Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 283, Issue 42, Pages 28305-28312Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M802743200
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Funding
- National Institutes of Health [DK57328, CA009085, RR022200, CA054174]
- PKD Foundation
- Robert J. Kleberg Jr., and Helen C. Kleberg Foundation
- National Science Foundation [TGMCB070038]
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In polycystic kidney disease (PKD), polycystin-2 (PC2) is frequently mutated or truncated in the C-terminal cytoplasmic tail (PC2-C). The currently accepted model of PC2-C consists of an EF-hand motif overlapping with a short coiled coil; however, this model fails to explain the mechanisms by which PC2 truncations C-terminal to this region lead to PKD. Moreover, direct PC2 binding to inositol 1,4,5-trisphosphate receptor, KIF3A, and TRPC1 requires residues in PC2-C outside this region. To address these discrepancies and investigate the role of PC2-C in PC2 function, we performed de novo molecular modeling and biophysical analysis. De novo molecular modeling of PC2-C using the ROBETTA server predicts two domains as follows: an EF-hand motif (PC2-EF) connected by a linker to a previously unidentified C-terminal coiled coil (PC2-CC). This model differs substantially from the current model and correlates with limited proteolysis, matrix-assisted laser desorption/ionization mass spectroscopy, N-terminal sequencing, and improved coiled coil prediction algorithms. PC2-C is elongated and oligomerizes through PC2-CC, as measured by analytical ultracentrifugation and size exclusion chromatography, whereas PC2-EF is globular and monomeric. We show that PC2-C and PC2-EF have micromolar affinity for calcium (Ca2+) by isothermal titration calorimetry and undergo Ca2+-induced conformational changes by circular dichroism. Mutation of predicted EF-hand loop residues in PC2 to alanine abolishes Ca2+ binding. Our results suggest that PC2-CC is involved in PC2 oligomerization, and PC2-EF is a Ca2+-sensitive switch. PKD-associated PC2 mutations are located in regions that may disrupt these functions, providing structural insight into how PC2 mutations lead to disease.
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