Membrane proteins account for approximately 25% of gene products in organisms. They populate cell and organelle membranes and are essential for communication across these hydrophobic compartmental boundaries. They participate in recognition, transport and transduction processes that are fundamental attributes of living systems. In the work described here, the structure and mechanism of action of a number of membrane protein transporters will be investigated by cryo-electron microscopy and image analysis. Transporters from the ATP Binding Cassette (ABC), Major Facilitator (MFS) and Multi Antimicrobial Toxin Extrusion (MATE) superfamilies will be studied, as these are the current focus of parallel x-ray crystallographic investigations by one of the investigators. Members of the ABC, MFS and MATE superfamilies are of great medical importance as they are responsible for antibiotic and chemotherapy resistance. Cryo-EM and image analysis will be used to calculate 3D maps from (i) helical tubes and 2D crystals of MsbA - an ABC transporter - in various nucleotide-bound and substrate-bound states and, (ii) 2D crystals of FucP - an MFS transporter - with substrate bound. The maps will reveal the structures and provide insights into the transport mechanisms of representative members of these two membrane protein superfamilies. Additional experiments will focus on screening crystallization conditions to improve the order of the existing helical and 2D arrays, and to grow ordered arrays of other membrane proteins for EM structural studies.
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