The linear ubiquitin chain assembly complex (LUBAC) generates heterotypic ubiquitin chains

Area of Science:

• Molecular Biology
• Cellular Biology
• Biochemistry

Background:

• The linear ubiquitin chain assembly complex (LUBAC) is crucial for forming linear/Met1-linked ubiquitin chains.
• HOIL-1L, a LUBAC component, can catalyze oxyester bond formation with ubiquitin and substrates, but this was not observed within LUBAC previously.

Purpose of the Study:

• To visualize human LUBAC structure and its ubiquitin chain assembly mechanism.
• To investigate the role of HOIL-1L catalytic activity in LUBAC-mediated ubiquitin chain formation.

Main Methods:

• 3D reconstruction of human LUBAC using electron microscopy.
• Cross-linking mass spectrometry to analyze protein proximity.
• Analysis of heterotypic ubiquitin chains in mouse embryonic fibroblasts upon TNF stimulation.

Main Results:

• First 3D structure of human LUBAC revealed.
• Demonstrated LUBAC generates heterotypic ubiquitin chains with linear linkages and oxyester-linked branches.
• HOIL-1L catalytic activity is essential for oxyester bond formation in these chains.
• Evidence for a coordinated ubiquitin relay mechanism between HOIP and HOIL-1L.

Conclusions:

• LUBAC assembles heterotypic ubiquitin chains through the combined actions of HOIP and HOIL-1L.
• HOIL-1L's catalytic activity is critical for generating oxyester-linked branches in these chains.
• TNF signaling induces these heterotypic chains, highlighting their biological relevance.