A PDZ-kinase allosteric relay mediates Par complex regulator exchange.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The Par complex regulates cell polarity in animal cells through atypical Protein Kinase C (aPKC).
• Cdc42 and Par-3 are upstream regulators that bind separately to the Par complex, influencing its activity.
• The distinct binding sites of Cdc42 and Par-3 raise questions about their cross-regulation.

Purpose of the Study:

• To investigate the regulatory interplay between Cdc42, Par-3, and the Par complex.
• To elucidate the mechanism by which Par-3 binding to aPKC is modulated.
• To understand how these interactions contribute to Par complex-mediated cell polarization.

Main Methods:

• Biochemical assays to study protein interactions.
• Analysis of autoinhibition mechanisms within aPKC.
• Investigating the role of the Par-6 PDZ domain in regulating aPKC activity.

Main Results:

• Par-3 binding to aPKC is regulated by aPKC autoinhibition.
• The Par-6 PDZ domain activates aPKC binding to Par-3 through a novel interaction with the aPKC kinase domain.
• Cdc42 and Par-3 exert opposing effects on the Par-6 PDZ-aPKC kinase interaction, establishing an allosteric relay.

Conclusions:

• An allosteric relay mechanism connects Cdc42 and Par-3 binding sites within the Par complex.
• This relay, involving differential effects on the Par-6 PDZ-aPKC kinase interaction, underlies the negative cooperativity essential for Par complex polarization and activity.