Differential CheR Affinity for Chemoreceptor C-Terminal Pentapeptides Modulates Chemotactic Responses

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Chemoreceptors in bacteria, like Escherichia coli, often feature a C-terminal pentapeptide motif.
• This pentapeptide is crucial for binding CheR and phosphorylated CheB, playing a role in chemoreceptor adaptation.
• Significant sequence variations exist among bacterial pentapeptides, and bacteria frequently possess multiple chemoreceptors with distinct pentapeptide sequences.

Purpose of the Study:

• To investigate how variations in C-terminal pentapeptide sequences affect CheR binding affinity.
• To determine the impact of pentapeptide sequence variation on bacterial chemotaxis.
• To utilize Pectobacterium atrosepticum SCRI1043, a bacterium with numerous chemoreceptors, as a model system.

Main Methods:

• Analysis of 36 chemoreceptors in Pectobacterium atrosepticum SCRI1043, focusing on 19 with C-terminal pentapeptides.
• Measurement of CheR binding affinities to various pentapeptide sequences, quantifying dissociation constants (K_D).
• Genetic manipulation involving deletion of the cheR gene and replacement of pentapeptides in the PacC chemoreceptor.

Main Results:

• CheR affinity for different pentapeptides varied up to 11-fold, with high and low affinity differing by a single amino acid.
• Deletion of the cheR gene completely abolished chemotaxis.
• Modifying the PacC pentapeptide with high or low affinity variants significantly reduced chemotaxis to L-Asp, and also affected L-Ser response, but not nitrate response.

Conclusions:

• C-terminal pentapeptide sequence variation directly influences CheR binding affinity.
• Pentapeptide alterations modulate the chemotaxis response of the cognate receptor.
• Changes in one chemoreceptor's pentapeptide can indirectly affect the chemotaxis mediated by other chemoreceptors.