The C-terminus of the TlpD cytoplasmic chemoreceptor promotes polar localization and function
Bacteria localize proteins to distinct subcellular locations, including chemoreceptors, which frequently localize to the bacterial pole. Although some polarity-promoting mechanisms have been described, many chemoreceptors lack clear routes to becoming polar. TlpD of the bacterial pathogen Helicobacter pylori is one such protein. This cytoplasmic chemoreceptor localizes to the pole in a manner that is independent of the other chemoreceptors. In this work, we evaluated the role of TlpD domains in its function. Truncated proteins were created that lacked different amounts of the N- or C-termini and expressed in H. pylori in place of native tlpD or as the sole chemoreceptor. These TlpD variants were examined for expression, protein localization, association with chemotaxis signaling proteins, and effect on motility. TlpD that lacked any portion of the N-terminal 104 amino acids did not produce detectable protein. In contrast, TlpD retained expression with loss of the C-terminal 45 amino acids. TlpD lacking the last 45 amino acids (TlpD{Delta}C4) preserved the ability to interact with CheW and CheV proteins based on bacterial two-hybrid analysis but were unable to localize to the pole either on their own or in the presence of other chemoreceptors. TlpD{Delta}C4 was found diffuse in the cytoplasm, and interacted with CheV1, CheV2, and CheV3 at this location but not CheW. TlpD{Delta}C4 did not confer chemotactic abilities in soft agar chemotaxis assays. These findings suggest the C-terminal end of TlpD plays a previously unappreciated role in promoting TlpD polar localization and function. ImportanceBacteria place their proteins in specific locations that are required for the proteins to function including the bacterial pole. How the bacterial cell identifies which proteins go to the pole is not fully understood. In this work, we dissect parts of a protein called TlpD that naturally goes to the pole. We find that mutants lacking one end of TlpD lose their polar placement, but retain other abilities. TlpD allows directed motility known as chemotaxis. This ability is critical for infection in H. pylori and numerous other pathogens. When TlpD loses its polar placement, the protein no longer functions for chemotaxis, laying the foundation for future studies that can dissect how this segment promotes function and eventually translate into therapies for H. pylori infection.