Type
Text
Type
Thesis
Date
2007-12-01
Keywords
hydrophobic α-helices | membrane proteins | membrane-inserted hydrophobic helices
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/70844
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Hydrophobic α-helices have been widely used to study membrane protein sequencestructure relationships in model membranes. Our lab has developed fluorescence methods to determine the topography of membrane-inserted hydrophobic helices, and to understand the equilibria describing their topographic stability. Using this model membrane system, the minimum hydrophobic length necessary to form a transmembrane (TM) helix in membranes was investigated. Sequences with 13 consecutive hydrophobic residues were found to be the minimum necessary to form a predominantly TM state in a bilayer with a biologically relevant width. The ability of these short hydrophobic sequences to form TM helices in the presence of substantial negative mismatch (~10 Å) implied that lipid bilayers have a considerable ability to adjust to hydrophobic mismatch. In addition, the ability of hydrophilic residues to shift the transverse position of the TM helices within the bilayer was studied. Hydrophilic residues at some positions within iv hydrophobic helices induced transverse shifts in TM helix position such that the polar residue moved closer to the bilayer surface. The extent of shift depended on the identity of the hydrophilic residue. The shift was controlled by the combination of amino acid hydrophilicity, ionization state and the ability of the side chains to position the polar groups near the bilayer surface (snorkeling). Furthermore, the structural consequence of pathogenic hydrophilic mutations in the TM domain of neu/ErbB2 receptor was investigated. Hydrophilic mutations in the TM domain were found to alter the membrane position of the TM helix and thus redefine the transmembrane boundary. This suggested a new mode of receptor upregulation in the neu/ErbB2 oncogene. Finally, in collaboration with Dr. Eckard Wimmer, Department of Molecular Genetic and Microbiology, the membrane topography of poliovirus proteins 3A and 3AB was characterized. Fluorescence studies showed that the hydrophobic domain forms a stable TM structure in mature 3A protein, but adopts a non-TM surface topography in context of the precursor 3AB protein. The hydrophobic sequence could insert in a TM form, only when the Ctermini 3B domain was removed. Furthermore, a shortened C-terminal part of the putative hydrophobic segment (16 residues rather than 22 residues) was found to span the lipid bilayer.
Recommended Citation
Krishnakumar, Shyam S., "Sequence to Topography Relationship in Membrane-Inserted Hydrophobic Helics" (2007). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 56.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/56