The interaction between nephrocalcin and Tamm-Horsfall proteins with calcium oxalate dihydrate

Studies of crystals of calcium oxalate dihydrate (COD) grown by vapor diffusion from solutions containing 5.1 x 10(-7), 1.5 x 10(-6), and 1.0 x 10(-5) M nephrocalcin (NC), indicate that NC profoundly affects COD's habit, size and structure. The decrease in COD size is such that at 1.0 x 10(-5) M NC, the dimensions of the crystals are reduced about five-fold with respect to those of a NC-free control. In addition, the planes of the (101) form disappear, the original habit is lost, and the diffraction pattern deteriorates to such an extent that only the 200 reflections are recorded. The results are quite different when NC is adsorbed upon rigid substrates. Under such conditions, NC acts as a promoter and not as an inhibitor of growth and thus nucleates COD from its (100) planes. Consequently, COD grows systematically juxtaposed on NC. This effect is highly reproducible and stereospecific. COD crystals grown by vapor diffusion from solutions exposed to increasing concentrations of Tamm-Horsfall protein (THP) exhibit a drastic decrease in COD's self-association. In sharp contrast with the results obtained for NC, precession photographs taken of COD samples exposed to 1.2 x 10(-5) M THP do not show evidence of deterioration of COD diffraction patterns with respect to a protein-free control. Furthermore, THP neither nucleates COD, nor does it appear to influence its growth or habit even when THP is immobilized upon a rigid substrate.