Lecture 4 - Exam 5 Flashcards
Global regulators have the ability to ?
Regulate genes and operons that belong to different metabolic pathways.
What is a regulon?
Often a group of genes that are involved in response to an environmental stimulus. Multiple genes and/or operons regulated by the same transcriptional regulator.
There are multiple levels of gene regulation:
Transcription (most important in bacteria), post-transcription, translation, post-translation
What are the steps in environmental sensing and response?
1) Recognition of environmental stimuli
2) Transduction of information
3) Induction of response via gene expression or other mechanism.
What are the types of environmental sensing and response systems?
Two-component regulatory systems:
-major mode of environmental sensing and signal transduction mechanism in Bacteria and Archaea
-also found in some protozoa and plants but NOT found in mammals
Quorum sensing:
-bacterial communication system for coordinated gene regulation depending on cell density
-can be intraspecies and interspecies
Other mechanisms:
-alternative sigma factors/transcriptional regulators
-riboswitches
Two-component regulatory systems are ideally suited to function in the _____________.
Integration of multiple signals.
Different two component systems can process multiple signals into a particular response by ?
Interacting with one another (cross-talk or reciprocal regulation)
-and/or by phosphorylating from small molecular weight phosphodonors
Do many two-component regulatory systems exist in bacteria?
Multiple regulatory systems are constantly functioning ___________ in generalist bacteria.
Yes
simultaneously
The average number of two component regulatory systems in a bacterial genome has been estimated at around _____, with the largest number being over _____.
30;200
What kind of bacteria have a greater number of two component regulatory systems and why?
Free-living bacteria because they have to adapt to many different environmental conditions.
Why kind of bacteria have no two-component systems?
Typically these bacteria are endosymbionts or pathogens.
General model of two component regulatory systems:
Sensor = ?
Transducer = ?
Signal sensed by sensor, phosphorylation of sensor and transducer, phosphorylated transducer activates transcription.
Sensor = Histidine kinase domain to sense the extracytoplasmic environment*
Transducer = Response regulator ; usually a DNA binding protein**
All two component regulatory systems involve the sensor transmitting the signal to the response regulator, this is typically by?
Phosphorylation
When an extracellular signal is received by a histidine kinase, the signal can result in three distinct outcomes:
- Autokinase activity resulting in autophosphorylation of the HK.
- Phosphotransfer to the response regulator (often acts as a transcription factor which activates or represses a particular set of response genes)
- Phosphatase activity, leading to the dephosphorylation of the response regulator.
Two component regulator systems consist of a sensor protein (e.g. histidine kinase) that ?
Transfers a high-energy phosphoryl group to the response regulator, which is often a transcription factor.
What happens when the membrane bound sensor kinase sense a particular environmental stimulus?
-What does the kinase activity depend on?
-What happens to the phosphate group?
The conserved histidine residue (H) in the cytoplasmic sensor domain of this protein is phosphorylated.
-Depends on ATP which is bound to the catalytic domain
-The phosphate group is then transferred to the conserved aspartate residue (D) in the receiver domain of the cognate response regulator.
What are the two types of two component regulatory systems?
Sensor-Response Regulator
Phosphorelay System
Give an overview of sensor-response regulator two component system.
-The prototypical two-component system is comprised of a single sensor kinase (SK) and a single response regulator (RR)
-The input domain of the SK recognizes a specific signal from the environment.
Describe the mechanism of the sensor-response regulator system.
-The sensor kinase autophosphorylates a conserved histidine residue in the kinase domain, in response to environmental signal sensing in the sensing domain.
-The autokinase reaction uses ATP to phosphorylate a conserve His residue of the Kinase domain.
-The phosphotransfer reaction transfers the phosphoryl group from the His residue of the sensor histidine kinase (SHK) to a conserved Asp residue of the REC domain of the response regulator.
-The transfer of the high energy phosphoryl group to the conserved aspartate residue in the receiver domain of the response regulator results in enhanced DNA-binding activity.
Give an overview of the phosphorelay system.
-Phosphorelay systems are comprised of an SK and a terminal RR.
-These systems also contain an intermediate regulator (connector) lacking an output domain and a phosphotransfer protein with a conserved histidine for phosphorylation.
(other SHKS w/ intramembrane sensors and cytoplasmic sensors may also be present.
Describe the phosphorelay system.
Are more complex and involve multiple phosphorylation steps prior to producing a response.
The His-Asp-His-Asp three step phosphorelay consists of:
A. The transfer of the phosphoryl group from the conserved histidine in the sensor kinase.
B. To aspartate and histidine residues in auxiliary proteins (connector and phosphodonor)
C. Before transfer to the aspartate in the receiver domain of the response regulator.
-Added complexity provides for multiple regulatory checkpoints and points of integration between signaling pathways.
Most HKs are _______________.
and function as ____________.
Periplasmic membrane receptors.
Homodimers: autophosphorylation is a bimolecular event.
What are the domains od the HKs?
-Sensor domain: periplasmic binding domain that sense external stimuli
-Transmembrane domain: Poorly understood, but critical for sending signal to kinase domain
-Kinase domain: Histidine-containing phosphotransfer domain that is autophosphorylated upon the signal from the sensor domain being transmitted.
The response regulator is comrpised of:
A receiver domain: A conserved aspartate residue that is phosphorylated by the histidine kinase
A regulatory domain: can function as a DNA-binding transcriptional regulator, an enzymatic activator (CheB) or in protein-protein interactions (CheY).
