Fig. 1.35 SERCA1a intramembrane Ca
2+ -binding sites. Close-up view of the two Ca
2+ -binding sites
formed by side-chain and main-chain atoms of residues belonging to the M4, M5, M6, and M8 transmembrane helices, shown in ribbon representation with key coordinating side-chain residues in sticks. Water
molecules are shown in red. The figure is based on the [Ca 2 ]E1:AMPPCP structure (pdb code 1T5S) (From
Møller et al. 2010. Reproduced with permission of Cambridge University Press).
Fig. 1.36 The Ca
2+ - and ATP-induced E2 ! E1P transition of SERCA1a (PDB structures 2C88 and
3BA6). Cartoon representations with helices M1 (orange), M2 (magenta), M3–M4 (wheat), and M5–M6
(green) shown in surface representation. In the E2 (calcium-free) state (left), the entrance to the Ca
2+ -
binding site(s) is widely open to the cytosol (arrow), due to a kink in helix M1. Binding of calcium in the
presence of a nucleotide (right) results in the occlusion of the Ca
2+ -binding sites, because the rotation of
the A domain (yellow) entails a rearrangement of the cytosolic ends of helices M1 and M3, which block the
access to the sites. The transitions ① and ② indicated refer to the scheme in Fig. 1.34 (Adapted from
Møller et al. 2010. Reproduced with permission of Cambridge University Press).
46
1 Membrane Proteins and Their Natural Environment
2+ -binding sites. Close-up view of the two Ca
2+ -binding sites
formed by side-chain and main-chain atoms of residues belonging to the M4, M5, M6, and M8 transmembrane helices, shown in ribbon representation with key coordinating side-chain residues in sticks. Water
molecules are shown in red. The figure is based on the [Ca 2 ]E1:AMPPCP structure (pdb code 1T5S) (From
Møller et al. 2010. Reproduced with permission of Cambridge University Press).
Fig. 1.36 The Ca
2+ - and ATP-induced E2 ! E1P transition of SERCA1a (PDB structures 2C88 and
3BA6). Cartoon representations with helices M1 (orange), M2 (magenta), M3–M4 (wheat), and M5–M6
(green) shown in surface representation. In the E2 (calcium-free) state (left), the entrance to the Ca
2+ -
binding site(s) is widely open to the cytosol (arrow), due to a kink in helix M1. Binding of calcium in the
presence of a nucleotide (right) results in the occlusion of the Ca
2+ -binding sites, because the rotation of
the A domain (yellow) entails a rearrangement of the cytosolic ends of helices M1 and M3, which block the
access to the sites. The transitions ① and ② indicated refer to the scheme in Fig. 1.34 (Adapted from
Møller et al. 2010. Reproduced with permission of Cambridge University Press).
46
1 Membrane Proteins and Their Natural Environment