The role of protein constriction in the fission of membrane tubes*

Membrane remodeling, such as fusion and fission, is involved in a variety of basic, cellular processes. When unaided, the free energy barriers for such remodeling can be prohibitively high, so biological systems employ proteins as catalysts. This work investigates the influence of proteins, such as dynamin, which constrict membrane tubes in order to lower the barrier to fission. We employ self-consistent field theory and utilize the string method to find the Minimum Free Energy Path (MFEP) in order to determine the most likely pathway for the transition. During fission, the tube first partially collapses into a worm-like micelle, which then ruptures, resulting in two capped tubes. The free energy barrier to fission depends strongly on membrane tension. Simply constricting the membrane aids the initial partial collapse, however dynamin also inserts its PH domains between head groups, distorting the membrane. Our results suggest that this distortion plays a critical role in reducing the free energy barrier to fission.