Proteins Park Free in this Helix
Posted on by Dr. Francis Collins
I simply couldn’t resist sharing this image with you, even though the NIH didn’t fund the research. What you see in this picture is a structure called the endoplasmic reticulum (ER)—a protein-producing factory that is present in every single cell in your body. The little nubs on the surface of this membranous structure are ribosomes—they produce the proteins that are then modified in the ER.
The ER was discovered more than 60 years ago but its structure is so complicated that we’ve never had a detailed three-dimensional view. Textbook images have typically depicted the ER like a pile of pancakes. But a team based at Harvard and the University of Connecticut Health Center developed a new technique to stain this microscopic structure. Then they used a new scanning electron microscopy method to show how each level of membrane is connected by a helical ramp—like the ramps in a multi-level parking lot. The advantage of this geometry is that you can stack a lot of membranes in a small area—that’s vital because the cell doesn’t have a lot of unused real estate. Another feature is that when the cells need to produce a lot of proteins this structure can add on additional levels of membrane—effectively increasing the manufacturing capacity of this organ. Too bad the NIH parking decks can’t also expand and contract as needed!
 Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs. Terasaki M, Shemesh T, Kasthuri N, Klemm RW, Schalek R, Hayworth KJ, Hand AR, Yankova M, Huber G, Lichtman JW, Rapoport TA, Kozlov MM. Cell. 2013 Jul 18;154(2):285-96.