Lysyl oxidase: new looks on LOX.

The extracellular matrix proteins collagen and elastin determine, to a large extent, the biomechanical properties of the vessel wall. Both molecules are secreted as monomers, but are posttranslationally modified in the extracellular space in order to generate stable polymers. A critical feature of collagen and elastin fibers is the degree of cross-linking. The first step in cross-linking is the oxidative deamination of the -amino group of certain peptidyl (hydroxy)lysyl residues, resulting in the aldehyde (hydroxy)allysine. In collagen, (hydroxy)allysine is restricted to the Cand N-telopeptide. The aldehyde reacts with a lysyl (Lys) or hydroxylysyl (Hyl) residue in the triple helix, resulting in a variety of cross-links.1 In elastin, the oxidative deamination of Lys (Hyl is absent in elastin) is less restrictive, resulting in modification of most of the Lys residues. Well known elastin cross-links are lysinonorleucine and the pyridiniums desmosine and isodesmosine.1 The cross-links in collagen are responsible for the stiffness of collagen fibers,2 whereas the cross-links in elastin are important for the rubber-like properties of elastin fibers.3