Structural Basis for Regulation of ESCRT-III Complexes by Lgd

Area of Science:

• Cell Biology
• Structural Biology
• Molecular Mechanisms

Background:

• The ESCRT-III complex drives membrane remodeling, essential for processes like viral budding and cytokinesis.
• Shrub (CHMP4B) is a core component of ESCRT-III, whose polymerization drives membrane deformation.
• Shrub activity is modulated by interactions with regulatory proteins, including Lgd (CC2D1A/B).

Purpose of the Study:

• To elucidate the structural basis of the Lgd-Shrub interaction.
• To understand the mechanism by which Lgd regulates Shrub polymerization and ESCRT-III activity.

Main Methods:

• X-ray crystallography to determine the structure of the Lgd DM14 domain bound to Shrub.
• Biochemical assays to assess the binding affinity and functional impact of mutations.
• In vivo studies in Drosophila to validate the functional significance of the interaction.

Main Results:

• The isolated third DM14 repeat of Lgd, along with its C2 domain, is sufficient for in vivo function.
• The Lgd DM14 domain, as a helical hairpin, binds to a negatively charged surface on Shrub.
• This binding site on Shrub is also utilized for homopolymerization, indicating a direct competition.
• Mutations at the Lgd-Shrub interface impair Lgd function in vivo.

Conclusions:

• Lgd regulates ESCRT-III by sterically blocking the Shrub self-assembly interface.
• The structural data provide a mechanistic explanation for Lgd-mediated regulation of ESCRT-III.
• This interaction is crucial for controlling membrane budding and fission events mediated by ESCRT-III.