Membrane proteins are important pharmaceutical targets and play essential roles in cells, and misfolding of membrane proteins is associated with human diseases, such as cystic fibrosis. The ability to develop therapies for membrane protein misfolding diseases is substantially limited by the lack of data on membrane protein folding and stability. In addition to the native states, we need to understand the conformations and stabilities of unfolded, partially folded, and misfolded membrane proteins. Compared to soluble proteins, whose folding has been studied for decades, the database of thermodynamic and mechanistic information on membrane protein folding is minute. Since biophysical folding studies can provide detailed access to sequence-structure- function relationships that no in vivo studies or crystal structures can provide, there is a need for additional quantitative studies of membrane proteins to better understand their physical origins. In this proposal we address this lack of information on membrane protein folding. We will study 8 outer membrane proteins, OmpX, OmpW, OmpA, PagP, OmpT, OmpLa, FadL and Omp85. Our work will double the number of unique membrane proteins whose folding has been interrogated in lipid bilayers. In the first aim, we will establish in vitro conditions under which they fold into membranes prepared from native lipid extracts. In a second aim, we will use kinetic and thermodynamic experiments employing SDS-PAGE, circular dichroism, fluorescence spectroscopy and analytical ultracentrifugation to determine the steps involved in folding and to ascertain why membrane proteins differ in their folding propensities. In the final aim we address how membrane proteins accommodate the introduction of ionizable mutations on the lipid facing surfaces of their membrane spanning regions. These experiments will provide insight into the mechanisms of how genetically-occurring ionizable group mutations cause malfunctions in human proteins.

Public Health Relevance

Little is known about the dynamical process of membrane protein folding, and human diseases occur when membrane proteins misfold. An understanding of the factors that influence membrane protein stability and membrane protein folding will find practical utility in rationalizing the effects of genetic mutations that occur in membrane proteins. This knowledge will ultimately be useful in the design of therapeutic agents to combat disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM079440-04
Application #
8274662
Study Section
Biochemistry and Biophysics of Membranes Study Section (BBM)
Program Officer
Chin, Jean
Project Start
2009-06-01
Project End
2013-12-31
Budget Start
2012-06-01
Budget End
2013-12-31
Support Year
4
Fiscal Year
2012
Total Cost
$328,804
Indirect Cost
$121,200
Name
Johns Hopkins University
Department
Physiology
Type
Schools of Arts and Sciences
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Danoff, Emily J; Fleming, Karen G (2017) Novel Kinetic Intermediates Populated along the Folding Pathway of the Transmembrane ?-Barrel OmpA. Biochemistry 56:47-60
Mo, Gary C H; Ross, Brian; Hertel, Fabian et al. (2017) Genetically encoded biosensors for visualizing live-cell biochemical activity at super-resolution. Nat Methods 14:427-434
Peterson, Janine H; Plummer, Ashlee M; Fleming, Karen G et al. (2017) Selective pressure for rapid membrane integration constrains the sequence of bacterial outer membrane proteins. Mol Microbiol 106:777-792
Marx, Dagen C; Fleming, Karen G (2017) Influence of Protein Scaffold on Side-Chain Transfer Free Energies. Biophys J 113:597-604
McDonald, Sarah K; Fleming, Karen G (2016) Aromatic Side Chain Water-to-Lipid Transfer Free Energies Show a Depth Dependence across the Membrane Normal. J Am Chem Soc 138:7946-50
Costello, Shawn M; Plummer, Ashlee M; Fleming, Patrick J et al. (2016) Dynamic periplasmic chaperone reservoir facilitates biogenesis of outer membrane proteins. Proc Natl Acad Sci U S A 113:E4794-800
Zaccai, Nathan R; Sandlin, Clifford W; Hoopes, James T et al. (2016) Deuterium Labeling Together with Contrast Variation Small-Angle Neutron Scattering Suggests How Skp Captures and Releases Unfolded Outer Membrane Proteins. Methods Enzymol 566:159-210
Fleming, Patrick J; Patel, Dhilon S; Wu, Emilia L et al. (2016) BamA POTRA Domain Interacts with a Native Lipid Membrane Surface. Biophys J 110:2698-709
McDonald, Sarah K; Fleming, Karen G (2016) Negative Charge Neutralization in the Loops and Turns of Outer Membrane Phospholipase A Impacts Folding Hysteresis at Neutral pH. Biochemistry 55:6133-6137
Plummer, Ashlee M; Fleming, Karen G (2016) From Chaperones to the Membrane with a BAM! Trends Biochem Sci 41:872-82

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