Time-resolved tryptophan fluorescence anisotropy investigation of bacteriophage M13 coat protein in micelles and mixed bilayers.
Coat protein of bacteriophage M13 is examined in micelles and vesicles by time-resolved tryptophan fluorescence and anisotropy decay measurements and circular dichroism experiments. Circular dichroism indicates that the coat protein has alpha-helix (60%) and beta-structure (28%) in 700 mM sodium dodecyl sulfate micelles and predominantly beta-structure (94%) in mixed dimyristoylphosphatidylcholine/dimyristoylphosphatidic acid (80/20 w/w) small unilamellar vesicles. The fluorescence decay at 344 nm of the single tryptophan in the coat protein after excitation at 295 or 300 nm is a triple exponential. In the micelles the anisotropy decay is a double exponential. A short, temperature-independent correlation time of 0.5 +/- 0.2 ns reflects a rapid depolarization process within the coat protein. The overall rotation of the coat protein-detergent complex is observed in the decay as a longer correlation time of 9.8 +/- 0.5 ns (at 20 degrees C) and has a temperature dependence that satisfies the Stokes-Einstein relation. In vesicles at all lipid to protein molar ratios in the range from 20 to 410, the calculated order parameter is constant with a value of 0.7 +/- 0.1 from 10 to 40 degrees C, although the lipids undergo the gel to liquid-crystalline phase transition. The longer correlation time decreases gradually on increasing temperature. This effect probably arises from an increasing segmental mobility within the coat protein. The results are consistent with a model in which the coat protein has a beta-structure and the tryptophan indole rings do not experience the motion of the lipids in the bilayer because of protein-protein aggregation.
Datema
K P
KP
Department of Molecular Physics, Agricultural University, Wageningen, The Netherlands.
Visser
A J
AJ
van Hoek
A
A
Wolfs
C J
CJ
Spruijt
R B
RB
Hemminga
M A
MA
D002942:Circular Dichroism; D003090:Coliphages; D004134:Dimyristoylphosphatidylcholine; D004926:Escherichia coli; D005454:Fluorescence Polarization; D020404:Glycerophospholipids; D008051:Lipid Bilayers; D008823:Micelles; D008968:Molecular Conformation; D010712:Phosphatidic Acids; D011487:Protein Conformation; D014364:Tryptophan; D014759:Viral Envelope Proteins
D020404:Glycerophospholipids; D008051:Lipid Bilayers; D008823:Micelles; D010712:Phosphatidic Acids; D014759:Viral Envelope Proteins; C025602:dimyristoylphosphatidic acid; D014364:Tryptophan; D004134:Dimyristoylphosphatidylcholine