O-Antigen plays a critical role in the bacterium-host interplay. the chain length is in important factor in O-antigen functions. Wzz protein is responsible for O-antigen chain length regulation, but the mechanism is still unknown. Here, we overexpressed the Wzz of Escherichia coli 086:H2 in wzz mutant 086:H2 strain, the yield can achieve 15 mg/L. The recombinant Wzz was purified to 99% purity in dodecylmaltoside by sequential Ni-affinity chromatography and anion-exchange. Size exclusion chromatography and in vivo cross-linking experiments both showed that Wzz formed tetramer. Furthermore. analysis with Circular dichroism revealed that the predominant structural composition in Wzz is alpha-helices, and incubation with O-antigen significantly changed Wzz conformation. The results suggested that Wzz protein can interact with O-antigen. (c) 2006 Elsevier Inc. All rights reserved.