Membrane Proteins and Cell Signaling
Membranes and membrane proteins participate in some of the most important and interesting cellular processes. Energy transduction, cell signaling, membrane excitability, secretion and immune recognition are examples of a few of the processes mediated by membrane proteins. However, the molecular mechanisms by which lipids and membrane proteins accomplish these tasks are largely unknown. We primarily use EPR spectroscopy and high-resolution NMR to investigate the structure and function of membrane proteins.
Protein – membrane surface interactions
Attachment is critical for cell-signaling because it controls protein-protein interactions and the access of enzymes to lipid substrates. We are currently determining the structure and electrostatic interactions made by highly positively charged protein motifs, such as those from MARCKS (the myristoylated alanine rich C-kinase substrate) with negatively charged lipid surfaces. In addition to regulating membrane attachment, these positively charged motifs function to sequester phosphatidylinositol 4,5, bisphosphate (PIP2), and regulate the activity of this phosphorylated inositol lipid within the cytoplasmic membrane. We are also determining the membrane interactions made by protein domains such as C2 domains. C2 domains perform critical roles in membrane trafficking, membrane fusion and membrane repair, and defects in these domains result in forms of muscular dystrophy and deafness.
Active transport across membranes
We are determining the molecular mechanisms by which BtuB transports vitamin B12 across the outer membrane of Escherichia coli. This protein is homologous to FecA, FepA and FhuA, outer membrane iron transport proteins that presumably function by similar mechanisms. These proteins belong to a class of transport proteins for which high-resolution structural models have been obtained, and they are extremely important for the survival of some bacterial pathogens.
Lipid and membrane mimetic environments modulate spin label side chain configuration in the outer membrane protein A. Flores Jiménez RH, Freed DM, Cafiso DS. J Phys Chem B. 115:14822-30 (2011).
Molecular Origin of Electron Paramagnetic Resonance Line Shapes on β-Barrel Membrane Proteins: The Local Solvation Environment Modulates Spin-Label Configuration. Freed DM, Khan AK, Horanyi PS, Cafiso DS. Biochemistry. 50:8792-803 (2011).
Synaptotagmin 1 modulates lipid acyl chain order in lipid bilayers by demixing phosphatidylserine. Lai AL, Tamm LK, Ellena JF, Cafiso DS. J Biol Chem. 286:25291-300 (2011).
Solution structure of the ESCRT-I complex by small-angle X-ray scattering, EPR, and FRET spectroscopy. Boura E, Rózycki B, Herrick DZ, Chung HS, Vecer J, Eaton WA, Cafiso DS, Hummer G, Hurley JH. Proc Natl Acad Sci U S A. 108:9437-42 (2011).
Membrane Thickness Varies Around the Circumference of the Transmembrane Protein BtuB. Ellena JF, Lackowicz P, Mongomery H, Cafiso DS. Biophys J. 100:1280-7 (2011).
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