Calcium signalling Flashcards
(49 cards)
What signalling cascades are Ca2+ central to
Neuronal signalling (action potential)
Muscle contraction
Enzyme activation (CaM-kinase)
How do Ca2+ alter protein structure
Due to their charge, they can bind to negatively charged areas and alter structure and therefore function
Why must cytoplasmic calcium be kept at constant low levels
This is essential if calcium is to be used as a signal
Calcium can also form precipitates inside cells (like calcium phosphate – what makes up bones)
How are low levels of calcium maintained in the cells cytoplasm
Calcium is actively pumped out of the cytoplasm in order to maintain this
Where is calcium sequestered to
Into organelles like the ER, SR and mitochondria
What allows extracellular calcium to enter the cell
Opening of voltage gated calcium channels in response to stimuli then allows for extracellular calcium influx – this is sensed by particular proteins
What are one of the best defined mechanisms for the release of sequestered calcium
InsP3 receptor (InsPR)
What does chelate calcium refer to
specialised calcium binding proteins that have the ability to propagate the signal to the next component of the signal transduction cascade
How does calcium interact with proteins
through electrostatic interactions with EF-hand motifs (domains)
What are EF-hand motifs
looped domains and contain acidic amino acids like aspartic acid
What does aspartic acid do for the EF-hand motif
In physiological pH, the hydroxyl group of aspartic acid will dissociate and create a negative charge OH –> O- + H+
These negative charges bind to positive calcium through electrostatic interactions
What is the archetypal calcium sensor and what is it shaped like
Calmodulin
It is dumbbell shaped and consists of 2 calcium binding domains (N-domain and C-domain) - these are joined by a peptide linker
How many calciums can a signle calmodulin bind
Each calcium ion binding domain has 2 EF-hand motifs – therefore calmodulin can bind 4 calcium ions
What are the different forms of calmodulin
The unbound form is called apo-calmodulin (apo-CaM)
Bound form is calcium ion-CaM where the peptide linker forms a α-helix
What conformational change occurs when Ca2+-CaM is formed
When activated (Ca2+-CaM form) the α-helix extends which exposes a polar side and a hydrophobic side – conformational change
What does the exposed α-helix of calmodulin do
Once bound to Ca2+ the exposed α-helix can interact with a wide variety of proteins through hydrophobic and electrostatic interactions
What do hydrophobic and electrostatic interactions from the α-helix cause
This changes the structure and function of target protein (signal transduction)
How do these interactions occur on the C terminal
Interactions can occur due to charges
Where can hydrophobic interactions occur from in calmodulins structure
Hydrophobic interactions can occur around the α helix
What are the intracellular targets of calmodulin
Calmodulin has multiple intracellular protein targets
Signal transduction – CaM kinase (I and V), phosphodiesterase
Cytoskeletal – myosins, α-actin, neuroplasticity
Transcription and DNA replication – SEF-1, p62 and p68
Metabolism – phosphofructokinase
Perception – RTK’s (EFFR) and GPCR (mGLuR7)
What is an example of a target of activated calmodulin
CaM kinase
How is CaM kinase activated
Ca2+ is released into the cytoplasm in response to stimuli (signal perception) - this can be extracellular or from a sequestered store
Ca2+ binds to apo-CaM –> Ca2+-CaM
Exposed α-helix of Ca2+-CaM binds to CaM kinase activating it
What are other ways calcium can target proteins
calmodulin independent
Some proteins interact directly with Ca2+ through intrinsic EF-hand motifs
Can be seen with tropinin C
How is protein kinase C activated by Ca2+
Α, βI, βII and gamma are isoforms
They have a Ca2+ binding site in the regulatory domain
