NDLI: Glutamate 90 at the Luminal Ion Gate of Sarcoplasmic Reticulum Ca2+-ATPase Is Critical for Ca2+ Binding on Both Sides of the Membrane*

Content Provider	PubMed Central
Author	Clausen, Johannes D. Andersen, Jens Peter
Abstract	The roles of Ser72, Glu90, and Lys297 at the luminal ends of transmembrane helices M1, M2, and M4 of sarcoplasmic reticulum Ca2+-ATPase were examined by transient and steady-state kinetic analysis of mutants. The dependence on the luminal Ca2+ concentration of phosphorylation by Pi (“Ca2+ gradient-dependent E2P formation”) showed a reduction of the apparent affinity for luminal Ca2+ in mutants with alanine or leucine replacement of Glu90, whereas arginine replacement of Glu90 or Ser72 allowed E2P formation from Pi even at luminal Ca2+ concentrations much too small to support phosphorylation in wild type. The latter mutants further displayed a blocked dephosphorylation of E2P and an increased rate of conversion of the ADP-sensitive E1P phosphoenzyme intermediate to ADP-insensitive E2P as well as insensitivity of the E2·BeF3 − complex to luminal Ca2+. Altogether, these findings, supported by structural modeling, indicate that the E2P intermediate is stabilized in the mutants with arginine replacement of Glu90 or Ser72, because the positive charge of the arginine side chain mimics Ca2+ occupying a luminally exposed low affinity Ca2+ site of E2P, thus identifying an essential locus (a “leaving site”) on the luminal Ca2+ exit pathway. Mutants with alanine or leucine replacement of Glu90 further displayed a marked slowing of the Ca2+ binding transition as well as slowing of the dissociation of Ca2+ from Ca2 E1 back toward the cytoplasm, thus demonstrating that Glu90 is also critical for the function of the cytoplasmically exposed Ca2+ sites on the opposite side of the membrane relative to where Glu90 is located.
Related Links	http://dx.doi.org/10.1074/jbc.m110.116459
Ending Page	20792
Page Count	13
Starting Page	20780
File Format	PDF
ISSN	00219258
e-ISSN	1083351X
Journal	The Journal of Biological Chemistry
Issue Number	27
Volume Number	285
Language	English
Publisher	American Society for Biochemistry and Molecular Biology
Publisher Date	2010-07-02
Access Restriction	Open
Rights Holder	American Society for Biochemistry and Molecular Biology
Subject Keyword	Cell Biology Biochemistry Molecular Biology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Cell Biology Biochemistry Molecular Biology

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Glutamate 90 at the Luminal Ion Gate of Sarcoplasmic Reticulum Ca2+-ATPase Is Critical for Ca2+ Binding on Both Sides of the Membrane

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Glutamate 90 at the Luminal Ion Gate of Sarcoplasmic Reticulum Ca2+-ATPase Is Critical for Ca2+ Binding on Both Sides of the Membrane

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