MZT Proteins Form Multi-Faceted Structural Modules in the γ-Tubulin Ring Complex

Area of Science:

• Cell Biology
• Structural Biology
• Biochemistry

Background:

• Microtubule organization is essential for cellular processes.
• The γ-tubulin ring complex (γ-TuRC) is the primary nucleation factor for microtubules.
• The roles of MZT1 and MZT2 in γ-TuRC structure and regulation are not well understood.

Purpose of the Study:

• To elucidate the structural contribution of MZT1 and MZT2 to the human γ-TuRC holocomplex.
• To understand how these microproteins influence the nucleation factor's assembly and function.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine structures of MZT1 and MZT2 within native human γ-TuRC.
• X-ray crystallography of recombinant MZT1/GCP6-NHD subcomplex.
• Identification and structural characterization of MZT/GCP-NHD interactions.

Main Results:

• MZT1 forms two subcomplexes with GCP-NHDs (GCP3 or GCP6) within the γ-TuRC lumenal bridge.
• The X-ray structure of recombinant MZT1/GCP6-NHD mirrors its native conformation.
• MZT2 and GCP2-NHD, along with a CM1-containing peptide, form an additional module on the γ-TuRC outer face.

Conclusions:

• MZT1 and MZT2 act as modular components that expand the structural and regulatory capacity of the γ-TuRC.
• These microproteins establish multi-faceted, structurally mimetic interfaces within the holocomplex.
• The findings provide critical insights into the regulation of microtubule nucleation by the γ-TuRC.