IIB   20738
INSTITUTO DE INVESTIGACIONES BIOLOGICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Specific contacts between chemoreceptors and the coupling protein CheW are differentially affected during signaling
Autor/es:
PEDETTA, A; CHIAPPE, C.S.; STUDDERT, C.A.
Lugar:
Rosario
Reunión:
Congreso; IX Reunión Anual de SAMIGE (Sociedad Argentina de Microbiología General); 2013
Institución organizadora:
SAMIGE
Resumen:
Bacterial chemotaxis allows microorganisms to sense their immediate chemical environment and modulate their movement
accordingly. The main components of this signal transduction system are chemoreceptors, which sense the chemical stimuli and
control the activity of the histidine kinase CheA, within a ternary complex that also contains the adaptor protein CheW. The
activity of the kinase controls the levels of phosphorylated CheY, which communicates the sensory input to the flagellar motors.
To accomplish its function, CheW directly interacts with receptors and with CheA. The domain of CheA that interacts with CheW
(P5 domain) is homologous to CheW itself, and both domains show significant structure and sequence conservation. The
interaction of CheW with chemoreceptors occurs through a hydrophobic surface between the two beta-barrels of the protein.
CheA is proposed to interact with the receptors through the corresponding region of its P5 domain. The actual changes that
occur within the ternary complex to modulate kinase activity during signaling are still being investigated. Several models have
been proposed from structural and biochemical studies using in vitro approaches.
In order to test whether changes in the organization of the ternary complex can be detected in whole cells, we sought for specific
contacts between chemoreceptors and CheW that could be targets of disulfide crosslinking. We found pairs of cysteine
replacements that form disulfides upon treatment of whole cells with the oxidant diamide. Disulfide formation was significantly
reduced when a mutant version with altered affinity with receptors was used, indicating that crosslinking indeed reflected a
specific interaction between both proteins.
Then, we characterized the efficiency of crosslinking under different conditions. Interestingly, two different crosslinking pairs
showed opposite behavior upon attractant stimuli. This suggests the occurrence of a signal-dependent relative movement of
CheW with respect to the receptors rather than a change in the association between the two proteins. The presence/absence of
CheA in the cell also affected in opposite ways the crosslinking efficiency of these two pairs, suggesting that the P5 domain
might compete with CheW more efficiently for one of the interacting points, while favoring the interaction through the other
contact.
The obtained results are discussed under the light of current experimental evidence.