Mechanisms of growth for protein and virus crystals.

The growth of six protein and virus crystals was investigated in situ using atomic force microscopy. Most of the crystals grew principally on steps generated by two-dimensional nucleation on surfaces though some grew by development of spiral dislocations. Apoferritin grew by a rarely encountered mechanism, normal growth, usually associated only with melt or vapour phase crystallization. Cubic crystals of satellite tobacco mosaic virus (STMV) grew, at moderate to high levels of supersaturation, by the direct addition of three-dimensional nuclei followed by their rapid normal growth and lateral expansion, a mechanism not previously described to promote controlled and reproducible crystal growth from solutions. Biological macromolecules apparently utilize a more diverse range of growth mechanisms in their crystallization than any previously studied materials.