Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Escherichia coli</jats:italic> group 1 K antigens form a tightly associated capsule structure on the cell surface. Although the general features of the early steps in capsular polysaccharide biosynthesis have been described, little is known about the later stages that culminate in assembly of a capsular structure on the cell surface. Group 1 capsule biosynthesis gene clusters (<jats:italic>cps</jats:italic>) in <jats:italic>E. coli</jats:italic> and <jats:italic>Klebsiella pneumoniae</jats:italic> include a conserved open reading frame, <jats:italic>wzi</jats:italic>. The <jats:italic>wzi</jats:italic> gene is the first of a block of four conserved genes (<jats:italic>wzi-wza-wzb-wzc</jats:italic>) found in all group 1 K-antigen serotypes. Unlike <jats:italic>wza</jats:italic>, <jats:italic>wzb</jats:italic>, and <jats:italic>wzc</jats:italic> homologs that are found in gene clusters responsible for production of exopolysaccharides (i.e., predominantly cell-free polymer) in a range of bacteria, <jats:italic>wzi</jats:italic> is found only in systems that assemble capsular polysaccharides. The predicted Wzi protein shows no similarity to any other known proteins in the databases, but computer analysis of Wzi predicted a cleavable signal sequence. Wzi was expressed with a C-terminal hexahistidine tag, purified, and used for the production of specific antibodies that facilitated localization of Wzi to the outer membrane. Circular dichroism spectroscopy indicates that Wzi consists primarily of a β-barrel structure, and dynamic light scattering studies established that the protein behaves as a monomer in solution. A nonpolar <jats:italic>wzi</jats:italic> chromosomal mutant retained a mucoid phenotype and remained sensitive to lysis by a K30-specific bacteriophage. However, the mutant showed a significant reduction in cell-bound polymer, with a corresponding increase in cell-free material. Furthermore, examination of the mutant by electron microscopy showed that it lacked a coherent capsule structure. It is proposed that the Wzi protein plays a late role in capsule assembly, perhaps in the process that links high-molecular-weight capsule to the cell surface.</jats:p>

Original publication




Journal article


Journal of Bacteriology


American Society for Microbiology

Publication Date





5882 - 5890