SERCA
PDB file 1EUL
Ca++-ATPase from rabbit muscle sarcoplasmic reticulum. Structure determined by M. Nakasako, C. Toyoshima, H. Nomura, & H. Ogawa in 2000.Suggested display options:
Display as cartoon, and color structure.
Identify the intra-membrane segment consisting of
10 transmembrane a-helices.
Select hetero-ligand, display as spacefill, and color CPK to see the 2 Ca++ ions.
The energy barrier for entry of Ca++ into the hydrophobic membrane
interior is mitigated by formation of ion pairs with negatively charged residues
in the Ca++ binding site.
To visualize the Ca++-binding domains, type into the command
line: select 304-309,
768-771, 796-800, 908.
Enter, and then
choose display ball & stick
and color CPK.
Hold down the shift to zoom
in.
Question:
What types of amino acids and which atoms in their side-chains interact with Ca++?
Note that if you click on an amino acid it will be identified below the
command line.
The consensus sequence for all P-class pumps is residues 351-357,
which is part of the cytosolic domain. Use the command line to select these residues
and change their display to sticks.
Identify
the carboxyl in aspartate residue 351
(color CPK) that is subject to
phosphorylation.
Question: Is the active site that includes Asp351 close to the Ca++
binding sites?
Transmembrane helix #1 (numbered from the N-terminus), consisting of
residues 49-75, changes position and
conformation substantially as accessibility of the Ca++ binding site
shifts from the cytosol to the ER lumen.
Note how this helix is attached to a part of
the cytosolic domain referred to as the actuator, because of its role in
transmitting
conformational changes to the membrane domain.
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Notes
on Membrane Transport
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