Coiled-coil Regions Play a Role in the Function of the Shigella Flexneri O-antigen Chain Length Regulator WzzpHS2

Regulation of the length of the O-antigen (Oag) chain attached to LPS in Shigella flexneri is important for virulence and is dependent on the inner-membrane protein Wzz. A lack of high-resolution structural data for Wzz has hampered efforts so far to correlate mutations affecting function of Wzz with structure and describe a mechanism for chain length regulation. Here we have used secondary structure prediction to show that the periplasmic domain of the Wzz(pHS2) protein has three regions of significant coiled-coil (CC) potential, two of which lie within an extended helical region. We describe here the first site-directed mutagenesis study to investigate the role of individual predicted CC regions (CCRs) in Wzz function and oligomerization. We found that CCRs 2 and 3 are necessary for wild-type Oag chain length regulation by Wzz(pHS2). The in vivo cross-linking profile of mutants affected in the three CCRs was not altered, indicating that individually each CCR is not required for oligomerization. Interestingly, the CCR3 mutation resulted in a temperature-sensitive phenotype and an inhibitory effect on Oag polymerization. Analysis of Wzz(pHS2) and the mutant constructs in a S. flexneri degP mutant showed that DegP did not affect the function of wild-type Wzz(pHS2) but its presence influenced the phenotype of the Wzz(pHS2) CCR3 mutant. Additionally, the phenotype of the Wzz(pHS2) CCR3 mutant was suppressed by a cis mutation near the putative cytoplasmic C-terminus of Wzz(pHS2).