Self-aggregation of fibrillar collagens I and II involves lysine side chains
- 作者：Ruggero Tenni ; Myriam Sonaggere ; Manuela Viola ; Barbara Bartolini ; M. Enrica Tira ; Antonio Rossi ; Ester Orsini ; Alessandro Ruggeri and Vittoria Ottani
- 关键词：Collagen ; Fibril formation ; Fibril morphology ; Protein modification ; Lysine ; Aggregates stability
- 刊名：Micron
- 出版年：2006
- 期刊代码：37_09684328
- 类别：ph
- 出版时间：October 2006
- 卷：37
- 期：7
- 页码：640-647
- 文件大小：550 K
摘要
Several properties of fibrillar collagens depend on abundance and position of ionic amino acids. We recently demonstrated that N-methylation and N-acetylation of Lys/Hyl amino group did not significantly alter the thermal stability of the triple helical conformation and that the binding of modified collagens I and II to decorin is lost only on N-acetylation. The positive charge at physiological pH of Lys/Hyl side chains is preserved only by N-methylation. We report here the new aspect of the influence of the same modifications on collagen self-aggregation in neutral conditions. Three collagen preparations are very differently affected by N-methylation: acid-soluble type I collagen maintains the ability to form banded fibrils with 67-nm periodicity, whereas almost no structured aggregates were detected for pepsin-soluble type I collagen; pepsin-soluble type II collagen forms a very different supramolecular species, known as segment long spacing (SLS). N-acetylation blocks the formation of banded fibrils in neutral conditions (as did all other chemical modifications reported in the literature), demonstrating that the positive charge of Lys/Hyl amino groups is essential for self-aggregation. Kinetic measurements by turbidimetry showed a sizeable increase of absorbance only for the two N-methylated samples forming specific supramolecular aggregates; however, the derivatization affects aggregation kinetics by increasing lag time and decreasing maximum slope of absorbance variation, and lowers aggregation competency. We discuss that the effects of N-methylation on self-aggregation are caused by fewer or weaker salt bridges and by decrease of hydrogen bonding potential and conclude that protonated Lys side chains are involved in the fibril formation process.