IDENTIFICATION OF AN ELASTIN CROSS-LINKING DOMAIN THAT JOINS 3 PEPTIDE CHAINS - POSSIBLE ROLE IN NUCLEATED ASSEMBLY

The alignment of elastin molecules in the mature elastic fiber was inv estigated by purifying and sequencing crosslink-containing peptides ge nerated by proteolytic digestion of incompletely cross-linked insolubl e elastin. Peptides of interest were purified by reverse phase and siz e exclusion high performance liquid chromatography and characterized b y amino acid analysis and protein sequencing. One peptide, consisting of the cross-linking domain encoded by exon 10, contained a modified l ysine residue that had not condensed to form a polyfunctional cross li nk. Although this domain contains the characteristic paired lysine res idues found in other cross-linking domains of elastin, protein sequenc e analysis indicated that the first but not the second lysine had been oxidized by lysyl oxidase. This finding suggests that lysine residues in an individual cross-linking domain may not have equal susceptibili ty to oxidation by lysyl oxidase. In a second peptide, we found that a major cross-linking site in elastin is formed through the association of sequences encoded by exons 10, 19, and 25 and that the three chain s are joined together by one desmosine and two lysinonor-leucine cross -links. Past structural studies and computer modeling predict that dom ains 19 and 25 are linked by a desmosine cross-link, while domain 10 b ridges domains 19 and 25 through lysinonorleucine cross-links. These f indings, together with the high degree of sequence conservation for th ese three domains, suggest an important function for these regions of the molecule, possibly nucleating the aggregation and polymerization o f tropoelastin monomers in the developing elastic fiber.