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

Area of Science:

• Cell biology
• Molecular and cell biology
• Biochemistry

Background:

• The Par complex is essential for cell polarization, directing cell membrane organization through atypical protein kinase C (aPKC) activity.
• Upstream regulators Cdc42 and Par-3 bind separately to the Par complex, influencing its function, but their interaction mechanism remains unclear.

Purpose of the Study:

• To elucidate the regulatory mechanism of Par-3 binding to aPKC.
• To understand how Cdc42 and Par-3 binding influences each other's interaction with the Par complex.
• To connect these regulatory events to the overall function of Par complex in cell polarization.

Main Methods:

• Investigated the interaction between Par-3, aPKC, Par-6, and Cdc42.
• Utilized structural biology and biochemical assays to probe protein-protein interactions.
• Analyzed the allosteric regulation of aPKC activity by its binding partners.

Main Results:

• Discovered that Par-3 binding to aPKC is modulated by aPKC autoinhibition.
• Identified a novel interaction between the Par-6 PDZ domain and the aPKC kinase domain, which activates Par-3 binding.
• Demonstrated that Cdc42 and Par-3 exert opposing effects on this interaction, establishing an allosteric relay.

Conclusions:

• The Par complex utilizes an allosteric relay mechanism involving Cdc42, Par-3, Par-6, and aPKC to regulate its activity.
• This mechanism, characterized by negative cooperativity, is fundamental for achieving precise Par complex polarization and cellular patterning.
• The findings provide new insights into the molecular basis of asymmetric cell division and tissue development.