A Calcium-Modulated Plasmonic Switch

• Published in: Journal of the American Chemical Society Vol. 130; no. 18; pp. 5836 - 5837
• Main Authors: Hall, W. Paige, Anker, Jeffrey N, Lin, Yao, Modica, Justin, Mrksich, Milan, Van Duyne, Richard P
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 07.05.2008
• Subjects: Calcium - chemistry; Calcium - metabolism; Calmodulin - chemistry; Calmodulin - metabolism; Carboxylic Ester Hydrolases - chemistry; Metal Nanoparticles - chemistry; Nanotechnology; Protein Conformation; Protein Structure, Tertiary; Silver - chemistry; Surface Plasmon Resonance - methods
• ISSN: 0002-7863; 1272-7863; 1520-5126
• DOI: 10.1021/ja7109037

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 (λmax) 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 (3σ) of 1.5 × 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.