The solution structure of functionally active human proliferating cell nuclear antigen determined by small-angle...

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Proliferating cell nuclear antigen (PCNA) functions as a sliding clamp in DNA replication and repair, interacting with DNA polymerases.
• PCNA forms a complex with replication factor C (RF-C) to tether DNA polymerases to DNA.
• PCNA also interacts with cell cycle regulatory proteins, highlighting its multifaceted role.

Purpose of the Study:

• To determine the solution structure of functionally active human PCNA.
• To confirm if the human PCNA protein maintains a ring-like structure in solution, analogous to its yeast counterpart.
• To validate the functional relevance of the observed structure in vivo.

Main Methods:

• Small-angle neutron scattering (SANS) was employed to determine the solution structure of human PCNA.
• Functional assays (RF-C independent and dependent) were performed to assess PCNA activity before and after SANS measurements.
• Model calculations based on the crystal structure of yeast PCNA were used for data comparison.

Main Results:

• Small-angle neutron scattering strongly supports a trimeric ring-like structure for functionally active human PCNA in solution.
• The solution structure data align well with computational models derived from the crystal structure of yeast PCNA.
• Human PCNA demonstrated sustained activity in functional assays, indicating the trimeric ring is the in vivo functional form.

Conclusions:

• The trimeric ring structure of human PCNA is maintained in solution and is consistent with its known functions.
• The findings support the conservation of PCNA structure and function across species (yeast and human).
• The study validates the trimeric ring as the biologically relevant, in vivo functional conformation of human PCNA.