Terasaki spiral ramps in the rough endoplasmic reticulum.
We present a model describing the morphology as well as the assembly of "Terasaki ramps," the recently discovered helicoidal connections linking adjacent sheets of the rough endoplasmic reticulum (ER). The fundamental unit is a localized symmetric double-ramped "parking garage" formed by two separated gently pitched, approximately helicoidal, ramps of opposite chiralities. This geometry is stabilized by a short-range repulsive interaction between ramps associated with bending energy which opposes the long-range attraction associated with tension. The ramp inner boundaries are themselves stabilized by the condensation of membrane-shaping proteins along their length. A mechanism for parking garage self-assembly is proposed involving the nucleation of dipoles at the center of tubular three-way junctions within the smooth ER. Our predictions are compared with the experimental data.
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510 México DF, Mexico.
Jemal
J
Guven
Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, California 93106-4030, USA.
Greg
G
Huber
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510 México DF, Mexico.
Dulce María
DM
Valencia
D018870:Endoplasmic Reticulum, Rough / Q000502:physiology* / Q000648:ultrastructure*; D008954:Models, Biological