Term
| a m...... is a conserved amino acid sequence alignment: it is a local alignment corresponding to a region whose f............ or s........... is known, or its significance may be unknown |
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Definition
| motif, function, structure |
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Term
| the EF hand is a protein motif that is associated with the binding of which divalent cation? |
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Definition
ca2+
it was named from the ca2+ binding site that occurs between the E and the F alpha helices in parvalbumin |
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Term
| what configuration is the EF hand characyerised by? |
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Definition
HELIX-LOOP-HELIX configuration.
the motif is thought to resemble a clenched right hand. there are >150 EF hand containing proteins. Members of this superfamily are found soley in the cytosol |
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Term
EF hands bind calcium with an affinity of
KD ~ 10-6 M
in the presence of 3mM mg2+
what is Kd? |
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Definition
| it is the disassociation constant where 50% of molecules are actively bound. |
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Term
| what is the extracellular, intracellular (unstimulated) and intracellular (stimulated) levels of calcium? |
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Definition
extracellular 10-3
intracellular (unstimulated) 10-7
intracellular (stimulated) 10-5/-6 |
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Term
| what does the presence of a glycine at position 15 and isoleucine at position 17 of the EF loop permit? |
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Definition
glycine at position 15 permits a sharp bend in the loop
isoleucine at position 17 attaches the lop to the hydrophobic core of the molecule. |
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Term
how many residues does the EF hand contain?
which amino acid is found in position 1 of the first alpha helix? |
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Definition
29 residues.
the first alpha helix has a Glu at position 1
it also has hydrophobic residues facing the core of the molecule at postions 2,5,6, and 9 thus, the alpha helices are amphipathic |
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Term
| similarly the s....... alpha helix has a Glu at postion 21. Residues 22, 25, 26 and 29 are h............ |
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Definition
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Term
| although 6 amino acids are involved in calcium binding, there is an octahedral environment of their arrangement. How many oxygen atoms are ligands? |
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Definition
seven. Six oxygens atoms from Calmodulin and one of water
in the octahedral environment the glutamic acid at -Z acts as a bidentate ligand. The calcium is contained in a tight loop and interacts with the acidic amino acids. acidic amino acids have carboxylate oxygen ligands |
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Term
| camcium is coordinated by the side chains of f.... amino acids that can be assigned to the vertices of an octhedron. |
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Definition
five.
the sixth amino acid has calcium coordinated by a peptide carbonyl |
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Term
| to summarise the EF hand is a protein motif of 29 amino acids. |
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Definition
| its function is to bind calcium ions tightly once calcium ion levels reach around 10-6 M |
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Term
| name the calcium modulating protein that binds calcium and is almost made up entirely of EF hands? |
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Definition
Calmodulin
changes in the intracellular calcium ions are important signals in all eukaryotic cells |
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Term
| calcium2+ is an important s............. m............ involved in muscle contration. it controls the release of h........... and n............. It is involved in binding of carbohydrates by l........... Many ca2+ binding proteins have a common structural motif known as the EF hand. This motif is formed from t.... helices linked by a turn |
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Definition
| second messenger, hormones, nuerotransmitters, lectin, two |
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Term
how many EF hands does calmodulin contain?
what is the Mr of calmodulin? |
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Definition
it contains 4 EF hands
it is a 17kDa protein with a highly conseved amino acid sequence.
the KD of calmodulin is about ~10-6 M |
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Term
| why does calmodulin need calcium to be bound to it? |
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Definition
so it can bind to and activate various kinases. these are molecules that add phosphate groups to other molecules.
the resting intracellular calcium level is 10-7 M but when Calcium is acting as a second messenger, the conc rises briefly to between 10-6 M and 10-5 M |
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Term
what kind of shape does a calmodulin protein have?
what structure seperates the N-terminal from the C-terminal? |
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Definition
a dumbell shape.
the N-terminal domain has 2 EF hands seperated from a similar C-terminal domain by a unique 6-turn single alpha helix. |
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Term
what does calcium binding trigger in calmodulin?
what sort of patch is exposed as a result of this trigger? |
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Definition
a conformational change.
when 3-4 calciums ions bind to calmodulin, a conformational change is triggered that exposes a hydrophobic patch in each globular domain. |
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Term
| the hydrophobic patch is exposed by the molecule folding at which region, amino acid and postion? |
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Definition
in the central region
amino acid: Serine
Position: 81
these hydrophobic patches can interact with other proteins |
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Term
| when binding to a target peptide what does the long helix of the dumbell do? |
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Definition
it unwinds and the two lobes of calmodulin swing round to enfold the alpha helical target.
a hydrophobic patch on each lobe of the calmodulin contacts the hydrophobic side of the helical target peptide. Thus, the target peptide sits in a hydrophobic channel.
it can only do this with the shape that happens as a result of calcium binding. |
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Term
| target enzymes for calmodulin include Phosphorylase kinase, myosin light chain kinase, adenylate cyclases and the Ca2+ ATP-ase |
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Definition
Target enzymes have a mixture of basic and hydrophobic amino acids which are capable of adopting an alpha helix.
Calmodulin is a sensor of rises in intracellular calcium and calcium enhances its affinity for a number of important regulatory proteins. the calcium/calmodulin system is part of a signal transduction pathway. |
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