Proteins - EF-Hand/Calmodulin Flashcards
EF-Hand
This is a motif of 30 amino acids folding in a helix-loop-helix structure, ressembling a right hand with index and thumb extended.
How are the two EF-hand helicies ocnnected?
Calcium binding loop which binds Ca ions through acidic residues(aspartate or glutamate_
What happens when Ca binds?
Exposes binding sites for protein/membrane interactions
How does Ca interact with acidic residues?
Form a sequence with carboxylate groups forming co-ordination complex
Motifs
Conserved amino acid sequence alignments, corresponding to a region whose function or structure is known, or its signifcance may be unknonw.
Kd(Dissociation constant)
This quantifies equilibrium between ligand(L) being free in solution and bound to a site in the protein(EL) corresponding to ligand-binding site affinity.
How can Kd be mathematically described?
Ratio of rate constants for disassociation and association of the ligand-receptor complexes.
What is the equation for kD
K2/K1 Where K2 is rate of dissociation and K1 rate of association
What does a low kD mean?
A very high receptor-ligand affinity.
What is kD used to describe?
Concentraiton at which 50% of the ligand is free and 50% bound to a receptor.
Law of Mass Action
This states that rate of a chemical reaciton is proportional to the concentration of the reacting substance.
What is the binding affinity of EF-hand for Ca?
Kd = 10^6 M
How does kD for EF-hand and ca binding affinity change?
Whether found intracelluarly(10^-3) or extracellularly (10^-7-10^-6)
Why are EF-hand rarely found extracellularly?
Calcium binding loops contain several anionic AA and cytosol has higher Ca concentration
Why are Asp and Glu anioninc?
Carboxylate groups.
Why does Ca bind anions?
Two valence electrons forming co-ordination complexes.
What is the amino acid structure of EF-hand?
29 residues with a Glu at position 1 at first alpha helix, with hydrophobic molecules facting core at 2,5,6, and 9.
What are the important amino acids in the second helix?
Glu at position 21 and hydrophobic molecules at 22,25,26 and 19
Why is Gly15 important?
Permits a sharp bend in the loop.
Why is glycine useful?
Smallest AA with a single hydrogen side hcane, allowing flexibility of protein for many conformations.
Why is position 17 Ile important?
Attahcing loop the hydrophobic core of the molecule.
Calmodulin
This is important in mediation of actions of calcium in many cellular processes.
What is the general structure of calmodulin?
Two identical globular domains, each containing two EF-hand motifs mediating interactions with Ca ions.
What is the primary sequence structure of Calmodulin?
17kDa with 75 AA
