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, crucial for cellular function.
• Disruption of PR signaling is linked to breast cancer development via interactions with co-regulatory proteins (CoRs).
• Detailed molecular mechanisms of how PR isoforms interact with CoRs are not well understood.

Purpose of the Study:

• To investigate the sequential binding mechanism of PR isoforms and CoRs (SRC3, p300) on target DNA.
• To elucidate the structural basis of isoform-specific PR-CoR interactions.
• To understand the role of PR conformation (active vs. inactive) in CoR binding.

Main Methods:

• Utilized structural mass spectrometry to analyze purified full-length PR and intact CoRs (SRC3, p300).
• Examined protein complexes assembled on target DNA.
• Investigated interactions in both antagonist-bound and presumably active conformations.

Main Results:

• Revealed selective binding of CoR NR-boxes by PR.
• Identified unique interaction surfaces between PR and CoRs during complex assembly.
• Observed persistent CoR interactions with antagonist-bound PR, challenging traditional models.

Conclusions:

• Provided a peptide-level structural perspective on the PR transcriptional complex organization.
• Inferred mechanisms governing PR-CoR interactions in both active and inactive states.
• Highlighted the complexity of nuclear receptor regulation beyond classical activation/repression models.