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Live Cell Calcium Imaging Combined with siRNA Mediated Gene Silencing Identifies Ca2+ Leak Channels in the ER Membrane and their Regulatory Mechanisms
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Structural basis for a pH-sensitive calcium leak across membranes.

Yanqi Chang1, Renato Bruni1, Brian Kloss1

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This study reveals the structure of a bacterial protein involved in calcium transport, showing how pH changes regulate its calcium leak activity. These findings offer insights into the function of related human proteins that protect cells from apoptosis.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Cell Biology

Background:

  • Calcium homeostasis is crucial, involving calcium leak and uptake.
  • Human Bax inhibitor-1 (hBI-1) is an antiapoptotic protein mediating calcium leak and belongs to the TMBIM family.

Purpose of the Study:

  • To determine the crystal structure of a bacterial TMBIM homolog.
  • To characterize its calcium leak activity and pH-dependent regulation.
  • To provide insights into TMBIM-mediated calcium leak and cytoprotective functions.

Main Methods:

  • X-ray crystallography to obtain protein structures.
  • Biochemical assays to characterize calcium leak activity.
  • pH-dependent functional studies in proteoliposomes.
  • Homology modeling for human TMBIM proteins.

Main Results:

  • The bacterial homolog possesses a seven-transmembrane-helix fold.
  • Structures revealed closed and open conformations interconvertible by pH.
  • A conserved aspartate pair explains pH-dependent gating.
  • Biochemical studies confirmed pH regulation of calcium influx.

Conclusions:

  • The TMBIM protein structure elucidates the mechanism of pH-gated calcium leak.
  • Understanding this bacterial homolog informs the function of human hBI-1 and TMBIM proteins.
  • This research contributes to understanding cellular calcium regulation and cytoprotection.