INJURY-INDUCED ENZYMATIC METHYLATION OF AGING COLLAGEN IN THE EXTRACELLULAR-MATRIX OF BLOOD-VESSELS

As a result of blood vessel injury, protein D-aspartyl/L-isoaspartyl c arboxyl methyltransferase (PIMT), a normally intracellular enzyme, bec omes trapped within the meshwork of the vascular extracellular matrix where it can methylate substrate proteins. In this investigation we ex amined the distribution of such altered aspartyl-containing substrate proteins in the vascular wall. Nearly 90% of all the altered aspartyl residues were inaccessible to intracellular PIMT. Proteins of the extr acellular matrix were found to be the major repository of altered aspa rtyl-containing polypeptides in the blood vessel wall, accounting for similar to 70% of the total amount. Proteolytic cleavage of extracellu lar matrix proteins with cyanogen bromide (CNBr) revealed that collage ns account for most of the altered aspartyl-containing proteins of the ECM. As a consequence of blood vessel injury, both type I and type II I collagen along with other proteins were found to become methylated b y injury-released PIMT. It is estimated that 1 cm of vein contains on the order of 5x10(14) altered aspartyl residues involving between 1% a nd 5% of the total extracellular protein.