X-Rays Provide Detailed View of Hotspots for Calcium-Related Disease

Using intense X-rays, researchers have determined the detailed structure of a critical part of the ryanodine receptor, a protein associated with calcium-related disease.

The study‘s findings, which combine data from Stanford Synchrotron Radiation Lightsource (SSRL; Menlo Park, CA, USA) at the US Department of Energy's SLAC National Accelerator Laboratory and the Canadian Light Source (Saskatoon, Saskatchewan, Canada), pinpoint the locations of more than 50 mutations that cluster in disease "hotspots” along the receptor. "Until now, no one could tell where these disease mutations were located or what they were doing,” said lead investigator Dr. Filip Van Petegem of the University of British Columbia (Vancouver, Canada).

The ryanodine receptor controls the release of calcium ions from a stockroom within skeletal-muscle and heart-muscle cells as needed to perform vital functions. Earlier research at lower resolution indicated that mutations cluster in three regions along the receptor, but without more detailed information it remained unclear precisely how they contributed to disease.

In a study published November 3, 2010, in the journal Nature, Dr. Van Petegem and his group describe the structure of one of these hotspots in extremely fine detail and predict how the mutations might cause the receptor to malfunction and release calcium too soon. The receptor is comprised of more than 20,000 amino acids. Dr. Van Petegem's group studied a string of about 560 amino acids, where they found 57 mutations. In 56 cases, the mutations involved a change in a single amino acid, while the last one involved a deletion of 35 amino acids from the string. "These mutations most likely cause the same disease effects, but a severe mutation leads to stronger symptoms, and doesn't require as big of a stimulus to induce disease,” Dr. Van Petegem said.

In the heart, the receptor is stimulated to open approximately once a second when the body is at rest, transmitting regular pulses of calcium into the rest of the cell. In skeletal muscles, the timing of the pulses is determined by how often the muscles contract. Each time the receptor opens, specific amino acids rearrange themselves to facilitate the calcium release. Mutations can disrupt this process by causing the receptor to open either earlier or more easily than it should.

This premature release of calcium generates extra electrical signals within the cells. In skeletal muscle, this can lead to fatal rises in body temperature under certain anesthetics, or the failure of major muscles. In cardiac muscle, it can trigger an arrhythmia, resulting in sudden cardiac death. While it is difficult to determine the precise number of people with these mutations, it is estimated that as many as one in 10,000 may be at risk for disease.

Future studies at SSRL and other synchrotron facilities will map out other receptor hotspots where these disease mutations cluster and use the detailed information to understand the complex functions of the protein better. "It is very exciting to see the significant impact of our advanced structural biology technologies in helping users address difficult projects,” said SSRL staff scientist Michael Soltis.

Related Links:
Stanford Synchrotron Radiation Light source
Canadian Light Source
University of British Columbia