Evidence for folded conformation of the cell wall protein from acetabularia (polyphysa) cliftonii

The cell wall protein from Acetabularia has a non-random structure in aqueous solution at pH 5.3, as determined on the basis of intrinsic viscosity, sedimentation velocity and small angle X-ray scattering experiments. This non-random structure is stable in a pH range of 4.5-6.8, as observed on the basis of circular dichroism and viscosity measurements, supporting that the cell wall protein has a specific folded structure. All hydrodynamic measurements, including small angle X-ray scattering in solution, in this pH range, are consistent with a prolate ellipsoid model for the shape of this protein, with overall dimensions of c = 86.0A, b = 7.0A, and a equals 7,5A, and with a radius of gyration of Rsub(g) = 39.5A. The possibility of a coiled shape was investigated using a worm-like chain model, but it was inconsistent with the experimental data. Instead, a filled particle with uniform density which is equivalent in the scattering behavior is proposed. By a comparison of the observed radius of gyration, Rsub(g) = 39.5A, and the radius of gyration of the cross section, Rsub(c) = 7.5A, we were able to describe the cell wall protein in terms of a prolate ellipsoid of revolution. Comparisons of the experimental scattering curve, plotted as log 1 (I) versus log h, with the corresponding plots of normalized intensities, calculated for particles of particular shape and various axial ratios indicate a very asymmetric shape for the cell wall protein from Acetabularia. (author)