the connexon Cx26, using a recently devised microfluidics-based free interface diffusion system. MPPNs provide not only a starting point for the structural analysis of membrane proteins in a phospholipid environment, but their closed surfaces should facilitate studies in the presence of physiological transmembrane gradients, in addition to potential applications as drug delivery carriers or as templates for inorganic nanoparticle formation.
authors.affiliation: Molecular, Cellular, and Developmental Biology and Mechanical Engineering, University of Colorado at Boulder, Boulder, CO 80309.
authors.forename: Tamara
authors.initials: T
authors.lastname: Basta
authors.forename: Hsin-Jui
authors.initials: HJ
authors.lastname: Wu
authors.forename: Mary K
authors.initials: MK
authors.lastname: Morphew
authors.forename: Jonas
authors.initials: J
authors.lastname: Lee
authors.forename: Nilanjan
authors.initials: N
authors.lastname: Ghosh
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Lai
authors.forename: John M
authors.initials: JM
authors.lastname: Heumann
authors.forename: Keeshia
authors.initials: K
authors.lastname: Wang
authors.forename: Y C
authors.initials: YC
authors.lastname: Lee
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Rees
authors.forename: Michael H B
authors.initials: MH
authors.lastname: Stowell
mesh_terms: D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D007473:Ion Channels / Q000737:chemistry*; D046210:Microfluidic Analytical Techniques; D008958:Models, Molecular; D053758:Nanoparticles / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D029968:Escherichia coli Proteins; D007473:Ion Channels; C469542:MscS protein, E coli
keywords: electron microscopy; membrane protein structure; microfluidic devices; proteoliposomes