NEMO specifically recognizes K63-linked poly-ubiquitin chains through a new bipartite ubiquitin-binding domain

Area of Science:

• Molecular Biology
• Cellular Biology
• Biochemistry

Background:

• NEMO is a crucial component of the IKK complex, regulating NF-kappaB activation.
• The NOA/UBAN domain of NEMO was previously implicated in poly-ubiquitin chain recognition.
• The C-terminal Zinc Finger (ZF) of NEMO has been identified as a ubiquitin-binding site.

Purpose of the Study:

• To elucidate the specific functions of NEMO's NOA/UBAN and ZF domains in ubiquitin binding.
• To determine the contribution of these domains to K63-linked poly-ubiquitin chain specificity.
• To investigate the structural basis for NEMO's interaction with different ubiquitin chain types.

Main Methods:

• Site-directed mutagenesis to alter NEMO protein domains.
• ZF swapping experiments between NEMO and related proteins.
• Biochemical assays to assess ubiquitin-binding affinity and specificity.

Main Results:

• The C-terminal ZF of NEMO exclusively functions in ubiquitin binding.
• NEMO's NOA and ZF domains cooperate to form a high-affinity, K63-specific ubiquitin-binding domain.
• Similar bipartite domains in Optineurin and ABIN2 are functionally interchangeable with NEMO's domain.
• NEMO's interaction with linear poly-ubiquitin chains relies solely on the NOA domain.

Conclusions:

• The C-terminal half of NEMO primarily functions in binding K63-linked poly-ubiquitin chains through a bipartite domain.
• The NOA domain alone mediates NEMO's interaction with linear poly-ubiquitin chains.
• These findings clarify the distinct roles of NEMO domains in ubiquitin recognition and signaling pathways.