Spatiotemporal stop-and-go dynamics of the mitochondrial TOM core complex correlates with channel activity
TOM diffusion is coupled to permeability. Here we show the correlation between lateral protein diffusion and channel activity of the general protein import pore of mitochondria (TOM-CC) in membranes resting on ultrathin hydrogel films. Using electrode-free optical recordings of ion flux, we find that TOM-CC switches reversibly between three states of ion permeability associated with protein diffusion. While freely diffusing TOM-CC molecules are predominantly in a high permeability state, non-mobile molecules are mostly in an intermediate or low permeability state. We explain this behavior by the mechanical binding of the two protruding Tom22 subunits to the hydrogel and a concomitant combinatorial opening and closing of the two β-barrel pores of TOM-CC. TOM-CC could thus represent a β-barrel membrane protein complex to exhibit membrane state-dependent mechanosensitive properties, mediated by its two Tom22 subunits.
Single-molecule FRET imaging of beta-barrel folding. In comparison to globular proteins, the spontaneous folding and insertion of β-barrel membrane proteins is surprisingly slow, typically occurring on the order of minutes. Using single-molecule Förster Resonance Energy Transfer to report on the folding of fluorescently-labelled Outer Membrane Protein G we measured the real-time insertion of a β-barrel membrane protein from an unfolded state. Folding events were rare, and fast (<20 ms); occurring immediately upon arrival at the membrane. This combination of infrequent, but rare, folding resolves this apparent dichotomy between slow ensemble kinetics, and the typical timescales of biomolecular folding.
Raj Paul Raj joins us as a Newton-Bhabha research internship as part of his PhD programme in IACS, India. He brings synthetic ion channels for single channel electrophysiology and single molecule imaging in Droplet Interface Bilayers.
Lucian Heeler Lucian joins the group as part of the KCL BiPAS CDT programme. In collaboration with Jeremy Carlton we will use new single-molecule tools and artificial membrane mimics to understand the mechanism of membrane fission by the Endosomal Sorting Complex Required for Transport (ESCRT).
Guanzong Zhai Supported by the King’s-China Scholarship Council PhD Scholarship programme (K-CSC), Guanzhong Zhai joins the Wallace group working on on new methods for artificial cell fabrication.
Designer alpha-helical barrels.
The design of peptides that assemble in membranes to form functional ion channels is challenging. Specifically, hydrophobic interactions must be designed between the peptides and at the peptide–lipid interfaces simultaneously. Here, we take a multi-step approach towards this problem. First, we use rational de novo design to generate water-soluble α-helical barrels with polar interiors, and confirm their structures using high-resolution X-ray crystallography. These α-helical barrels have water-filled lumens like those of transmembrane channels. Next, we modify the sequences to facilitate their insertion into lipid bilayers. Single-channel electrical recordings and fluorescent imaging of the peptides in membranes show monodisperse, cation-selective channels of unitary conductance.
Zhongdao Li After a KURF summer studentship failed to dissuade Zhongdao from working in the lab he joins us for a PhD working on new methods to link artificial cells and real cells.