Dr. Karen Fleming
Associate Professor,
Biophysics

Johns Hopkins University
Dept. of Biophysics
3400 North Charles Street
Baltimore, MD 21218
410-516-7256 Office
410-516-4118 Fax
Karen.Fleming@jhu.edu
Lab Home Page

Structural and Energetic Principles of Helical Membrane Proteins

Genome sequencing efforts are revealing that perhaps as many as 20–40% of open reading frames in complex organisms may encode proteins containing at least one helical transmembrane segment. Contrasting with the approaching tidal wave of helical membrane proteins is the fact that our understanding of the sequence-structure-function relationships for membrane proteins lags far behind that of soluble proteins. This paradox emphasizes the extensive biophysical and structural work that remains to be done in the field of helical membrane proteins.

Our research is aimed at elucidating structural and energetic principles of membrane proteins. We are especially focused on understanding the structural and energetic basis of transmembrane helix-helix recognition. Our lab takes a multidisciplinary approach to address scientific questions employing molecular biology techniques, structural studies, thermodynamic investigations and computational analysis and modeling.

Currently our research projects include:

1. Structural and energetic dissection of the glycophorin A transmembrane dimer. A paradigm for transmembrane helix-helix interactions, we are probing the structural and energetic effects on dimerization of single and multiple point mutants. Our interaction studies on glycophorin A suggest the idea that specificity in helix-helix interactions for this protein may be independent of the hydrophobic environment.
2. Transmembrane interactions in SNARE fusion proteins. We are using computational modeling and thermodynamics to probe the transmembrane helix-helix interactions of synaptobrevin and other SNARE proteins. Our studies on the dimerization of synaptobrevin offer an opportunity for protein engineering and design of a membrane protein as a means to understanding its structural stability.

Selected Publications:

• Fleming, K.G., A.L. Ackerman, and D.M. Engelman. 1997. The effect of point mutations on the free energy of transmembrane alpha-helix dimerization. J. Mol. Biol. 272:266-275.
• Fleming, K.G., T.M. Hohl, R.C. Yu, S.A. Müller, B.A. Wolpensinger, A. Engel, H. Engelhardt, A.T. Brünger, T. Söllner, and P.I. Hanson. 1998. A revised model for the oligomeric state of the N-ethyl maleimide Sensitive Factor, NSF. J. Biol. Chem. 273:15675-15681.
• Schubert, C., J.A. Hirsch, V.V. Gurevich, D.M. Engelman, P.B. Sigler, and K.G. Fleming. 1999. Visual arrestin activity may be regulated by self-association. J. Biol. Chem. 274:21186-21190.
• Fleming, K.G. 2000. Riding the wave: Structural and energetic principles of helical membrane proteins. Curr. Opin. Biotechnol. (P. Hensley & D. Myszka, eds) Vol. 11:67-71.
• Fleming, K.G. 2000. Probing the Stability of Helical Transmembrane Proteins. In Energetics of Biological Macromolecules, Part C, a volume of Meth. Enzymol., ed. by M.L. Johnson and G. Ackers, 323:63-77. Academic Press.
• Fleming, K.G. and D.M. Engelman. 2001. Computation and mutagenesis suggest a right-handed structure for the synaptobrevin transmembrane dimer. Proteins, in press.
• Fleming, K.G. and DM Engelman. 2001. Specificity in transmembrane helix-helix interactions can define a hierarchy of stability for sequence variants. PNAS, in Press