TRIMERS OF DIMERS AND THE METHYLATION RESPONSE OF CHEMORECEPTORS IN E. COLI

DIEGO A. MASSAZZA,; JOHN S. PARKINSON; CLAUDIA A. STUDDERT

Rosario, Argentina

Congreso; XLII Reunion anual Sociedad Argentina de Investigacion en Bioquimica y Biologia Molecular; 2006

The chemical environment that surrounds E. coli cells is sensed by the periplasmic domain of chemoreceptors and the information is transmitted to the histidine kinase CheA, whose activity ultimately determines the frequency with which cells change their swimming direction to seek for optimal environments. An increase in attractant concentration results in a rapid inhibition of CheA while, at the same time, the methylation rate of receptors is increased. This latter effect, together with a reduced rate of demethylation, determines a higher level of receptor methylation and thus a return of CheA activity to its prestimulus level. We are interested in the role that the trimer-ofdimer organization of chemoreceptors plays in signaling. We address now the effect that trimers of dimers play in the methylation response specifically. To that end, we analyzed the methylation changes that occur upon addition of attractants and repellents in wild type receptors under conditions of trimer disruption, as well as the response of receptor mutants that have defects in trimer formation. We observed an increase in the level of basal methylation in ?trimer-less? conditions. In response to attractants the methylation is slightly increased under these conditions, suggesting that trimers of dimers are not essential for the communication of the occupancy state of receptors to the methylation machinery.