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Structure of the human CTF18-RFC clamp loader bound to PCNA
Giuseppina R Briola1, Muhammad Tehseen1, Amani Al-Amodi1
1Bioscience Program, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia.
Biorxiv : the Preprint Server for Biology
|August 8, 2025
Summary
The human CTF18-RFC complex, a key DNA clamp loader, has been structurally characterized. Its unique features facilitate the loading of PCNA, crucial for DNA replication and Pol ε-mediated synthesis.
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- Sliding clamps, such as PCNA (proliferating cell nuclear antigen), are essential for DNA replication fidelity.
- Clamp loaders are required to load sliding clamps onto DNA, a process vital for processivity.
- CTF18-RFC is an alternative human clamp loader that interacts with DNA polymerase epsilon (Pol ε).
Purpose of the Study:
- To structurally characterize the human CTF18-RFC complex and its interaction with PCNA.
- To elucidate the mechanism by which CTF18-RFC loads PCNA onto DNA.
- To understand the role of CTF18-RFC in stimulating leading strand DNA synthesis by Pol ε.
Main Methods:
- Cryo-electron microscopy (cryo-EM) was used to determine the structure of the CTF18-RFC-PCNA complex.
- Biochemical assays were employed to assess the function of CTF18-RFC in clamp loading and DNA synthesis.
Main Results:
- A 2.9 Å cryo-EM structure revealed the CTF18-RFC complex bound to PCNA in an auto-inhibited state.
- The Ctf8 and Dcc1 subunits are flexibly tethered to the RFC module, interacting with Pol ε.
- A novel β-hairpin in the Ctf18 subunit's N-terminus is crucial for CTF18-RFC-PCNA complex stability and function.
Conclusions:
- The human CTF18-RFC complex possesses unique structural features that distinguish it from canonical clamp loaders.
- The identified structural characteristics provide insights into the mechanism of PCNA loading by CTF18-RFC.
- CTF18-RFC plays a significant role in stimulating leading strand synthesis by Pol ε, highlighting its importance in DNA replication.
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