Conformation and orientation of the gene 9 minor coat protein of bacteriophage M13 in phospholipid bilayers

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Abstract

The membrane-bound state of the gene 9 minor coat protein of bacteriophage M13 was studied in model membrane systems, which varied in lipid head group and lipid acyl chain composition. By using FTIR spectroscopy and subsequent band analysis a quantitative analysis of the secondary structure of the protein was obtained. The secondary structure of the gene 9 protein predominantly consists of α-helical (67%) and turn (33%) structures. The turn structure is likely to be located C-terminally where it has a function in recognizing the phage DNA during bacteriophage assembly. Attenuated total reflection FTIR spectroscopy was used to determine the orientation of gene 9 protein in the membrane, revealing that the α-helical domain is mainly transmembrane. The conformational and orientational measurements result in two models for the gene 9 protein in the membrane: a single transmembrane helix model and a two-helix model consisting of a 15 amino acid long transmembrane helix and a 10 amino acid long helix oriented parallel to the membrane plane. Potential structural consequences for both models are discussed.

Keywords

M13
Minor coat protein
Membrane protein orientation
Protein conformation
FTIR

Abbreviations

ATR-FTIR, attenuated total reflection Fourier transform infrared
CD, circular dichroism
R, dichroic ratio
DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine
DMPG, 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol
DOPC, 1,2-dioleoyl-sn-glycero-3-phosphocholine
DOPG, 1,2-dioleoyl-sn-glycero-3-phosphoglycerol
DPPC, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol
DSC, differential scanning calorimetry
FTIR, Fourier transform infrared
HPSEC, high performance size exclusion chromatography
L/P, lipid to protein molar ratio
TFA, trifluoroacetic acid
TFE, trifluoroethanol

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