Ph.D. 2005, University Illinois, Urbana Champaign; Postdoc 2005-2007 University of Pennsylvania; Postdoc 2007-2011 University of Wisconsin, Madison
Honors and Awards:
IME Postdoctoral Fellow 2005-2007, NIH K99 Career Transition Award 2010-
Our research is focused on a family of proteins known as the ferlins, which help regulate membrane trafficking events and have been linked to several human pathologies. Specifically, work currently focuses on the muscle protein dysferlin, which is believed to catalyze fusion between the plasma membrane and intracellular vesicles in response to elevated calcium levels. Mutations in dysferlin have been implicated in several forms of muscular dystrophy, suggesting a key role for the protein in muscle physiology. Also of interest is otoferlin. Although still unclear, otoferlin may modulate the release of neurotransmitter and the encoding of sound in the brain. Mutations in otoferlin have been linked to deafness in human patients. We are currently characterizing both of these calcium sensing proteins in an attempt to understand the exact contributions of these proteins to membrane fusion, as well as the basis for why mutants in dysferlin and otoferlin result in muscular dystrophy and deafness.
In addition, we are also interested in ferlin binding partners, with special focus on syntaxin and SNAP-25. These transmembrane proteins are members of the SNAREs, a family of proteins involved in nearly all intracellular membrane trafficking and exocytotic events. By using a combination of biochemical, biophysical, and spectroscopic approaches, we aim to understand the conformational changes that occur within these proteins that help accelerate fusion between lipid bilayers.
Current experiments include the reconstitution of SNAREs, otoferlin and dysferlin into synthetic vesicles to study calcium triggered membrane fusion in vitro, as well as the use of fluorescence methods like FRET to monitor protein-protein and protein-lipid interactions, confocal imaging and immunofluorescence to visualize protein and lipid redistribution within cells after wounding.
In addition, collaborative efforts to determine the structure of these proteins via X-ray and NMR are also planned.
Codding, S., Abdullah, N., Marty, N., Johnson, C.P. (2015) "Dysferlin binds SNAREs and stimulates membrane fusion in a calcium dependent manner" J Biol Chem (in revision)
Chatterjee, P., Abdullah, N., LaDu, J., Tanguay, R., Johnson, C.P. (2015) “Otoferlin is necessary for balance and hearing in zebrafish” Mol Cell Biol 35:1043-54
Padmanarayana, M., Hams, N., Speight, L., Peterson, E., Mehl, R., Johnson, C.P. (2014) “Characterization of the Lipid Binding Properties of Otoferlin Reveal Specific Interactions Between PI(4,5)P2 and the C2C and C2F Domains.” Biochemistry, 53:5023-33
Abdullah, N., Mary, N., Johnson, C.P. (2014) “Isothermal titration calorimetry reveals all seven domains of dysferlin bind calcium” Biophys J. 106: 382-389
Marty, N., Abdullah, N., Johnson, C.P. (2013) “The C2 domains of otoferlin, dysferlin, and myoferlin alter the structure of lipid bilayers” Biochemistry 52: 5585-5592
Mechanism and function of synaptotagmin-mediated membrane apposition. Hui E, Gaffaney JD, Wang Z, Johnson CP, Evans CS, Chapman ER. Nat Struct Mol Biol. 2011
Otoferlin is a calcium sensor that directly regulates SNARE-mediated membrane fusion. Johnson CP, Chapman ER. J Cell Biol. 2010 191:187-97.
Synaptotagmin-mediated bending of the target membrane is a critical step in Ca(2+)-regulated fusion. Hui E, Johnson CP, Yao J, Dunning FM, Chapman ER. Cell. 2009 138: 709-21.
Forced unfolding of proteins within cells. Johnson CP, Tang HY, Carag C, Speicher DW, Discher DE. Science. 2007 Aug 317: 663-6.
Pathogenic proline mutation in the linker between spectrin repeats: disease caused by spectrin unfolding. Johnson CP, Gaetani M, Ortiz V, Bhasin N, Harper S, Gallagher PG, Speicher DW, Discher DE. Blood. 2007109:3538-43
Structural studies of the neural-cell-adhesion molecule by X-ray and neutron reflectivity. Johnson CP, Fragneto G, Konovalov O, Dubosclard V, Legrand JF, Leckband DE. Biochemistry. 2005 Jan 44:546-54.
Direct evidence that neural cell adhesion molecule (NCAM) polysialylation increases intermembrane repulsion and abrogates adhesion. Johnson CP, Fujimoto I, Rutishauser U, Leckband DE. J Biol Chem. 2005 280:137-45.
Mechanism of homophilic adhesion by the neural cell adhesion molecule: use of multiple domains and flexibility. Johnson CP, Fujimoto I, Perrin-Tricaud C, Rutishauser U, Leckband D. Proc Natl Acad Sci U S A. 2004 101:6963-8.
Engineered protein a for the orientational control of immobilized proteins. Johnson CP, Jensen IE, Prakasam A, Vijayendran R, Leckband D. Bioconjug Chem. 2003 14:974-8.
Martel. L., Johnson, C., Boutet, S., Al-Kurdi, R., Konovalov, O., Robinson, I., Leckband, D., Legrand, J-F., X-ray reflectivity investigations of two-dimensional assemblies of C-cadherins, J. Phys. IV France, 12, Pr365-Pr377, 2003
Fluorescence and 19F NMR evidence that phenylalanine, 3-L-fluorophenylalanine and 4-L-fluorophenylalanine bind to the L-leucine specific receptor of Escherichia coli. Luck LA, Johnson C. Protein Sci. 2000 9:2573-6.
Zhang, Z., Patel, R., Kothari, R., Johnson, C., Friberg, S., Aikens, P., Stable silver clusters and nanoparticles prepared in polyacrylate and inverse micellar solutions, J. Phys. Chem. B. 104, 1176-1182, 2000.