BIOINORGANIC CHEMISTRY A Short Course Second Edition

332 GROUP I AND II METALS IN BIOLOGICAL SYSTEMS: GROUP II

atoms of residues val304 (V304), ala305 (A305), and ile307 (I307) of M4.
Figure 4 of reference 98 shows stereo diagrams of the transmembrane Ca 2+ -
binding sites. Figure 6.30 shows the coordination sphere of the two calcium
ions of the Ca 2+ - ATPase PDB: 1SU4. Table 6.10 lists selected bond distances
for the same Ca 2+ - ATPase PDB: 1SU4.
The cytoplasmic portion of Ca 2+ - ATPase, sometimes called the cytosolic
headpiece, contains three important domains. These are (1) the A (actuator or

Figure 6.30 The calcium ion coordination sphere for the Ca 2+ - ATPase as represented
by the PDB: 1SU4 X - ray crystallographic structure. Visualized using The PyMOL
Molecular Graphics System and ChemDraw Ultra, version 10.0. (Printed with permis-
sion of Delano Scientifi c, LLC and CambridgeSoft Corporation.) (See color plate)

H 2 O

Ca2+

glu309

ile307

val304

asn768 ala305

glu771

glu908

thr799

asp800 asn796

PDB: 1SU4

TABLE 6.10 Selected Bond Distances for Calcium Ions in Ca 2+ - ATPase, PDB:
1SU4

Calcium Ion Site I Calcium Ion Site II

Amino Acid Ligand
Atom

Bond Distance

to Ca 2+ ( Å )

Amino Acid Ligand

Atom Bond Distance ( Å )

Asn768, O δ 1 2.33 Val304, backbone O 2.40
Glu771, O ε 2 2.39 Ala305, backbone O 2.68
Thr799, O γ 1 2.36 Ile307, backbone O 2.32
Asp800, O δ 1 2.38 Asp800, O δ 2 2.34
Glu908, O ε 1 2.44 Asn796, O δ 1 2.22
H 2 O 1 2.29
H 2 O 2 2.30