Structural basis for the high Ca2+ affinity of the ubiquitous SERCA2b Ca2+ pump.
Sarco(endo)plasmic reticulum Ca(2+) ATPase (SERCA) Ca(2+) transporters pump cytosolic Ca(2+) into the endoplasmic reticulum, maintaining a Ca(2+) gradient that controls vital cell functions ranging from proliferation to death. To meet the physiological demand of the cell, SERCA activity is regulated by adjusting the affinity for Ca(2+) ions. Of all SERCA isoforms, the housekeeping SERCA2b isoform displays the highest Ca(2+) affinity because of a unique C-terminal extension (2b-tail). Here, an extensive structure-function analysis of SERCA2b mutants and SERCA1a2b chimera revealed how the 2b-tail controls Ca(2+) affinity. Its transmembrane (TM) segment (TM11) and luminal extension functionally cooperate and interact with TM7/TM10 and luminal loops of SERCA2b, respectively. This stabilizes the Ca(2+)-bound E1 conformation and alters Ca(2+)-transport kinetics, which provides the rationale for the higher apparent Ca(2+) affinity. Based on our NMR structure of TM11 and guided by mutagenesis results, a structural model was developed for SERCA2b that supports the proposed 2b-tail mechanism and is reminiscent of the interaction between the alpha- and beta-subunits of Na(+),K(+)-ATPase. The 2b-tail interaction site may represent a novel target to increase the Ca(2+) affinity of malfunctioning SERCA2a in the failing heart to improve contractility.
Department of Molecular Cell Biology, Division of Biochemistry, Laboratory of Ca2+ -Transport ATPases, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.
Ilse
I
Vandecaetsbeek
Mieke
M
Trekels
Marc
M
De Maeyer
Hugo
H
Ceulemans
Eveline
E
Lescrinier
Luc
L
Raeymaekers
Frank
F
Wuytack
Peter
P
Vangheluwe
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002118:Calcium / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004795:Enzyme Stability; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
D011994:Recombinant Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium