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Biophys J, August 2001, p. 884-894, Vol. 81, No. 2
and
*Skirball Institute of Biomolecular Medicine, Department of Cell
Biology, New York University School of Medicine, New York, New York;
and
Krannert Institute of Cardiology, Indiana University
Medical School, Indianapolis, Indiana USA
Phospholamban (PLB) is responsible for regulating
Ca2+ transport by Ca2+-ATPase across the
sarcoplasmic reticulum of cardiac and smooth muscle. This regulation is
coupled to
-adrenergic stimulation, and dysfunction has been
associated with end-stage heart failure. PLB appears to directly bind
to Ca2+-ATPase, thus slowing certain steps in the
Ca2+ transport cycle. We have determined 3D structures from
co-crystals of PLB with Ca2+-ATPase by cryoelectron
microscopy of tubular co-crystals at 8-10 Å resolution. Specifically,
we have used wild-type PLB, a monomeric PLB mutant (L37A), and a
pentameric PLB mutant (N27A) for co-reconstitution and have compared
resulting structures with three control structures of
Ca2+-ATPase alone. The overall molecular shape of
Ca2+-ATPase was indistinguishable in the various
reconstructions, indicating that PLB did not have any global effects on
Ca2+-ATPase conformation. Difference maps reveal densities
which we attributed to the cytoplasmic domain of PLB, though no
difference densities were seen for PLB's transmembrane helix. Based on
these difference maps, we propose that a single PLB molecule interacts with two Ca2+-ATPase molecules. Our model suggests that PLB
may resist the large domain movements associated with the catalytic
cycle, thus inhibiting turnover.
Biophys J, August 2001, p. 884-894, Vol. 81, No. 2
© 2001 by the Biophysical Society 0006-3495/01/08/884/11 $2.00
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