Allysine

Allysine

Allysine is an amino acid that plays a critical role in the biosynthesis and cross-linking of collagen and elastin, which are essential components of the connective tissue in animals. It is not one of the proteinogenic amino acids that are directly incorporated into proteins during translation. Instead, allysine is formed by the post-translational modification of lysine, another amino acid, within collagen and elastin molecules. This modification is catalyzed by the enzyme lysyl oxidase, which oxidizes the ε-amino group of lysine to form allysine.

Biosynthesis

The biosynthesis of allysine begins with the enzyme lysyl oxidase acting on lysine residues in collagen and elastin precursors. Lysyl oxidase is a copper-dependent enzyme that oxidizes the ε-amino group of lysine to an aldehyde group, resulting in the formation of allysine. This reaction is crucial for the subsequent cross-linking steps that give collagen and elastin their structural integrity and elasticity.

Function

Allysine plays a pivotal role in the formation of cross-links between individual collagen and elastin molecules. After its formation, allysine can react with other amino acid residues, such as lysine or hydroxylysine, to form various types of covalent bonds. These cross-links are essential for the stability and function of the extracellular matrix, contributing to the tensile strength of tissues and the elasticity of blood vessels.

Clinical Significance

Alterations in the activity of lysyl oxidase, and consequently in the formation of allysine, can lead to various connective tissue disorders. For example, a deficiency in lysyl oxidase activity can result in weakened connective tissue, leading to conditions such as Ehlers-Danlos syndrome and Marfan syndrome. On the other hand, excessive cross-linking due to increased lysyl oxidase activity has been associated with fibrotic diseases and the stiffening of arterial walls in atherosclerosis.

See Also

• Collagen
• Elastin
• Lysine
• Lysyl oxidase
• Post-translational modification