title: Self-aggregation of fibrillar collagens I and II involves lysine side chains.
abstract: 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.
authors.affiliation: Dipartimento di Biochimica, A. Castellani, University of Pavia, via Taramelli 3b, 27100 Pavia, Italy.
authors.forename: Ruggero
authors.initials: R
authors.lastname: Tenni
authors.forename: Myriam
authors.initials: M
authors.lastname: Sonaggere
authors.forename: Manuela
authors.initials: M
authors.lastname: Viola
authors.forename: Barbara
authors.initials: B
authors.lastname: Bartolini
authors.forename: M Enrica
authors.initials: ME
authors.lastname: Tira
authors.forename: Antonio
authors.initials: A
authors.lastname: Rossi
authors.forename: Ester
authors.initials: E
authors.lastname: Orsini
authors.forename: Alessandro
authors.initials: A
authors.lastname: Ruggeri
authors.forename: Vittoria
authors.initials: V
authors.lastname: Ottani
mesh_terms: D000107:Acetylation; D024042:Collagen Type I / Q000737:chemistry* / Q000648:ultrastructure; D024043:Collagen Type II / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008239:Lysine; D046911:Macromolecular Substances / Q000737:chemistry*; D008745:Methylation; D046529:Microscopy, Electron, Transmission; D009391:Nephelometry and Turbidimetry
chemical_list: D024042:Collagen Type I; D024043:Collagen Type II; D046911:Macromolecular Substances; D008239:Lysine