    4.2.1.80 | MhpD with and without Mg2+, by hanging-drop vapour-diffusion method, to 2.8 A resolution. Space group of the crystals is H3 with unit cell parameters a = 207.35 A, b = 207.35 A, c = 545.47 A, alpha = 90°, beta = 90°, and gamma = 120°. Assembles to form a 20-nm-diameter particle comprising 60 protein subunits, arranged with 532 symmetry when crystallised at low pH in the presence of phosphate or sulphate ions. Particles form rapidly and are stable in solution during gel filtration at low pH. They are probably formed through trimers of pentamers, which are stabilised by the interaction of two phosphate ions with residues of the N-terminal domains of subunits at the 3fold axis. Once the particles are formed at high concentrations of phosphate (or sulphate), they remain stable in solution at 20fold lower concentrations of the anion. Guest molecules can be trapped within the hollow protein shell during assembly. The C-termini of the subunits are freely accessible on the surface of the protein cage |
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