Transmembrane segment enhanced labeling as a tool for the backbone assignment of alpha-helical membrane proteins.
Recent advances in cell-free expression protocols have opened a new avenue toward high-resolution structural investigations of membrane proteins by x-ray crystallography and NMR spectroscopy. One of the biggest challenges for liquid-state NMR-based structural investigations of membrane proteins is the significant peak overlap in the spectra caused by large line widths and limited chemical shift dispersion of alpha-helical proteins. Contributing to the limited chemical shift dispersion is the fact that approximately 60% of the amino acids in transmembrane regions consist of only six different amino acid types. This principle disadvantage, however, can be exploited to aid in the assignment of the backbone resonances of membrane proteins; by (15)N/(13)C-double-labeling of these six amino acid types, sequential connectivities can be obtained for large stretches of the transmembrane segments where number and length of stretches consisting exclusively of these six amino acid types are enhanced compared with the remainder of the protein. We show by experiment as well as by statistical analysis that this labeling scheme provides a large number of sequential connectivities in transmembrane regions and thus constitutes a tool for the efficient assignment of membrane protein backbone resonances.
Institute of Biophysical Chemistry and Center for Biomolecular Magnetic Resonance and Cluster of Excellence Macromolecular Complexes, University of Frankfurt, Max-von-Laue Strasse 9, 60438 Frankfurt am Main, Germany.
Sina
S
Reckel
Solmaz
S
Sobhanifar
Birgit
B
Schneider
Friederike
F
Junge
Daniel
D
Schwarz
Florian
F
Durst
Frank
F
Löhr
Peter
P
Güntert
Frank
F
Bernhard
Volker
V
Dötsch
D000595:Amino Acid Sequence; D002247:Carbon Isotopes / Q000737:chemistry; D018360:Crystallography, X-Ray; D007553:Isotope Labeling / Q000379:methods*; D008565:Membrane Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D017433:Protein Structure, Secondary
D002247:Carbon Isotopes; D008565:Membrane Proteins; D009587:Nitrogen Isotopes