Lecturer: Mrs. Vered Frank
Affiliation: Racah Institute of Physics,
The Hebrew University of Jerusalem
Abstract:
The clustering of membrane-bound
receptors plays an essential role in various
biological systems. A notable model
system for studying this phenomenon is
the bacterial chemosensory cluster that
allows motile bacteria to navigate along
chemical gradients in their environment.
While the basic structure of these
chemosensory clusters is becoming clear,
their dynamic nature and operation are
not yet understood. In this work we
focused on chemoreceptor clusters of the
bacterium E. coli. First, we provide
evidence for stimulus-induced dynamics
in these sensory clusters. We found that
when a stimulus is applied, the packing of
the receptors slowly decreases and that
the process reverses when the stimulus is
removed. Second, using specific
mutations, we created an E. coli strain
with functional but dispersed signaling
units. This allowed us to directly study
the contribution of receptor clustering to
chemotactic signaling and gradient-
tracking performance. We found that
chemoreceptor clusters were
approximately 10-fold more sensitive to
attractant stimuli than dispersed signaling
units. Furthermore, cells expressing
dispersed signaling units couldn't track
gradients emanating by diffusion from a
constant source. Analysis of such
gradients indicated that the sensitivity
gained through receptor clusters may
indeed be crucial for sensing such
sources.