Cell biology – Mathematics – Signal transduction by molecular
switches
S-shaped signal transfer characteristics display a smaller “uncertainty
domain”
• Incoming signal that controls the switch
• Output signal coming from the switch
The total number of signal protein molecules is constant, so these fractions are
each other mirrors.
Phosphorylation happens by protein kinase.
Ideal switching behavior;
Below the threshold (drempel) of the incoming signal there is no phosphorylated
signal protein.
Above the threshold of the incoming signal all molecules are phosphorylated
This acts as a switch; whose area is very small.
S-shaped signal in/out characteristic; ultra-sensitivity
Michealis-Mention hyperbola; this one does not act as switch.
The threshold value starts at 0 which means that this switch already starts signaling
at the slightest input signal. It works like a dimmer.
Different mechanisms to achieve an ultrasensitive characteristic
• Cooperativity; cooperativity in a protein give rise to an S-shaped curve. (For
example. The amount of oxygen bound to hemoglobin)
• Decoy phosphorylation; Signal proteins contain multiply phosphorylation sites.
o Decoy (lokken) site; high affinity; phosphorylated by kinases
o Signaling site; low affinity for kinase; only phosphorylated at high signal
strength, low affinity for kinase.
• Multisite phosphorylation; Signal proteins contain multiply phosphorylation
sites, protein only gives a signal when multiple phosphorylation sites contain a
phosphate. For example, when there are 2 phosphorylation sites, with low
kinase activity and low incoming signal only one of the two will be
phosphorylated. The signal protein will not be activated. Only at high kinase
switches
S-shaped signal transfer characteristics display a smaller “uncertainty
domain”
• Incoming signal that controls the switch
• Output signal coming from the switch
The total number of signal protein molecules is constant, so these fractions are
each other mirrors.
Phosphorylation happens by protein kinase.
Ideal switching behavior;
Below the threshold (drempel) of the incoming signal there is no phosphorylated
signal protein.
Above the threshold of the incoming signal all molecules are phosphorylated
This acts as a switch; whose area is very small.
S-shaped signal in/out characteristic; ultra-sensitivity
Michealis-Mention hyperbola; this one does not act as switch.
The threshold value starts at 0 which means that this switch already starts signaling
at the slightest input signal. It works like a dimmer.
Different mechanisms to achieve an ultrasensitive characteristic
• Cooperativity; cooperativity in a protein give rise to an S-shaped curve. (For
example. The amount of oxygen bound to hemoglobin)
• Decoy phosphorylation; Signal proteins contain multiply phosphorylation sites.
o Decoy (lokken) site; high affinity; phosphorylated by kinases
o Signaling site; low affinity for kinase; only phosphorylated at high signal
strength, low affinity for kinase.
• Multisite phosphorylation; Signal proteins contain multiply phosphorylation
sites, protein only gives a signal when multiple phosphorylation sites contain a
phosphate. For example, when there are 2 phosphorylation sites, with low
kinase activity and low incoming signal only one of the two will be
phosphorylated. The signal protein will not be activated. Only at high kinase
