OGT (O-GlcNAc Transferase) Selectively Modifies Multiple Residues Unique to Lamin A

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• The LMNA gene encodes lamins A and C, essential for nuclear structure and genome integrity.
• Mutations in LMNA cause over 12 distinct diseases, termed laminopathies.
• Lamins A and C, though sharing initial sequences, form distinct filaments with unique functions.

Purpose of the Study:

• To investigate the post-translational modification of lamins A and C.
• To identify specific sites and enzymes involved in lamin modification.
• To explore the functional implications of these modifications, particularly in relation to laminopathies.

Main Methods:

• In vitro assays using purified O-GlcNAc transferase (OGT) enzyme.
• Mass spectrometry to identify O-GlcNAc sites on lamin A.
• Analysis of recombinant lamin A tails with specific deletions (Δ50, Δ35) and mutations (S612A/T643A).

Main Results:

• Lamin A, but not Lamin C or Lamin B1, undergoes O-GlcNAc modification in vitro and in vivo.
• Eleven O-GlcNAc sites were identified in a region unique to lamin A, with up to seven sugars per peptide.
• Deletions associated with progeria (Δ50) abolished modification, while Δ35 significantly reduced it, suggesting key roles for specific residues.

Conclusions:

• Lamin A is selectively modified by O-GlcNAc, indicating a novel regulatory pathway.
• Residues deleted in progeria are critical for OGT recognition and/or modification of lamin A.
• This O-GlcNAc modification of lamin A may have profound functional implications and warrants further in vivo investigation.