PhD: University of Michigan
Postdoctoral training: Caltech and University of Illinois at Urbana-Champaign
Inhibitory Serpins Folding & Function
Inhibitory serpins regulate serine and cysteine proteases involved in inflammation, immune responses and blood clotting. The unique serpin inhibitory mechanism requires formation of a covalent bond between the protease and serpin, translocation of the protease relative to the serpin, remodeling of the serpin structure and deformation of the protease structure as shown at right. In essence, inhibitory serpins behave as molecular mousetraps storing energy in their metastable native states and using that stored energy to deform and thus inhibit target proteases via a suicide mechanism. We are using single molecule fluorescence to investigate both serpin-protease interactions and how serpins, particularly alpha1-proteinase inhibitor (alpha1PI also known as alph1-antitrypsin), fold to a metastable state that is not the global minimum. We are also investigating the structures of polymers that form when alpha1PI misfolds using both fluorescence techniques and, in collaboration with Dr. Chris W.M. Kay at University College London, site-directed spin labeling and electron paramagnetic resonance (EPR).
Protein folding in the Endoplasmic Reticulum (ER)
In cells, proteins can fold vectorially (from the N to the C terminus) as they are being synthesized, and folding may be assisted by molecular chaperones. Protein folding in vivo is also complicated by the myriad of other macromolecules (>100 mg/ml) in the cell, reducing the space available to the folding protein resulting in many possible non-specific interactions. Thus, protein folding in the cell may be quite different than folding in the dilute solutions encountered in test tubes. In collaboration with Professors Lila Gierasch and Dan Hebert at the University of Massachusetts Amherst, we are extending our single molecule studies of secretory protein folding into the native folding environment, the endoplasmic reticulum.
Fluorescence microscope image of isolated ERs. The blowup of a single ER shows how Förster resonance energy transfer, FRET, (green and red fluorophores) is used to monitor the structure of a protein (blue chain) while it is synthesized and folds in the ER.
Peripheral Membrane Proteins and Membrane Binding
Mammalian phospholipases are involved in a number of important signaling cascades, and some bacterial phospholipases are also virulence factors. Phospholipase function depends on transient interactions with target membranes, and we are particularly interested in how the affinity for membranes and the kinetics of binding depend on the lipid composition as well as how mutations affect membrane binding and activity. In collaboration with Professor Mary F. Roberts at Boston College we are using fluorescence correlation spectroscopy (FCS), a "small number of molecules" technique, as well as single molecule fluorescence microscopy to investigate how phospholipases interact with lipid membranes.
Bacillus Phosphatidylinositol-specific Phospholipase C (PI-PLC)
Vesicle binding slows PI-PLC translational diffusion shifting the fluorescence correlation curves to longer times.
Grauffel, C, Yang, B, He, T, Roberts, MF, Gershenson, A & Reuter, N (Epub ahead of print) Cation-pi interactions as lipid specific anchors for phosphatidylinositol-specific phospholipase-C. J Am Chem Soc. [PubMed]
Cheng, J, Karri, S, Grauffel, C, Wang, F, Reuter, N, Roberts, MF, Wintrode, PL & Gershenson, A (2013) Does changing the predicted dynamics of a phospholipase C alter activity and membrane binding? Biophys J. 104: 185-195. [PubMed]
Gershenson A & Gierasch LM (2011) Protein folding in the cell: challenges and progress. Curr Opin Struct Biol 21: 32-41. [PubMed]
Pu, M., Roberts, M.F. & Gershenson, A. (2009) Fluorescence correlation spectroscopy of phosphatidylinositol-specific phospholipase C monitors the interplay of substrate and activator lipid binding. Biochemistry 48: 6835-6845. [PubMed]
Lu, L., Mushero, N., Hedstrom, L. & Gershenson, A. (2007) Short-lived protease serpin complexes: partial disruption of the rat trypsin active site. Protein Sci 16: 2403-2411. [PubMed]
Farbman, M.E., Gershenson, A. & Licht, S. (2007) Single-molecule analysis of nucleotide-dependent substrate binding by the protein unfoldase ClpA. J Am Chem Soc 129: 12378-12379. [PubMed]
Lu, L., Mushero, N., Hedstrom, L. & Gershenson, A. (2006) Conformational distributions of protease-serpin complexes: a partially translocated complex. Biochemistry 45: 10865-10872. [PubMed]