Biophysical studies of the Pf1 coat protein in the filamentous phage, in detergent micelles, and in a membrane environment.
During the assembly of the Pf1 phage, the membrane-bound coat proteins convert into subunits of the filamentous phage. Fourier-transform infrared (FT-IR) transmission spectroscopy has been applied to a study of the secondary structure of these coat proteins when present (a) in the phage, (b) in detergent micelles, and (c) in a phospholipid membrane aqueous system. Suspensions of the Pf1 phage in H2O and 2H2O show an amide I band at 1652 cm-1, indicative of a high content of the alpha-helical structure present. Oriented films of the Pf1 phage studied by polarized FT-IR transmission spectroscopy indicate that the alpha-helical structures as well as the tyrosine residues (band at 1515 cm-1) are both aligned along the axis of the phage. When the Pf1 coat protein is present in sodium dodecyl sulfate detergent micelles and in lipid membrane systems, the FT-IR spectra show an amide I band at 1657-1658 cm-1, also indicative of a predominantly alpha-helical secondary structure. H/2H amide proton exchange studies show that when present in a phospholipid membrane system some 50-60% of the Pf1 protein exchanges rapidly, while the rest undergoes slow exchange. This is consistent with a proportion of the protein being exposed to the solvent and the other being embedded in the lipid bilayer. The presence of a band at 1630-1640 cm-1 is indicative of the presence of random structures.(ABSTRACT TRUNCATED AT 250 WORDS)
Azpiazu
I
I
Department of Protein and Molecular Biology, Royal Free Hospital School of Medicine, London, United Kingdom.
Gomez-Fernandez
J C
JC
Chapman
D
D
D002152:Calorimetry, Differential Scanning / Q000379:methods; D002213:Capsid / Q000737:chemistry* / Q000302:isolation & purification; D017912:Inovirus / Q000737:chemistry*; D008823:Micelles; D011092:Polyethylene Glycols; D011550:Pseudomonas aeruginosa / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
D008823:Micelles; D011092:Polyethylene Glycols