Lene Oddershede, Henrik Flyvbjerg and Kirstine Berg-Sørensen
The motion of a single protein, a λ-receptor in the outer membrane of E. coli, is studied with optical tweezers. We present improved measurements and an analysis that accounts for stochastic errors, filters in the detection system, aliasing and hydrodynamic effects. We test a simple model for the protein's motion and find it in agreement with the low-frequency part of the data. We thus determine physical parameter values for the system with improved precision. The diffusion coefficient describing the motion of the λ-receptor is now obtained with 2% relative error for individual receptors, and varies between bacteria with roughly 70% root-mean-square deviation about the mean. This improved analysis also reveals that the simple model must be revised in order to agree with the high-frequency part of the power spectrum.
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