Berlin 2015 – scientific programme

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BP: Fachverband Biologische Physik

BP 52: Protein structure and dynamics II

BP 52.4: Talk

Friday, March 20, 2015, 10:45–11:00, H 1028

Conformational Change of the Neuronal Calcium Sensor GCAP1 — •Jörg Robin, Jens Brauer, Stefan Sulmann, Christoph Lienau, and Karl-Wilhelm Koch — Carl von Ossietzky Universität, 26129 Oldenburg

The ability of photoreceptor cells to adjust to changing light conditions on a millisecond timescale relies on a well balanced interplay of two second messengers, cGMP and calcium [1]. Upon decrease of intracellular calcium due to closure of cGMP gated ion channels the guanylate cyclase is stimulated to replenish cGMP. Two sensor proteins, GCAP1 and GCAP2, regulate the activity of the guanylate cyclase in a sequential step by step order mechanism [2] by conformational change due to binding of calcium. This conformational change has recently been investigated by time-resolved fluorescence spectroscopy for GCAP2 [3]. In this study, we have site-specifically labelled each cysteine residue in GCAP1 mutants by the fluorescent dye Alexa647 and probed its local environment via time-resolved fluorescence spectroscopy. We have observed both an increase in fluorescence lifetime and in rotational correlation time for the apo compared to the calcium bound state. Our findings are supported by analysing the motional restriction of the dye in a wobbling-in-a-cone model and by molecular dynamics simulations. In conclusion, GCAP1 undergoes conformational change, but distinctly different from GCAP2. [1] Pugh, E. N. Jr. & Lamb, T. D. Handb. Biol. Phys. 3, 183 (2000) [2] Koch, K-W. & Dell'Orco, D. ACS Chem. Neurosci. 4, 909 (2013) [3] Kollmann, H. et al. ACS Chem. Biol. 7, 1006 (2012)