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The energetics and ion coupling of cholesterol transport through Patched1

T Bertie Ansell1, Robin A Corey1,2, Lucrezia Vittoria Viti3

  • 1Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.

Science Advances
|August 23, 2023
PubMed

Insights

Patched1 (PTCH1) protein regulates Hedgehog signaling by controlling cholesterol transport. Molecular simulations reveal ion coupling mechanisms for cholesterol export, clarifying PTCH1

Area of Science:

  • Molecular Biology
  • Biophysics
  • Biochemistry

Background:

  • Patched1 (PTCH1) is a tumor suppressor in the Hedgehog (HH) signaling pathway, crucial for development and tissue maintenance.
  • PTCH1's inhibition of Smoothened (SMO) is linked to ciliary cholesterol regulation, though the exact mechanism remains unclear.

Purpose of the Study:

  • To elucidate the molecular mechanism and energetics of cholesterol transport mediated by PTCH1.
  • To investigate the role of ion coupling in PTCH1-mediated cholesterol export.

Main Methods:

  • Extensive molecular dynamics (MD) simulations and free energy calculations to model cholesterol transport through PTCH1.
  • In vivo biochemical assays using PTCH1 mutants to correlate cation binding, transmembrane motion, and protein activity.
  • Complementary MD simulations of Dispatched1 to analyze conformational state transitions.

Main Results:

  • An energetic barrier of 15-20 kJ/mol was identified for cholesterol export via PTCH1.
  • Coupling of 1-3 Na+ or 2-3 K+ ions was found to facilitate cholesterol export.
  • Distinct transport states of PTCH1 were characterized, with Na+-induced transitions observed in Dispatched1.

Conclusions:

  • The study provides the first molecular description of PTCH1 transport states and their transitions.
  • Ion stoichiometry for PTCH1-mediated cholesterol export is elucidated, revealing 1-3 Na+ or 2-3 K+ involvement.
  • Findings offer insights into the energetics and ion coupling mechanisms governing PTCH1 function in Hedgehog signaling.

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