——a major breakthrough in structure determination of drug target based on innovative approach

Using one of the brightest X-ray lasers in the world, a joint research group made up of 28 laboratories led by Dr. H. Eric Xu, a professor from Shanghai Institute of Materia Medica(SIMM), Chinese Academy of Sciences (CAS), have determined the structure of a molecular complex that is responsible for regulating vital physiological function. The new findings provide scientists with a new model for major pharmacological drug targets. The study, Crystal structure of rhodopsin bound to arrestin determined by femtosecond X-ray laser, was published in article in the journal of Nature on 22^nd July, 2015.

The Nobel Prize in chemistry 2012 was shared by Robert J. Lefkowitz and Brian K. Kobilka for their studies on G-protein-coupled receptors（GPCRs）. They uncovered the secret of human information communication system, i.e. how cells sense their environment, and transduce external signal into cell through G protein. However, how GPCRs activate arrestin signaling pathway, a vital issue in the field of GPCR signaling transduction scientists had struggled for many years, is still unanswered.

 “Arrestin and G proteins are playing Yin (negative) and Yang (positive) roles in  regulating GPCR function,” Xu said. Arrestin, as well as other signaling proteins known as G proteins, link up with GPCRs to convey important instructions for many essential physiological functions. Besides the regulation of arrestin in desensitization and internalization of GPCRs, recent research focused on their function on biased GPCR signaling transduction.

The structure determination of membrane protein is still a largely unconquered area. It is more challenging to remap the structural image of large membrane protein complex. For the last decade, a team led by Prof. Xu has worked to unravel the structure of a complex made up of arrestin and rhodopsin, which is a prototypical GPCR responsible for light perception and activating visual function.

The most challenging issue is that the tiny arrestin-GPCR crystals, which Xu’s team had painstakingly produced over years, proved too difficult to study at even the most advanced type of synchrotron, a more conventional X-ray source. Under the cooperation from different disciplines, by utilizing x-ray free-electron laser

(XFEL) which is the most brightest laser in the world, scientists determined the three-dimensional image of Rhodopsin-arrestin complex at an atomic level-a much higher resolution than that is possible gained with older X-ray technology. This structure reveals an overall architecture of the rhodopsin-arrestin assembly, in which arrestin uses distinct interaction mode compared with G protein. This structure provides a basis for understanding GPCR-mediated arrestin-biased signaling and demonstrates the power of X-ray lasers for advancing the frontiers of structural biology.

The discovery solved world-class scientific issue in the field of GPCR signaling transduction, providing a roadmap for developing more selective therapy strategies. “GPCRs are major targets in the development of new therapies and account for almost 40 percent of current drug targets”, said Xu. “In the realm of drug development, a detailed understanding of the structure, interaction and function of each of these groups of proteins is vital to developing effective therapies. The more specific the interaction, the better the drugs tend to work while also lowering the chance of side effects.” Accordingly, drugs only activate the arrestin or G protein signaling pathway, but not both, can have better therapy benefits with fewer undesirable effects than non-selective drugs.

 “This project represented a significant challenge and was accomplished through the work of a multidisciplinary team from many institutions around the globe,” said Xu. “Utilizing the x-ray laser also opens the door for solving future challenging problems.”

 “The Xu group has put together an important story that provides significant insight into our understanding of G-protein-coupled receptor function,” said Jeffrey Benovic, Ph.D., Thomas Eakins Professor at Thomas Jefferson University. “The rhodopsin-arrestin structure helps to explain the process of desensitization and provides a roadmap for obtaining the structure of additional GPCR complexes.”

This work was conducted by Xu’s laboratory at Van Andel Research Institute ,(VARI)in collaboration with VARI’s Karsten Melcher, Ph.D., and collaborators across the globe, including Joint Center for Structural Genomics, Stanford Synchrotron Radiation Light source; LCLS , SLAC National Accelerator Laboratory; VARI-Shanghai Institute of Materia Medica (VARI-SIMM); Arizona State University; University of Southern California; University of California at Los Angeles; DESY’s Center for Free Electron Laser Science; University of Singapore; New York Structural Bio-XFEL Biology Center; The Scripps Research Institute; University of Toronto; Vanderbilt University; NSF Science and Technology Center; University of Wisconsin-Milwaukee; Shanghai Institute of Materia Medica; Paul Scherrer Institute; Trinity College Dublin; University of Chicago; Universität Konstanz; Chinese Academy of Sciences; Centre for Ultrafast Imaging; and University of Toronto.

Besides funds from international sources, this work was also supported by National Basic Research Program of China (973 Program), CAS Strategic Priority Research Program, National Science and Technology Major Project, and Shanghai Commission of Science and Technology, etc.

Link：http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14656.html

Contact person: Dr. H. Eric Xu (eric.xu@simm.ac.cn)

High-resolution 3D structure of Rhodopsin-arrestin complex. Blue, the structure of rhodopsin. Yellow, the structure of arrestin. Rhodopsin is a prototypical GPCR responsible for light perception and visual generation, a process arrestin is involved in.（Image by Xu lab）