INVESTIGADORES
MASSAZZA diego Ariel
congresos y reuniones científicas
Título:
Trimers of dimers and the methylation response of chemoreceptors in E. coli?
Autor/es:
DIEGO A. MASSAZZA,; JOHN S. PARKINSON; CLAUDIA A. STUDDERT
Lugar:
Laughlin, Nevada,
Reunión:
Congreso; BLAST IX (Bacterial Locomotion and Signal Transduction) Meeting?; 2007
Resumen:
The chemotaxis machinery of E. coli modulates the frequency of directional changes in swimming cells through gradient-sensing receptors that govern the activity of the associated CheA kinase. An attractant increase causes rapid inhibition of CheA and a slower increase in the net methylation level of the stimulated receptor molecules, culminating in sensory adaptation and a return to pre-stimulus CheA activity upon reaching a methylation level that offsets the ligand occupancy state of the receptor population. In this study, we investigated the role that chemoreceptor trimers of dimers might play in this methylation response, using two different experimental set-ups: (1) trimer-defective Tsr molecules in cells lacking CheA and CheW (2) wild-type Tsr in cells with high levels of CheW, which disrupts trimer formation We found that several trimer defective mutants had elevated methylation levels in the absence of stimulus, as compared to wild-type Tsr. Similarly, wild-type Tsr showed an increase in unstimulated methylation level as cellular CheW level was increased. In both cases, a serine stimulus often caused a further increase in methylation level. However, some trimer defective mutants were unmethylated, and remained so after a serine stimulus, implying a serious structural disruption in the receptor dimer. Taken together, these results suggest that the formation of trimers of dimers is not essential for the methylation response to attractants. However, the assembly of chemoreceptor dimers into trimers seems to limit the accessibility of some receptor methylation sites to the methyltransferase CheR