Figure 36.

Conformational transition between helix-up and helix-down configurations in Syt1. (A) Ca²⁺-bound C2A domain (left) and C2B in helix-up (center) and helix-down conformations (right). (B) Potential of mean force for the transition from the helix-up to the helix-down conformation on an anionic membrane. The helix-down conformation (iii) is more stable than the helix-up conformation (i). A shallow barrier (ii) separates the two conformations. The free energy further reduces as the helix binds to the membrane surface (iv). Adapted with permission from ref (889). Copyright 2014 Biophysical Society. Published by Elsevier Inc.