Structural Basis for Mitotic Centrosome Assembly in Flies.

Area of Science:

• Cell Biology
• Structural Biology
• Molecular Biology

Background:

• Centrosomin (Cnn) is crucial for forming scaffolds that recruit proteins to the mitotic centrosome in flies.
• The precise mechanism of Cnn scaffold assembly remains largely unknown.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying Centrosomin (Cnn) scaffold assembly.
• To determine the structural basis for Cnn interactions required for mitotic centrosome formation.

Main Methods:

• In vitro biochemical assays to characterize protein-protein interactions.
• Crystal structure determination of the Leucine Zipper (LZ) and Cnn-motif 2 (CM2) complex.
• In vitro assembly assays with modified LZ domains and Plk1 phosphorylation.
• In vivo studies using mutagenesis to assess the impact on Cnn scaffold assembly.

Main Results:

• Scaffold assembly necessitates conserved Leucine Zipper (LZ) and Cnn-motif 2 (CM2) domains, which form a 2:2 complex.
• The crystal structure reveals LZ and CM2 proteins forming helical dimers that assemble into a tetramer.
• Plk1 phosphorylation in vitro stimulates the formation of micron-scale assemblies between LZ and CM2.
• Mutations disrupting LZ:CM2 tetramer formation impair both in vitro assemblies and in vivo Cnn-scaffold assembly.

Conclusions:

• Cnn molecules possess an intrinsic capacity for large assembly formation dependent on LZ:CM2 interactions.
• These LZ:CM2-mediated assemblies are critical for the proper assembly of the mitotic centrosome.
• This study provides the first atomic-level insights into a key molecular interaction governing mitotic centrosome assembly.