Price, E. ShaneAleksiejew, MarekJohnson, Carey K.2017-04-272017-04-272011-07-28Price, E. S., Aleksiejew, M., & Johnson, C. K. (2011). FRET-FCS Detection of Intra-Lobe Dynamics in Calmodulin. The Journal of Physical Chemistry. B, 115(29), 9320–9326. http://doi.org/10.1021/jp203743mhttps://hdl.handle.net/1808/23847Fluorescence correlation spectroscopy (FCS) can be coupled with Förster resonance energy transfer (FRET) to detect intramolecular dynamics of proteins on the microsecond time scale. Here we describe application of FRET-FCS to detect fluctuations within the N-terminal and C-terminal domains of the Ca2+-signaling protein calmodulin. Intramolecular fluctuations were resolved byglobal fitting of the two fluorescence autocorrelation functions (green-green and red-red) together with the two cross-correlation functions (green-red and red-green). To match the Förster radius forFRET to the dimensions of the N-terminal and C-terminal domains, a near-infrared acceptor fluorophore (Atto 740) was coupled with a green-emitting donor (Alexa Fluor 488). Fluctuations were detected in both domains on the time scale of 30 to 40 μs. In the N-terminal domain, the amplitude of the fluctuations was dependent on occupancy of Ca2+ binding sites. A high amplitude of dynamics in apo-calmodulin (in the absence of Ca2+) was nearly abolished at a high Ca2+ concentration. For the C-terminal domain the dynamic amplitude changed little with Ca2+ concentration. The Ca2+ dependence of dynamics for the N-terminal domain suggests that the fluctuations detected by FCS in the N-terminal domain are coupled to the opening and closing of the EF-hand Ca2+-binding loops.This document is the Accepted Manuscript version of a Published Work that appeared in final form in the Journal of Physical Chemistry B, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp203743m.CalmodulinFluorescence correlation spectroscopyFRETProtein dynamicsArticle10.1021/jp203743mPMC3151148openAccess