Solution Structure of Proline- and Glycine-Arginine Dipeptide Repeats Studied by Small-Angle X-Ray Scattering and Molecular Structural Simulation

Bing-Jun Lian^1,3*, Kai-Tai Lin^1,3, Yu-Jen Chang², Orion Shih¹, Kuei-Fen Liao¹, Yi-Qi Yeh¹, Yun-Ru Chen², U-Ser Jeng^1,3

¹National Synchrotron Radiation Research Center, Hsinchu, Taiwan
²Genomics Research Center, Academia Sinica, Taipei, Taiwan
³Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Bing-Jun Lian, email:robby.lien0507@gmail.com

Segments of abnormal dipeptide repeats are often found in the gene chromosome 9 open reading frame 72 (C9ORF72) in the patients of familial frontotemporal dementia (a progressive disorder of the brain) and amyotrophic lateral sclerosis (muscles decreasing in size, resulting in difficulty in speaking, swallowing, and eventually breathing), as a signature of the diseases. Such dipeptide repeating of 10 – 1000 times can be found in the brain or spinal cord of the patients, including poly Glycine-Arginine (GR)n, poly Glycine-Alanine (GA)n, poly Glycine-Proline (GP)n, poly Proline-Arginine (PR)n, and poly Proline-Alanine (PA)n. Current research shows that both GR and PR are cytotoxic, especially PR is more cytotoxic than GR in Drosophila-eye experiment. Up to date, there are no crystal structures available for these intrinsic disorder dipeptide repeats. To reveal structural insights of the repeating length of the dipeptide repeats (DPRs) on the development of the disease symptoms, we have synthesized (PR)₃₀ and compared to (GR)₃₀ by integrative analysis of small-angle X-ray scattering (SAXS) and molecular structural simulation. With the combined analysis protocol of Rosetta-SAXS, an energy minimized structure that can describe the SAXS data is obtained. The result shows that, different from the helical structure of (GR)₃₀, (PR)₃₀ form a long-chain backbone conformation with charged sidechains extending out in solution.In the future, we’ll try to resolve the structure of PR/GR-ssDNA complex and improve the quality of separation by Field-flow separation system.

Keywords: Dipeptide repeats, Proline-Arginine, Small-Angle X-Ray Scattering, Molecular structural simulation