Helicobacter pylori FlhB function: the FlhB C-terminal homologue HP1575 acts as a "spare part" to permit flagellar export when the HP0770 FlhBCC domain is deleted.

In Helicobacter pylori 26695, a gene annotated HP1575 encodes a putative protein of unknown function which shows significant similarity to part of the C-terminal domain of the flagellar export protein FlhB. In Salmonella enterica, this part (FlhB(CC)) is proteolytically cleaved from the full-length FlhB, a processing event that is required for flagellar protein export and, thus, motility. The role of FlhB (HP0770) and its C-terminal homologue HP1575 was studied in H. pylori using a range of nonpolar deletion mutants defective in HP1575, HP0770, and the CC domain of HP0770 (HP0770(CC)). Deletion of HP0770 abolished swimming motility, whereas mutants carrying a deletion of either HP1575 or HP0770(CC) retained their ability to swim. An H. pylori strain containing deletions in both HP1575 and HP0770(CC) was nonmotile and did not produce flagella, suggesting that at least one of the two proteins had to be present for flagellar assembly to occur. Indeed, motility was restored when HP1575 was reintroduced into this strain immediately downstream of, but not fused to, the truncated HP0770 gene. Thus, HP1575 can functionally replace HP0770(CC) in this background. Like FlhB in S. enterica, HP0770 appeared to be proteolytically processed at a conserved NPTH processing site. However, mutation of the proline contained within the NPTH site of HP0770 did not affect motility and flagellar assembly, although it clearly interfered with processing when the protein was heterologously produced in Escherichia coli.