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Papers In Press, published online ahead of print April 14, 2006
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Department of Medicine, Karolinska Institutet, Stockholm 171 76
Corresponding Author: ewa.ehrenborg{at}ki.se
The microsomal triglyceride transfer protein, MTTP is essential for the assembly of very-low density lipoproteins (VLDLs). We have recently observed that a polymorphism in the MTTP promoter (-493G>T), which is in allelic association with an isoleucine-to-theronine substitution at position 128 in the expressed protein, confers an increased risk of coronary heart disease. Two variant proteins comprising amino acids 16-297 of intact MTTP, MTTPN-Ile128 and MTTPN-Thr128, had similar native secondary structure content as judged by Circular Dichroism. However, the thermal stability of the MTTPN-Thr128 was greatly reduced, and was also more extensively cleaved in limited proteolysis experiments compared to MTTPN-Ile128, both of which support a less compact fold. On adding LDL, which includes natively folded apoB, decreased stability of the MTTPN-Thr128-LDL complex was observed compared to that of the MTTPN-Ile128-LDL complex. In a refined model of the N-terminal domain of MTTP, residue 128 is located in a surface-exposed position, in the same region as an identified MTTP binding site in the homologous apoB protein. Thus, the Ile128Thr polymorphism confers a reduced structural stability, leading to decreased binding of MTTP to LDL particles. Since the major MTTP binding target on LDL is apoB, the Ile128Thr polymorphism could target the MTTP-apoB interaction.
Revised on April 10, 2006
Accepted on April 13, 2006
The Ile128Thr polymorphism influences stability and ligand binding properties of the microsomal triglyceride transfer protein
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