9IIN

Structure of CTF18-PCNA with ATP and Mg2+

Summary for 9IIN

• Entry DOI: 10.2210/pdb9iin/pdb
• EMDB information: 60598
• Descriptor: Chromosome transmission fidelity protein 18 homolog, Replication factor C subunit 2, Replication factor C subunit 5, ... (9 entities in total)
• Functional Keywords: ctf18-rfc, human clamp loader; pcna, sliding clamp; complex, atp, dna binding protein
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 8
• Total formula weight: 361178.13

Authors

Briola, G.R.,Tehseen, M.,Al-Amodi, A.,Nguyen, P.Q.,Savva, C.G.,Hamdan, S.M.,De Biasio, A. (deposition date: 2024-06-20, release date: 2025-06-25, Last modification date: 2025-08-27)

Primary citation

Briola, G.R.,Tehseen, M.,Al-Amodi, A.,Young, G.,Danazumi, A.U.,Nguyen, P.Q.,Savva, C.G.,Hedglin, M.,Hamdan, S.M.,Biasio, A.
Structure of the human CTF18-RFC clamp loader bound to PCNA.
Biorxiv, 2025

PubMed Abstract: Sliding clamps like PCNA are crucial processivity factors for replicative polymerases, requiring specific clamp loaders for loading onto DNA. The human alternative clamp loader CTF18-RFC interacts with the leading strand polymerase Pol ε and loads PCNA onto primer/template DNA using its RFC pentameric module. Here, we provide a structural characterization of the human CTF18-RFC complex and its interaction with PCNA. Our cryo-EM data support that the Ctf8 and Dcc1 subunits of CTF18-RFC, which form the regulatory module interacting with Pol ε, are flexibly tethered to the RFC module. A 2.9 Å cryo-EM structure shows the RFC module bound to PCNA in an auto-inhibited conformation similar to the canonical RFC loader, marking the initial step of the clamp-loading reaction. The unique RFC1 (Ctf18) large subunit of CTF18-RFC, which based on the cryo-EM map shows high relative flexibility, is anchored to PCNA through an atypical low-affinity PIP box in the AAA+ domain and engages the RFC5 subunit using a novel β-hairpin at the disordered N-terminus. We show that deletion of this β-hairpin impairs the CTF18-RFC-PCNA complex stability, slows down clamp loading, and decreases the rate of primer synthesis by Pol ε. Our research identifies distinctive structural characteristics of the human CTF18-RFC complex, providing insights into its role in PCNA loading and the stimulation of leading strand synthesis by Pol ε.

PubMed: 40777363
DOI: 10.1101/2024.05.08.593111

Experimental method

ELECTRON MICROSCOPY (3.2 Å)