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Impaired cotranslational processing as a mechanism for type I antithrombin deficiency
A C Fitches1, R Appleby, D A Lane
1Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand.
Blood
|December 9, 1998
Summary
A novel mutation in the antithrombin (AT) signal peptide impairs protein processing, leading to hereditary AT deficiency. This discovery highlights the critical role of signal peptide hydrophobicity in protein transport and function.
Area of Science:
- Molecular Biology
- Protein Biochemistry
- Genetics
Background:
- Secretory proteins like antithrombin (AT) require signal peptides for proper cellular export and modification.
- The signal peptide directs nascent proteins to the endoplasmic reticulum (ER) for crucial post-translational events.
Observation:
- A novel mutation (2436T-->C L(-10)P) was identified in the AT signal peptide's hydrophobic domain in a patient with venous thrombosis and AT deficiency.
- Mammalian cell expression revealed that mutations substituting hydrophobic residues at position -10 with P, T, R, or G abolished AT secretion.
Findings:
- Cell-free assays using microsomes demonstrated that these mutations prevent post-translational glycosylation and translocation into the ER.
- The hydrophobic nature of the AT signal peptide, particularly around residue -10, is essential for directing AT to the ER for cotranslational processing.
Implications:
- Impaired cotranslational processing due to signal peptide defects is a newly identified cause of hereditary antithrombin deficiency.
- Understanding signal peptide function is crucial for diagnosing and potentially treating thrombotic disorders linked to AT deficiency.