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Structural biology of ion channels and transporters

We use a combination of x-ray crystallography and other biophysical and biochemical techniques to study the stereochemistry of signaling and transport through biological membranes.

Structural studies of TRP channels

The goal is to elucidate the gating mechanism of TRP ion channels involved in temperature sensing and understand modulatory interactions of proteins and small molecules with TRP channels. We are particularly interested in determining the molecular mechanism of temperature sensing. We therefore focus on the temperature-sensing TRP channels such as TRPV1, TRPV2, and TRPM8. Several temperature-sensing TRP channels like TRPV1, TRPV2 and TRPA1 are expressed in nociceptor neurons, and therefore responsible for pain sensations in response to noxious stimuli. The biophysical and biochemical mechanisms of pain and heat sensing are not only of academic interest, but also of medical and pharmacological interest. With structures of these TRP channels, we will be better equipped to design chemical inhibitors, which could potentially be used therapeutically.

Structural studies of TAP, the transporter associated with antigen processing

The goal is to elucidate how TAP, a heterodimer of two membrane-spanning proteins, TAP1 and TAP2, transports peptides generated by the proteasome in the cytosol into the endoplasmic reticulum for loading onto MHC class I molecules. Loaded class I molecules then travel to the cell surface and present the peptides to T cells, an immune system mechanism to recognize and eliminate deregulated or tumorigenic cells, virally-infected cells and foreign cells (e.g. graft rejection). We have undertaken structural studies of the cytosolic C-terminal ATPase domains of TAP1 (cTAP1) and TAP2 (cTAP2) to understand how ATP binding and hydrolysis fuels peptide transport. We have solved the cTAP1 structure in the ADP-bound monomeric state and are now focusing our efforts towards a structure of the cTAP1-cTAP2 heterodimer. Furthermore, we have overexpressed the full-length TAP ABC transporter in insect cells and, using cell-based and in vitro biochemical assays, determine the effects of deletions and substitutions within the TAP1 and TAP2 proteins.

Structural studies of Nramp proteins

Metals such as iron and manganese are essential to physiological processes such as oxygen transport and energy metabolism. Nramps (natural resistance-associated macrophage proteins) are transporters that allow the proton-driven import of divalent metal ions into cells. Humans have two Nramp homologs. Nramp1 transports metals across the phagolysosomal membrane of macrophages and other phagocytic cells, and is important for the antimicrobial function of these cells. DMT1 (divalent metal transporter 1, also known as Nramp2 or DCT1) is responsible for absorption of dietary iron and manganese in the proximal duodenum. Furthermore, DMT1 allows assimilation of transferrin-bound iron by the red blood cell precursors in specialized endosomal compartments. The goal of this proposal is to determine the molecular mechanism of metal-ion transport by the Nramp family of proteins through structural studies of a bacterial Nramp protein, MntH.