Golgi function and dysfunction in the first COG4-deficient CDG type II patient.

Area of Science:

• Molecular Cell Biology
• Genetics and Genomics
• Biochemistry

Background:

• The conserved oligomeric Golgi (COG) complex is crucial for glycosylation and intra-Golgi transport.
• Mutations in COG subunits are increasingly linked to congenital disorder of glycosylation type II (CDG-II).
• Understanding COG complex function is vital for deciphering glycosylation disorders.

Purpose of the Study:

• To characterize a novel CDG-II patient with a COG4 mutation and deletion.
• To investigate the impact of COG4 deficiency on COG complex formation, Golgi transport, and glycosylation.
• To conduct a comparative analysis of COG-deficient patients to correlate molecular defects with clinical severity.

Main Methods:

• Genetic analysis to identify mutations (p.R729W missense and submicroscopic deletion in COG4).
• Glycerol gradient centrifugation to assess COG complex formation and subunit stability.
• Comparative analysis of transport, glycosylation, and Golgi ultrastructure in multiple COG-deficient patients.

Main Results:

• A novel COG4 mutation (p.R729W) and deletion led to COG4 downregulation, affecting other COG subunits.
• Full COG complex formation was maintained at a lower level, with evidence of a cytosolic subunit pool.
• COG complex integrity is essential for tethering and membrane fusion; mutation severity correlates with Golgi abnormalities.

Conclusions:

• Intact COG complexes are required for maintaining Golgi dynamics and associated functions.
• The newly identified deficiency is designated CDG-IIj, expanding the spectrum of COG-related disorders.
• This study provides insights into COG complex assembly, function, and its role in human health.