Heat shock response is a stress response to temperature changes and a
consecutive increase in amounts of unfolded proteins. To restore homeostasis,
cells upregulate chaperones facilitating protein folding by means of
transcription factors (TF). We here investigate two heat shock systems: one
characteristic to gram negative bacteria, mediated by transcriptional activator
sigma32 in E. coli, and another characteristic to gram positive bacteria,
mediated by transcriptional repressor HrcA in L. lactis. We construct simple
mathematical model of the two systems focusing on the negative feedbacks, where
free chaperons suppress sigma32 activation in the former, while they activate
HrcA repression in the latter. We demonstrate that both systems, in spite of
the difference at the TF regulation level, are capable of showing very similar
heat shock dynamics. We find that differences in regulation impose distinct
constrains on chaperone-TF binding affinities: the binding constant of free
sigma32 to chaperon DnaK, known to be in 100 nM range, set the lower limit of
amount of free chaperon that the system can sense the change at the heat shock,
while the binding affinity of HrcA to chaperon GroE set the upper limit and
have to be rather large extending into the micromolar range.Comment: 17 pages, 5 figure
