PT  - JOURNAL ARTICLE
AU  - Brandon L. Scott
AU  - Kem A. Sochacki
AU  - Shalini T. Low-Nam
AU  - Elizabeth M. Bailey
AU  - QuocAhn Luu
AU  - Amy Hor
AU  - Andrea M. Dickey
AU  - Steve Smith
AU  - Jason G. Kerkvliet
AU  - Justin W. Taraska
AU  - Adam D. Hoppe
TI  - Membrane bending begins at any stage of clathrin-coat assembly and defines endocytic dynamics
AID  - 10.1101/163303
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 163303
4099  - http://biorxiv.org/content/early/2017/07/13/163303.short
4100  - http://biorxiv.org/content/early/2017/07/13/163303.full
AB  - Clathrin-mediated endocytosis internalizes membrane from the cell surface by reshaping flat regions of membrane into spherical vesicles(1, 2). The relationship between membrane bending and clathrin coatomer assembly has been inferred from electron microscopy and structural biology, without directly visualization of membrane bending dynamics (3–6). This has resulted in two distinct and opposing models for how clathrin bends membrane (7–10). Here, polarized Total Internal Reflection Fluorescence microscopy was improved and combined with electron microscopy, atomic force microscopy, and super-resolution imaging to measure membrane bending during endogenous clathrin and dynamin assembly in living cells. Surprisingly, and not predicted by either model, the timing of membrane bending was variable relative to clathrin assembly. Approximately half of the time, membrane bending occurs at the start of clathrin assembly, in the other half, the onset of membrane bending lags clathrin arrival, and occasionally completely assembled flat clathrin transitions into a pit. Importantly, once the membrane bends, the process proceeds to scission with similar timing. We conclude that the pathway of coatomer formation is versatile and can bend the membrane during or after the assembly of the clathrin lattice. These results highlight the heterogeneity in this fundamental biological process, and provide a more complete nanoscale view of membrane bending dynamics during endocytosis.