Ca2+ -dependent conformational changes in a C-terminal cytosolic domain of polycystin-2

Abstract

The PKD1 and PKD2 genes are the genes that are mutated in patients suffering from autosomal dominant polycystic kidney disease. The human PKD2 gene codes for a 968-amino acid long membrane protein called polycystin-2 that represents a cation channel whose activity can be regulated by Ca2+ ions. By CD, fluorescence, and NMR spectroscopy, we have studied a 117-amino acid-long fragment of the cytoplasmic domain of polycystin-2, polycystin-2-(680-796) that was proposed to contain a Ca2+-binding site. NMR structure determination reveals the existence of two Ca2+-binding sites in polycystin-2-(680-796) arranged in a typical and an atypical EF-hand motif. In the absence of Ca2+ the protein forms a dimer that is dissociated by Ca2+ binding. This dissociation may be related to the Ca2+ inactivation observed earlier. The calcium affinity of the protein was determined by fluorescence and NMR spectroscopy. At 293 K, the KD values for the high and low affinity sites are 55 μM and 179 μM, respectively. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.