Direct observation of Ca(2+) -induced calmodulin conformational transitions in intact Xenopus laevis oocytes by (19) F NMR spectroscopy

Abstract

The Ca(2+) -mediated conformational transition of the protein calmodulin (CaM) is essential to a variety of signal transduction pathways. Whether the transition in living cells is similar to that observed in buffer is not known. Here, we report the direct observation by (19) F NMR spectroscopy of the transition of the Ca(2+) -free and -bound forms in Xenopus laevis oocytes at different Ca(2+) levels. We find that the Ca(2+) -bound CaM population increased greatly upon binding the target protein myosin light-chain kinase (MLCK) at the same Ca(2+) level. Paramagnetic NMR spectroscopy was also exploited for the first time to obtain long-range structural constraints in cells. Our study shows that (19) F NMR spectroscopy can be used to obtain long-range structural constraints in living eukaryotic cells and paves the way for quantification of protein binding constants.

Keywords: NMR spectroscopy; calmodulin; fluorine; protein conformation; signal transduction.