Translocation of group 1 capsular polysaccharide to the surface of Escherichia coli requires a multimeric complex in the outer membrane

Surface expression of the group 1 K30 capsular polysaccharide of Escherichi a coli strain E69 (O9a:K30) requires Wza(K30), a member of the outer membra ne auxiliary (OMA) protein family. A mutation in wza(K30) severely restrict s the formation of the K30 capsular structure on the cell surface, but does not interfere with the biosynthesis or polymerization of the K30 repeat un it. Here we show that Wza(K30) is a surface-exposed outer membrane lipoprot ein, Wza(K30) multimers form ring-like structures in the outer membrane tha t are reminiscent of the secretins of type II and III protein translocation systems. We propose that Wza(K30) forms an outer membrane pore through whi ch the K30-capsular antigen is translocated, This is the first evidence of a potential mechanism for translocation of high molecular weight polysaccha ride across the outer membrane. The broad distribution of the OMA protein f amily suggests a similar process for polysaccharide export in diverse Gram- negative bacteria.