Calmodulin

• what is the protein motif associated with calcium binding?

  EF hand
• how was EF hand named?

  from the ca2+ binding site occuring between the E and F alpha helices in parvalbumin
• What characterises the EF hand?

  Helix-loop-helix
• what is a motif?

  A conserved amino acid sequence alignment: it is a local alignment corresponding to a region whose function or structure is known, or its significance may be unknown
• what is kd?


  Specifically that it is a measure of the affinity between 2 molecules
• what is the equation of Kd

  
• what is Kd measured in?

  M
• what occurs if the affinity of ligand for receptor is very high?

  Then k1 is high and k2 low
• what does it mean when kd is low?

  affinity for receptor is very high
• what does it mean if the kd is high?

  the affinity of the ligand for the receptor is very low
• what occurs when ligand concentration is above kd?

  most of the ligand is bound to the receptor
• what is km for?

  enzymes
• what is kd?

  The concentration at which 50% of the ligand is free and 50% is bound to receptor
• what occurs when ligand concentration is below the kd?

  Most of the ligand is free
• where are EF hands found?

  solely in the cytosol
• when do EF hand s bind to calcium?

  kd ~ 10^6
• What occurs during stimulation?

  ca2+ concentration rises to reach the EF hand kd and so is now bound by EF- hand containing protein
• why do cells keep a lower concentration of intracellular calcium?

  calcium can be toxic, and too much stimulation may lead to cell death
• how does calcium bind?

  binds to binding residue from acidic amino acids have carboxylate oxygen ligands
• how many residues does an EF hand contain?

  29
• what does Glycine allow?

  Sharp bend due to the small side chain
• what doe aspartate and glutamate allow?

  Acidic amino acids have carboxylate oxygen atoms that ligate calcium
• can EF hand bind calcium tightly?

  no, requires high concentration to keep ca2+
• what is calmodulin?

  calcium modulated protein
• how big is calmodulin?

  17kDa
• how many EF hands are in calmodulin?

  4
• what can calmodulin activate?

  kinases, as it changes shape and binds to it
• does calmodulin change based on organism?

  No, it is highly conserved
• what is the role of calcium?

  secondary messenger in muscle contraction
• what is calmodulin involved in?

  binding of carbohydrate by lectins
• what is the structure of calmodulin?

  Dumbbel shape, N and C terminal domains each have 2 EF hands, separated by a unique 6-turn single alpha helix
• what does an EF hand pair with?

  globular domains and there is cooperative calcium binding
• what is the apo structure?


  missing its ligand or binding partner
• what does the binding of calcium do to calmodulin?

  causes a conformational shape change
• what happens to calmodulin when 4 calcium ions bind?

  Triggers a conformation change which exposes a hydrophobic patch in each globular domain
• what can hydrophobic patches bind to?

  target peptides
• How does the calmodulin bind to the target peptide?

  The long helix of the dumbbel unwinds and the two lobes of calmodulin swings around to enfold the alpha helical target peptide,

  A hydrophobic patch on each lobe of the calmodulin contacts the hydrophobic side of the helical target peptide

  THE TARGET PEPTIDE SITS IN THE A HYDROPHOBIC CHANNEL
• what are some target enzyme of calmodulin?

  Phosphorylase kinase, myosin light chain kinase, adenylate cyclases and the Ca2+ ATP-ase.
• what do target peptides have to have to bind to calmodulin?

  Alpha helix
• what is calmodulin?

  a sensory of an increase in intracellular calcuim