Three-Dimensional Reconstruction of E. coli SecA at Low Resolution

SecA is the essential component of the signal-peptide dependent translocation pathway in Escherichia coli (E.coli). The structure and function of SecA must be known to understand the molecular mechanism of preprotein translocation. The high flexibility of SecA causes a dynamic conformational heterogeneity which presents a barrier to the growth of crystals of high diffraction quality. Electron microscopy was used to resolve the macromolecular structure of SecA in solution by negative staining and single particle analysis at a resolution of 2.9 nm. The structure of E. coli SecA is similar to the dimeric form of Bacilius subtilis SecA and is 10 nm×10 nm×5 nm in size.