title: A calcium-modulated plasmonic switch.
abstract: A plasmonic switch based on the calcium-induced conformational changes of calmodulin is shown to exhibit reversible wavelength modulations in response to changing calcium concentration. The extinction maximum (lambdamax) of a localized surface plasmon resonance (LSPR) sensor functionalized with a novel calmodulin construct, cutinase-calmodulin-cutinase (CutCaMCut), reversibly shifts by 2-3 nm. A high-resolution (HR) LSPR spectrometer with a wavelength resolution (3sigma) of 1.5 x 10-2 nm was developed to detect these wavelength modulations in real-time, providing information about the dynamics and structure of the protein. The rate of conversion from open (Ca2+-bound) to closed (Ca2+-free) calmodulin is shown to be 4-fold faster than the reverse process, with a closing rate of 0.127 s-1 and opening rate of 0.034 s-1. As far as we are aware, this plasmonic switch marks the first use of LSPR spectroscopy to detect reversible conformational changes in an unlabeled protein.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: W Paige
authors.initials: WP
authors.lastname: Hall
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Anker
authors.forename: Yao
authors.initials: Y
authors.lastname: Lin
authors.forename: Justin
authors.initials: J
authors.lastname: Modica
authors.forename: Milan
authors.initials: M
authors.lastname: Mrksich
authors.forename: Richard P
authors.initials: RP
authors.lastname: Van Duyne
mesh_terms: D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry; D036103:Nanotechnology; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012834:Silver / Q000737:chemistry; D020349:Surface Plasmon Resonance / Q000379:methods
chemical_list: D002147:Calmodulin; D012834:Silver; D002265:Carboxylic Ester Hydrolases; C019952:cutinase; D002118:Calcium