Molecular requirements for PLK1 activation by T-loop phosphorylation.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Polo-like kinase 1 (PLK1) is a crucial regulator of mitosis.
• PLK1 activation depends on phosphorylation at Thr210, a site typically targeted by Aurora kinases.
• Previous studies presented conflicting evidence regarding the specific Aurora kinase responsible for Thr210 phosphorylation, highlighting the role of Bora, an Aurora A partner.

Purpose of the Study:

• To elucidate the mechanistic basis for the requirement of Bora in PLK1 Thr210 phosphorylation.
• To determine the specific Aurora kinase complex responsible for PLK1 activation.
• To understand the interaction between Bora and PLK1 that facilitates phosphorylation.

Main Methods:

• In vitro kinase assays using purified proteins (Aurora A, Aurora B, Bora, PLK1).
• Site-directed mutagenesis of PLK1 to probe interaction requirements.
• Structural modeling to predict protein interactions.
• Biochemical assays to assess kinase activity and substrate phosphorylation.

Main Results:

• Aurora A complexed with Bora specifically phosphorylated PLK1 Thr210 in vitro.
• Isolated Aurora A, other Aurora A complexes, and Aurora B:INCENP failed to phosphorylate PLK1 Thr210.
• A transient interaction between Bora and PLK1, confirmed by structural modeling and mutation analysis, was essential for Thr210 phosphorylation.
• Mutating Lys208 in PLK1 to arginine abolished Bora dependency, rendering PLK1 a substrate for multiple Aurora kinases.

Conclusions:

• The Aurora A:Bora complex is the primary kinase responsible for PLK1 activation via Thr210 phosphorylation.
• A specific interaction between Bora and PLK1 dictates the kinase specificity for PLK1 activation.
• Understanding this mechanism provides new insights into the regulation of mitotic kinases and cell cycle control.