Structural proteomics defines a sequential priming mechanism for the progesterone receptor.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The progesterone receptor (PR) is a nuclear receptor with two isoforms, PR-A and PR-B.
• Disruption of PR signaling is linked to breast cancer via interactions with co-regulatory proteins (CoRs).
• Molecular details of isoform-specific PR-CoR interactions are not well understood.

Purpose of the Study:

• To investigate the sequential binding mechanism of PR isoforms and CoRs (SRC3 and p300) on target DNA.
• To elucidate the structural basis of PR-CoR interactions during transcriptional complex assembly.
• To understand the role of PR conformation in CoR binding.

Main Methods:

• Structural mass spectrometry was employed to study purified full-length PR and intact CoRs.
• Analysis focused on complexes formed on target DNA.
• Peptide-level analysis provided insights into protein organization and interactions.

Main Results:

• Selective NR-box binding by PR to CoRs was observed.
• Unique interaction surfaces between PR and CoRs were identified during complex assembly.
• Antagonist-bound PR exhibited persistent CoR interactions, contrary to classical models.

Conclusions:

• The study provides a peptide-level perspective on the PR transcriptional complex organization.
• It offers a structural basis for sequential CoR binding to PR.
• Findings challenge established models of nuclear receptor activation and repression by revealing persistent CoR interactions in inactive conformations.