The pilus-retraction protein PilT: ultrastructure of the biological assembly (original) (raw)

PilT is a biological motor required for the retraction of bacterial type IV pili. Nesseria gonorrhoeae PilT has been purified and its ultrastructure has been examined by freeze-etch electron microscopy, revealing a 115 Å outer diameter, 15−35 Å inner diameter ring. Aquifex aeolicus PilT crystals were obtained in a primitive hexagonal space group (unit-cell parameters a = b = 107.3, c = 68.5 Å) and diffract to a minimum Bragg spacing of 2.8 Å when PilT is co-crystallized with adenine nucleotides. Initial phases to 3.5 Å resolution have been determined by multiwavelength anomalous dispersion and density modification. Resulting electron-density maps show a hexameric A. aeolicus PilT ring 105 Å wide by 55 Å high, with an inner cavity that varies in shape and width from 20 to 40 Å over the height of the complex. Both PilT ultrastructures are very similar to type II and type IV secretion ATPases in overall shape, size and assembly.