V. Guantieri

Interactions of Human and Bovine Elastins with Lipids: Their Proteolysis by Elastase

The elastase-catalyzed hydrolysis of elastin extracted from young and old human aortas was compared with that of elastin from a bovine source. The course of the elastolysis was followed in the presence of sodium taurocholate and some unsaturated fatty acids. The results obtained suggest interesting correlations between the effects of aging on elastin, interaction of elastin with lipids and its susceptibility to proteolysis by elastase.

Spectroscopic studies on elastin-like synthetic polypeptides

Spectroscopic studies on synthetic polypeptides containing the unit-X-G-G (X=V or L) are reported. The sequences, constituting either fragments or model of elastin, were shown to adopt type II beta-turns together with an ensemble of unordered conformations. Furthermore, it was found that the stability of the beta-turns was depending on the nature of the X residue, on the hydration of the chain and, in the case of the sequence G-V-G-G-L, was decreasing by increasing the length of the chain.

Solid-state studies on synthetic fragments and analogues of elastin

A series of synthetic fragments and analogues of elastin have been investigated, in the solid state, by means of differential scanning calorimetry and thermally stimulated current. Most of the polypeptides were shown to possess both amorphous regions and segments of long-range order. Water, which interacts preferentially with the amorphous zones, behaves as plasticizer, i.e. facilitates the localized motions of polypeptide chains. The results obtained have been correlated with elastin elasticity, in particular as far as the fundamental destructuring role of water is concerned.

Conformational changes induced in α-elastin by cholesterol, taurocholate and unsaturated fatty acids

Abstract The ability of sodium taurocholate, cholesterol and oleic, linoleic and palmitoleic acids to induce conformational changes in α-elastin has been studied by circular dichroism. In addition, the influence of Ca 2+ ions has been investigated. The formation of inelastic structure (α-helix, β-form) in the protein has been evidenced by spectral data. These results could be of interest in relation to aging and atherogenesis.

Evidence of order in (Val-Pro-Gly)n, a repeating sequence of chick elastin

Poly(Val-Pro-Gly) was synthesized and its conformation in solution was investigated by circular dichroism. The results gave evidence for the presence of β-bend conformations, most probably of type II β-bend, stabilized by -CO ...NH- hydrogen bonds connecting the Vali and Vali + 3 residues along the amino acid sequence.

Human α-elastins: lipid-induced conformational changes

Abstract α-Elastins from young and old human aortas have been prepared and the interaction of these modified proteins with taurocholate, oleate, linoleate and palmitoleate has been studied by means of circular dichroism. Multiple conformational transitions were observed possibly involving, in addition to the aperiodic form, structures such as the β-bend and β-like forms. At the molecular level, a correlation between the aging of elastin and its interaction with lipids has been found that could be extended, at the macroscopic scale, to processes such as atherosclerosis and aging of the arterial wall.

Electron microscopic evidence for elastin-like supramolecular organization in synthetic polytripeptides

Electron microscope studies have been carried out on polytripeptides comprising the sequences -Pro-X-Gly- and -X-Pro-Gly- (X = Val, Ile, Met). These polymers have previously been shown to either contain or lack secondary structure. The formation of aligned filaments and also, in some cases, of banded fibers has been demonstrated. Independent of predicted solution conformation the supramolecular structures appeared to be very similar to those previously demonstrated for elastin and its soluble derivatives. The possibility that supramolecular organization is not a necessary consequence of molecular ordered structures is put forward and discussed. With respect to the molecular structure of elastin, the results suggest caution in the interpretation of electron microscope observation at the molecular scale.

Conformational studies on methionyl-containing diketopiperazines

Abstract Circular dichroism measurements on methionyl-containing diketopiperazines have shown that the thioether side chain favours the appearance of fold conformations in the ring. A solvent-dependent conformational distribution has been also found in the case of l -methionylglycine diketopiperazzine.

Synthesis and conformational studies of proline-containing tripeptides

Abstract Using tripeptides of the type Boc-Pro-X-Gly-OEt and Boc-X-Pro-Gly-OEt where X = Val, Leu, Ile, Nle we have studied the influence of the X residue on the stability of folded conformations, most probably the β-turn, in these peptides. In addition, the substitution Gly→β-Ala was also investigated. Our c.d. and i.r. studies show significant changes in β-turn stability depending on the nature and the position of X and on specific solute-solvent interactions.

On the Molecular and Supramolecular Structure of Elastin

Elastin, the protein responsible for elasticity in most tissues of vertebrates, displays peculiar aminoacid composition and primary sequence. Actually, about 90% of aminoacid residues are apolar, and quite unusual cross-links (desmosine and isodesmosine) [1] and many repetitive sequences are present [2–6]. the mature, insoluble protein originates from a soluble precursor called tropoelastin by posttranslational cross-linking. In recent years gene analysis has revealed the primary sequence of tropoelastins from different sources, such as the human [2], bovine [3],, chick [4], and murine [5] species. While these findings have considerably deepened our understanding of the elastin system, there are still several unanswered questions: is elastin a “classical” elastomer according to Flory theory [7] or not ?, is the supramolecular, fibrous structure of the protein determined by some preferred molecular conformation? Other questions concern the possible biological role played by specific sequences of elastin. In particular, tropoelastin itself and some peptides such as VGVAPG, AGVPGFGVG, GFGVGAGVP and GFGVG have been shown to possess chemotactic activity towards fibroblasts [8-10]. Interestingly, one of these peptides is a fragmentation product of elastase attack. Therefore, one wonders whether they could play a physiological and/or pathological role. in addition, recent studies have evidenced several immunogenic regions of the proteins including the chemotactic sequence VGVAPG [8,9]. Interestingly, this sequence is also chemotactic for certain tumor cell lines such as the M 27 line of the Lewis lung carcinoma [11]. One current approach toward elastin structure-function relationships has been based on investigations concerning synthetic models and fragments of the protein. As mentioned, the primary sequence of elastins is characterized by many repetitive sequences. The repetition, when cosidered in a statistical sense, can be found at different scales: at the lowest scale XGG and XPG (X=A, V, L, I) sequences are very frequently found, at the highest scale the entire protein has been interpreted as the repetition of few particular domains [4]. Given that, one can reasonably approach the problem of elastin structure through the synthesis of appropriate “monomers” and repeating polypeptides (polimers).