Using the same technology available in smartphone cameras, Columbia scientists are capturing images of individual molecules at a level of detail never before possible—including images of a molecule implicated in heart failure, age-related muscle weakness, and muscular dystrophy.
The new images of the ryanodine receptor, a membrane protein that functions as a channel for the passage of calcium ions in muscle cells, have led to the determination of its 3-D structure in unprecedented detail. The newly discovered structure will help researchers understand how the molecule works, why it fails in heart and skeletal muscle disease, and how to design drugs to improve the function of faulty receptors.
The findings emerged from a collaboration among the laboratories of Andrew Marks, MD, an expert in the physiology of ryanodine receptors; Joachim Frank, PhD, an expert in electron microscopy; and Wayne Hendrickson, PhD, an eminent X-ray crystallographer.
Biological molecules are tiny, with even the largest molecules only 1/10,000th as large as the width of a human hair.
The highest resolution images of such molecules have traditionally been captured using X-ray diffraction from precisely arranged crystals of the molecule of interest. Unfortunately, making crystals of many of the biomolecules of most interest to biologists and pharmaceutical companies is challenging and, for some, nearly impossible.
A wider variety of biomolecules can be imaged with electron microscopy, which does not require crystals. But until the advent of new cameras, the resolution of such images was often too low to obtain the exquisite details required by drug designers.
One of the first of the new cameras was deployed in 2012 in the lab of Dr. Frank, professor of biochemistry & molecular biophysics, who developed the approach of determining the structure of molecules from many single images.
Like its smartphone counterpart, the camera uses active pixel sensor technology, which provides superior resolution, higher contrast, and fewer image artifacts than the charged couple device-based cameras used previously.
When the ryanodine receptor channel works correctly, the molecule regulates contractions in heart and skeletal muscle by controlling the passage of calcium ions through its central pore. When the channel malfunctions, calcium leaks through the pore, exacerbating heart failure or causing muscle weakness.
Previous attempts by Dr. Frank to uncover the ryanodine receptor’s shape in the early 90s revealed the general outlines of the molecule, including the pore. But details vital to understanding how the molecule works and how defects in it cause disease remained obscure.
The new camera model reveals these details, as well as some that had not been anticipated. Biologists can now see where mutations in the ryanodine receptor channel occur, understand how those mutations affect the functioning of the channel, and model how the receptor channel opens and closes. “Having the structure in hand will completely change the field of ryanodine receptor channel research,” says Dr. Marks. “It will give us new insights into how the drugs work and how to make them work better.”
This is a summary of research published in Nature, Jan. 1, 2015.