PMID: 30139912

Authors:

Qi X, Schmiege P, Coutavas E, Li X

Title:

Two Patched molecules engage distinct sites on Hedgehog yielding a signaling-competent complex.

Journal:

Science. 2018 Aug 23. pii: science.aas8843. doi: 10.1126/science.aas8843.

Abstract:

Aberrant Hedgehog (HH) signaling leads to various types of cancer and birth defects. N-terminally palmitoylated HH initiates signaling by binding its receptor Patched-1 (PTCH1). A recent 1:1 PTCH1-HH complex structure visualized a palmitate-mediated binding site on HH, which was inconsistent with previous studies that implied a distinct, calcium-mediated binding site for PTCH1 and HH co-receptors. Here, our 3.5-A resolution cryo-EM structure of native Sonic Hedgehog (SHH-N) in complex with PTCH1 at a physiological calcium concentration reconciles these disparate findings and demonstrates that one SHH-N molecule engages both epitopes to bind two PTCH1 receptors in an asymmetric manner. Functional assays using PTCH1 or SHH-N mutants that disrupt the individual interfaces illustrate that simultaneous engagement of both interfaces is required for efficient signaling in cells.