Dynamics of membrane tubulation coupled with fission by a two-component module revealed on polymer cushioned bilayer islands

Abstract

Membrane tubulation coupled with fission (MTCF) is a widespread cellular phenomenon but mechanisms for their coordination remain unclear. This is partly because of the lack of assays to monitor dynamics of membrane tubulation. Using polymer cushioned bilayer islands, we analyze functions of the membrane tubulator Bridging Integrator 1 (BIN1) mixed with the fission catalyst dynamin2 (Dyn2). Our results reveal that this mixture constitutes a minimal two-component module that demonstrates MTCF. MTCF is an emergent property and arises because BIN1 dually functions in facilitating peripheral recruitment while inhibiting membrane binding of Dyn2 in a dose-dependent manner. MTCF is therefore apparent only at high Dyn2 to BIN1 ratios. Because of their mutual involvement in T-tubules biogenesis, mutations in BIN1 and Dyn2 are associated with centronuclear myopathies (CNM) and our analysis links the pathology with aberrant MTCF. Together, our results establish cushioned bilayer islands as a facile template for the quantitative analysis of membrane tubulation and inform of mechanisms that coordinate MTCF.