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Coiled-coil regions play a role in the function of the Shigella flexneri O-antigen chain length regulator Wzz_pHS2

Australian Bacterial Pathogenesis Program, Discipline of Microbiology and Immunology, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, SA 5005, Australia

Correspondence
Renato Morona
renato.morona{at}adelaide.edu.au

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.

The GenBank accession number for the sequence reported in this paper is EU220028.