Weaklings unite to reorganize cell

Although normally seen as a branching network of membranes, the endoplasmic reticulum can quickly and dramatically reorganize into a variety of regular, tightly stacked arrays. Referring to these structures collectively as organized smooth endoplasmic reticulum (OSER), Snapp et al. report on page 257 that surprisingly weak protein interactions can induce their formation. The results undermine a previous model of OSER formation, suggest a general mechanism that could drive membrane stacking in organelle biogenesis, and raise a warning flag for users of green fluorescent protein (GFP) tags.

Previous work suggested that OSER biogenesis entailed the tight, zipper-like dimerization of the cytoplasmic domains of certain ER-resident proteins. However, the authors found that naturally occurring OSER-inducing proteins can diffuse freely between OSER and ordinary reticular ER, indicating that they are not tightly bound in zipper structures. Weakly dimerizing GFP, and chimeric...