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Figure 1.
Interpretation of the SERCA·CPA complex. A, overall
structure of SERCA showing the N-domain (red), A-domain
(yellow), P-domain (purple), and transmembrane region (light
blue). A 2F[o] - F[c] electron density map, contoured at 1σ,
shows electron density both for AMPPCP between the N- and
A-domains and for the CPA binding site in the Ca^2+ entry
channel. The Mn^2+ ion is shown by a van der Waals sphere
representation (orange) both in the AMPPCP site and in the CPA
site. B, the AMPPCP binding site. The residues Asn^628, Arg^678,
and Lys^205 are within interacting distance of the γ-phosphate
in AMPPCP, and Asp^203 stabilizes Arg^678. Hydrogen bonding to a
water molecule (W4) is colored blue and shown as dashed lines,
whereas other hydrogen-bonding networks are colored black.
Arg^174 and Glu^439 make a salt bridge linking the A- and
N-domains. The 2F[o] - F[c] map is contoured at 1σ (blue mesh),
covering the AMPPCPC molecule. C, transmembrane domain of SERCA
with bound CPA. Three residues in the transmembrane segment of
SERCA are involved in polar interactions with CPA: Gln^56,
Asp^59, and Asn^101. Both Asn^101 and Gln^56 contribute with
side chain and backbone atoms to the coordination of the
tetramic acid part of CPA. The side chain oxygen of Gln^56
participates in the coordination sphere of the manganese atom.
The anomalous difference Fourier map (orange mesh) contoured at
10 σ identifies the Mn^2+ ion coordinated at the CPA-SERCA
binding interface. D, SERCA structures with TG-Boc12-ADT (green)
(PDB ID 2BY4) and BHQ (blue) (PDB ID 2AGV) are superimposed onto
transmembrane helices 1–5 of our new structure (PDB ID 3FGO).
TG-Boc12-ADT, BHQ, and CPA·Mn^2+ (yellow) are shown in
stick representation. The drug pocket is viewed from the
cytoplasmic side of the SR membrane. E, a structural alignment
between the Na^+, K^+-ATPase (purple) and SERCA (light blue),
both stabilized with  .
The M1 kink region of the Na^+, K^+-ATPase exhibits a
significant structural difference to SERCA. The intruding M1
loop is stabilized by Phe^93 in the Na^+,K^+-ATPase, occupying
the same binding pocket as the indole moiety of CPA and the
aromatic moiety of BHQ in SERCA.
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