The present study unravels key differences between prokaryotic Ago (pAgo) and eukaryotic Ago (eAgo) enzymes in the cleavage reaction and may provide important clues on their evolutionary past.
For Ago in eukaryotes, these two symmetric positively-charged residues play the identical role that is critical for cleavage. Hence, it was long speculated that the two analogous resides in prokaryotic Ago perform the same critical role in cleavage function. Surprisingly, this study showed that in pAgo, only one (Arginine 545) of the two residues is involved in cleavage function. When the other one (Arginine 486) was substituted with other amino acids, the enzyme was still able to maintain its cleavage activity. Based on these results, the study further suggested that R486 may play other roles such as assisting the insertion of the glutamate finger. The discovery of such striking differences in the roles of these symmetric resides between eAgos and pAgos provides novel insights on how the cleavage functions evolve during the evolution journey from prokaryote to eukaryote.
To achieve these results, computational methods combining Quantum Mechanics, Molecular Mechanics, and Molecular Dynamics (QM/MM) were applied to elucidate the cleavage reaction mechanism and identify functional roles of the amino acid residues. This research was made possible by large-scale high-performance computing resources, which were computed equivalent to 10,000 CPU cores for 25 weeks on the Shaheen II Supercomputer at KAUST in collaboration with Prof. Xin GAO’s group.
“This research was made possible due to current day computing capabilities and the precision that QM/MM modelling allows for,” said Prof. HUANG Xuhui. “Comparing which amino acid residues play a key part in the target DNA/RNA cleavage step in pAgo and eAgo sheds light on how Ago protein evolves from prokaryotes to eukaryotes to cleave DNA/RNA. This information may be useful in ultimately modifying the Ago protein for use as an enhanced gene editing tool in the future,” Prof. Huang explained.
Jinping Lei, Gang Sheng, Peter Pak-Hang Cheung, Shenglong Wang, Yu Li, Xin Gao, Yingkai Zhang, Yanli Wang, Xuhui Huang. Two symmetric arginine residues play distinct roles in Thermus thermophilus Argonaute DNA guide strand-mediated DNA target cleavage. Proceedings of the National Academy of Sciences, 2019; 116 (3): 845 DOI: 10.1073/pnas.1817041116