Helicobacter pylori FlhB Function: the FlhB C-Terminal Homologue HP1575 Acts as a “Spare Part” To Permit Flagellar Export When the HP0770 FlhB _CC Domain Is Deleted

Abstract

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.

Protein Export According to Schedule: Architecture, Assembly, and Regulation of Type III Secretion Systems from Plant- and Animal-Pathogenic Bacteria

“…The C-terminal cleavage products probably remain associated with the membrane-associated portions of the proteins. Since the motility of a flagellar flhB CC mutant, which lacks the C-terminal cleavage product of FlhB, can be restored partially upon ectopic expression of flhB CC , it was suggested that the cleavage product can be provided in trans and that the cleavage event per se is not crucial for protein function (381,583). Similar findings were observed for an X. campestris pv.…”

Functional Analysis of theHelicobacter pyloriFlagellar Switch Proteins

“…Additionally, because a loss of flagellar switch proteins can feed back onto the transcription of other flagellar genes, it is hard to separate transcriptional from posttranscriptional effects. Another possibility is that either FliN domain could be acting as a molecular "spare part" reminiscent of the flhB homolog HP1575, which can compensate for the loss of only the C-terminal domain of flhB (51).…”

The FliK protein and flagellar hook‐length control

“…Whole genome array profiling of flagellar mutants has successfully identified additional genes involved in flagellar biosynthetic pathways (Niehus et al 2004;Wang et al 2006) and a similar approach could be used with a FliK mutant to further expand the class II and III regulons. There are almost certainly more general, as well as species-specific proteins involved in flagella biogenesis that have not yet been identified, a point illustrated by the recent identification of HP1575 as a so-called ''spare part,'' which can partially replace FlhB in H. pylori (Wand et al 2006). Moreover the FlhD 2 C 2 master regulon continues to grow as novel promoter binding and gene array experiments have identified other genes (some flagellar some metabolic) under the control of this regulator (Pruss et al 2003;Kapatral et al 2004;Stafford et al 2005).…”