Research Interests
My group is interested in the assembly and activation of membrane-bound proteins using techniques that are capable of observing individual molecules. In general, our understanding of biomolecules is derived from experiments where the average properties of a population are measured. By using techniques capable of resolving the fluorescence from a single molecule, it is possible to resolve more than just these ensemble-averaged attributes. For example, we can measure the distribution of a particular molecular property, or the reaction pathway followed by an individual molecule.
  To give an analogy: If we were examining the heights of people in a crowd rather than the properties of molecules, the bulk behaviour would yield only the average height. However, if it were possible to look at the crowd person by person, studying the distribution of heights, a more meaningful insight could be made. The complexity of biological molecules, in both their underlying dynamic structure and their interactions, makes this single-molecule approach particularly valuable.
We are interested in using these single-molecule methods to help us understand the mechanisms that govern the behaviour of biomolecules. In particular, we are interested in how protein complexes form and how small chemical messengers can influence the conformation and assembly of membrane-bound receptors.
Our principal tools are single-molecule laser microscopy and single-channel electrical recording. We also use molecular biology to engineer proteins that we can label with a fluorescent marker. These labelled proteins are then interrogated under the microscope. We collect data from many tens of thousands of molecules, and interpreting this data often requires the development of new computational tools and models.
Assembly of pore-forming proteins
 In
collaboration with Hagan
Bayley we are studying the mechanism of pore-protein assembly.
Pore-forming bacterial toxins such as Staphylococcal a-hemolysin (a-HL)
provide an excellent model for studying the oligomerisation of membrane
proteins, due to the high stability and solubility of the monomeric
subunits. The bulk behaviour of a-HL has been characterised in detail;
with known crystal structure, and extensive investigation of the electrical
properties of the pore. The current working model for pore assembly
involves two intermediates. We are currently testing this model of
pore assembly by studying the interactions of single fluorescently
labelled a-HL monomers.
Ligand binding and gating in ion-channels
 Using simultaneous single-molecule fluorescence and single-channel electrical recording we are studying the mechanism by which ion channel gating is regulated by ligand binding. The gating of ion channels in response to the binding of chemical ligands is a critical step in many signal transduction pathways. Working with Stephen Tucker, we are interested in understanding the relationship between binding, transduction and gating at the single-molecule level.
New single-molecule methods
Our group is also developing new methods to image and manipulate lipid bilayers and membrane proteins.
Selected Publications
- Membrane protein stoichiometry determined from the step-wise photobleaching of dye-labelled subunits.
Das SK, Darshi M, Cheley S, Wallace MI, Bayley H.
ChemBioChem. (2007) 8, 9, 994.
- Prepore for a breakthrough.
Bayley H, Jayasinghe L, Wallace MI.
Nat.Struct.Mol.Biol. (2005) 12, 1
- A model of stereocilia adaptation based on single molecule mechanical studies of myosin-I.
Batters C, Wallace MI, Coluccio LM, Molloy JE.
Phil.Trans.Royal.Soc. (2004) 359, 1895.
- Nanometre resolution of myosin-1 motility.
Wallace MI, Batters C, Coluccio LM, Molloy JE.
IEE Proceedings: Nanobiotechnology. (2003) 150, 134.
- Combined single-molecule force and fluorescence measurements for biology.
Wallace MI, Molloy JE, Trentham, DR.
Journal of Biology. (2003) 2, 4.
- Photon counting histogram for one-photon excitation.
Perroud TD, Bo HA Wallace MI, Zare RN.
ChemPhysChem. (2003) 4, 1121.
- Non-Arrhenius kinetics for the loop closure of a DNA hairpin-loop.
Wallace MI, Ying LM, Balasubramanian S, Klenerman D.
PNAS. (2001) 98, 5584-5589.
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