Isolation and characterization of new cross-linking amino acid "allodesmosine" from hydrolysate of elastin

Unique molecular networks: Formation and role of elastin cross-links

Elastic fibers are essential assemblies of vertebrates and confer elasticity and resilience to various organs including blood vessels, lungs, skin, and ligaments. Mature fibers, which comprise a dense and insoluble elastin core and a microfibrillar mantle, are extremely resistant toward intrinsic and extrinsic influences and maintain elastic function over the human lifespan in healthy conditions. The oxidative deamination of peptidyl lysine to peptidyl allysine in elastin's precursor tropoelastin is a crucial posttranslational step in their formation. The modification is catalyzed by members of the family of lysyl oxidases and the starting point for subsequent manifold condensation reactions that eventually lead to the highly cross-linked elastomer. This review summarizes the current understanding of the formation of cross-links within and between the monomer molecules, the molecular sites, and cross-link types involved and the pathological consequences of abnormalities in the cross-linking process.

Advances in biomimetic regeneration of elastic matrix structures

Elastin is a vital component of the extracellular matrix, providing soft connective tissues with the property of elastic recoil following deformation and regulating the cellular response via biomechanical transduction to maintain tissue homeostasis. The limited ability of most adult cells to synthesize elastin precursors and assemble them into mature crosslinked structures has hindered the development of functional tissue-engineered constructs that exhibit the structure and biomechanics of normal native elastic tissues in the body. In diseased tissues, the chronic overexpression of proteolytic enzymes can cause significant matrix degradation, to further limit the accumulation and quality (e.g., fiber formation) of newly deposited elastic matrix. This review provides an overview of the role and importance of elastin and elastic matrix in soft tissues, the challenges to elastic matrix generation in vitro and to regenerative elastic matrix repair in vivo, current biomolecular strategies to enhance elastin deposition and matrix assembly, and the need to concurrently inhibit proteolytic matrix disruption for improving the quantity and quality of elastogenesis. The review further presents biomaterial-based options using scaffolds and nanocarriers for spatio-temporal control over the presentation and release of these biomolecules, to enable biomimetic assembly of clinically relevant native elastic matrix-like superstructures. Finally, this review provides an overview of recent advances and prospects for the application of these strategies to regenerating tissue-type specific elastic matrix structures and superstructures.

Catalytic properties and structural components of lysyl oxidase

Key aspects of the biosynthesis and catalytic specificity of lysyl oxidase (LO) have been explored. Oxidation of peptidyl lysine in synthetic oligopeptides is markedly sensitive to the presence of vicinal dicarboxylic ami/no acid residues. Optimal activity is obtained with the -Glu-Lys- sequence within a polyglycine 11-mer, whereas the -Lys-Glu- sequence is much less efficiently oxidized. The -Asp-Glu-Lys- sequence is a very poor substrate, although this sequence is oxidized in type I collagen fibrils. These results are considered in the light of a model requiring collagen to be assembled as fibrils prior to oxidation by LO. An in vitro system for the expression of catalytically active LO has been devised. Deletion or inclusion of the cDNA coding for the propeptide region in the expressed construct results in apparently identical, catalytically active enzyme products, indicating the lack of essentiality of this region for active enzyme production. These effects are considered with respect to the conservation of the amino acid sequence of LO produced by different species.

Mechanism of formation of elastin crosslinks

We examined the formation of quaternary pyridinium crosslinks of elastin formed by condensation of lysine and allysine residues using the model compounds propanal (allysine) and n-butylamine (lysine) under quasi-physiological conditions. The resulting pyridinium compounds were characterized and the structure compared with the known pyridinium crosslinks. Three pyridinium compounds were identified and the structures were identical with the skeleton of the crosslinking amino acids, desmosine (DES), isodesmosine (IDE), and pentasine. We concluded that a non-enzymatic pathway is available for the spontaneous generation of pyridinium crosslinks. To elucidate the intermediates and the mechanism of the formation of DES and IDE, we synthesized model intermediates from propanal and n-butylamine, and they were allowed to react in three kinds of solvents. Then, the products were analyzed by an ion-pair reverse-phase HPLC. The results of this model system indicated that DES and IDE can be formed by condensation of dehydromerodesmosine with dehydrolysinonorleucine and by condensation of allysine with dehydrolysinonorleucine, respectively. We also describe the mechanism of DES and IDE crosslinking.

Cyclopentenosine, major trifunctional crosslinking amino acid isolated from acid hydrolysate of elastin

A trifunctional crosslinking amino acid named cyclopentenosine (CP) was isolated from the hydrolysate of bovine nuchal ligament elastin. CP and its derivatives were identified by spectroscopic methods. CP was found to consist of a 2-cyclopenten-1-one structure and its imine-enamine tautomers with enantiomers in H(2)O. A model reaction for the formation of the CP crosslink using model compounds for allysine (propanal) and lysine (n-butylamine) demonstrated that CP is composed of 2-cyclopenten-1-one and alpha, beta, gamma, delta-unsaturated aldehyde derived from three allysine residues. An ion-paired high-performance liquid chromatographic method for the determination of CP was developed. Among various bovine tissues the nuchal ligament had the highest concentration of CP. The age-related changes in the concentration of CP were examined in the aorta from rat (short-lived species) and bovine (long-lived species). The CP content was very low in the newborn rat but increased markedly with growth. After maturity, the CP content remained nearly the same or slightly decreased. In bovine aorta, the CP content scarcely changed from 7 months to 16 years.

Alteration of cross-linking amino acids of elastin in human aorta in association with dissecting aneurysm: analysis using high performance liquid chromatography

Elastic fiber is one of the major component of the extracellular matrix, which provides the resilience to many tissues. Elasticity is an important property of human aorta, and this elastic property decreases in various pathological conditions such as dissecting aneurysm (DA). Since the cross-linking structures in elastin are responsible for this elasticity, we studied the alteration of various cross-linking amino acids in human aorta associated with DA by a new method using high-performance liquid chromatography (HPLC). Materials were obtained from non-atherosclerotic areas of thoracic aorta of 27 autopsy cases which had no particular aortic disease and 19 cases of DA at replacement operation. After acid hydrolysis, SEP-PAK silica-gel column and Fe3+/activated charcoal column pretreatment were carried out for analysis of desmosine (DES), isodesmosine (ISDES), neodesmosine (NEO), oxodesmosine (OXO) and isooxodesmosine (ISOXO), and for analysis of aldosine (ALD), respectively. These prepared samples were applied to the reversed-phase HPLC column. We also analyzed pyridinoline (PYR), a major cross-linking amino acid of collagen as an index of fibrosis. All crosslinks of elastin were decreased in DA as compared to the age-matched control. The decrease of ISOXO was marked. The increase of PYR and PYR/(DES+ISDES) were not statistically significant. It is suggested oxidative degradation on elastin crosslinks occur in DA, and the ratio of collagen to elastin didn't contribute to the pathogenesis of DA.

Age-related alteration of cross-linking amino acids of elastin in human aorta

It is well known that the elastic property of human aorta decreases gradually with age. Since the cross-linking structures are responsible for this elasticity, age-related changes of cross-linking amino acids in human aorta were studied using a high-performance liquid chromatography (HPLC). Non-atherosclerotic areas of thoracic aorta of 27 autopsy cases which had no particular aortic disease were obtained. After acid hydrolysis, SEP-PAK silica-gel column and Fe3+/activated charcoal column pretreatment were carried out for analysis of desmosine (DES), isodesmosine (ISDES), neodesmosine (NEO), oxodesmosine (OXO) and isooxodesomosine (ISOXO), and for analysis of aldosine (ALD), respectively. These prepared samples were applied to the reversed-phase HPLC column. We also analyzed pyridinoline (PYR), a major cross-linking amino acid of collagen as an index of fibrosis. All cross-linking amino acids of elastin rapidly increased in infancy and then gradually decreased with age. In the middle- and old-age, the amount of OXO showed marked variety. PYR was little detected at 0-year-old, and then gradually increased with age. The crosslinks of elastin were rapidly formed in childhood and then decreased with age. These findings suggest that the relative increase of NEO, OXO or ISOXO to DES and ISDES is associated with age-related weakening and/or damage of elastin, and that the gradual shift from elastin- to collagen-dominant state is a possible cause of the loss of elasticity and the gain of stiffness in the aging aorta.

Post-translational chemical modifications of proteins--III. Current developments in analytical procedures of identification and quantitation of post-translational chemically modified amino acid(s) and its derivatives

1. The Chemical modifications of amino acids and their derivatives are mainly due to different post-translational enzymatic reactions. 2. The enzymatic reactions resulting in amino acids such as acetylation-, formylation, methylation-phosphorylation-, sulfation-, hydroxylation, ADP ribosylation-, carboxylation-, amidation-, adenylylation-, glycosylation-, ubiquitination-, prenylation and acylation are listed and analytical methods are reported and extensively reviewed. 3. The post-translationally modified cross-linking molecules after maturations such as desmosines, allo-desmosine, hydroxy-, lysylpyridinoline, 3-hydroxypyridinium derivatives, cyclopentenosine recently found in matured elastin, and in collagen, and pulcherosine a novel tyrosine-derived found in fertilization envelope of Sea Urchin embryo, di-tyrosine in resilin, gamma-glutamyl-lysine isopeptide cross-linking molecule etc. are listed and both physico-chemical and analytical methods are extensively reviewed and discussed. 4. Other consequences of post-translational modifications encountered in the analytical procedure such as N-terminal step-wise Edman degradation of glycosylated site(s), phosphorylated-site(s) and or sulfated-site(s) were also reported by us.