Structure of the EF-hand domain of polycystin-2 suggests a mechanism for Ca2+-dependent regulation of polycystin-2 channel activity.
The C-terminal cytoplasmic tail of polycystin-2 (PC2/TRPP2), a Ca(2+)-permeable channel, is frequently mutated or truncated in autosomal dominant polycystic kidney disease. We have previously shown that this tail consists of three functional regions: an EF-hand domain (PC2-EF, 720-797), a flexible linker (798-827), and an oligomeric coiled coil domain (828-895). We found that PC2-EF binds Ca(2+) at a single site and undergoes Ca(2+)-dependent conformational changes, suggesting it is an essential element of Ca(2+)-sensitive regulation of PC2 activity. Here we describe the NMR structure and dynamics of Ca(2+)-bound PC2-EF. Human PC2-EF contains a divergent non-Ca(2+)-binding helix-loop-helix (HLH) motif packed against a canonical Ca(2+)-binding EF-hand motif. This HLH motif may have evolved from a canonical EF-hand found in invertebrate PC2 homologs. Temperature-dependent steady-state NOE experiments and NMR R(1) and R(2) relaxation rates correlate with increased molecular motion in the EF-hand, possibly due to exchange between apo and Ca(2+)-bound states, consistent with a role for PC2-EF as a Ca(2+)-sensitive regulator. Structure-based sequence conservation analysis reveals a conserved hydrophobic surface in the same region, which may mediate Ca(2+)-dependent protein interactions. We propose that Ca(2+)-sensing by PC2-EF is responsible for the cooperative nature of PC2 channel activation and inhibition. Based on our results, we present a mechanism of regulation of the Ca(2+) dependence of PC2 channel activity by PC2-EF.
Petri
Edward T
ET
Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
Celic
Andjelka
A
Kennedy
Scott D
SD
Ehrlich
Barbara E
BE
Boggon
Titus J
TJ
Hodsdon
Michael E
ME
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D017124:Conserved Sequence / Q000235:genetics; D020832:EF Hand Motifs / Q000235:genetics*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D007690:Polycystic Kidney Diseases / Q000235:genetics* / Q000378:metabolism; D011487:Protein Conformation; D017385:Sequence Homology; D050396:TRPP Cation Channels / Q000737:chemistry* / Q000378:metabolism*
D002118:Calcium; D050396:TRPP Cation Channels