Surface-layer protein from Caulobacter crescentus: expression, purification and X-ray crystallographic analysis

Protein surface layers are self‐assembling, paracrystalline lattices on the surface of many prokaryotes. Surface‐layer proteins have not benefited from widespread structural analysis owing to their resistance to crystallization. Here, the successful expression of a truncated version of RsaA, the surface‐layer protein from Caulobacter crescentus, from a Caulobacter protein‐expression system is reported. The purification, crystallization and initial X‐ray diffraction analysis of the truncated RsaA, the largest surface‐layer protein studied to date and the first from a Gram‐negative bacterium, are also reported. The large C‐terminal domain of the C. crescentus surface‐layer protein RsaA has been crystallized. Initial RsaA crystals have been shown to diffract to ∼2.5 Å resolution.