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S Capasso

Publications and source records attributed to S Capasso.

32 records · Page 2Linked to original sources
PubMed1984

Type II' beta-bend conformation of tert.-butyloxycarbonyl-L-amino-succinyl-L-alanyl-glycine methyl ester in the solid state.

Boc-L-Asu-L-Ala-Gly-OMe crystallizes in the monoclinic space group P2(1) with cell dimensions a = 14.315 (3) A, b = 9.280 (2) A, c = 14.358(3) A, beta = 103.63(1) A, V= 1853.4 (9) A3, with two molecules in the asymmetric unit. The conformation of the two molecules is characterized by a type II' beta-bend, similar to that predicted earlier by potential energy calculations, stabilized by an intramolecular hydrogen bond. I.r. and 1H-n.m.r. data show that the folded conformation is also stable in chloroform solution.

Formic Acid Esters↗
PubMedDate not supplied

Formation of an RNase A derivative containing an aminosuccinyl residue in place of asparagine 67.

At acidic pH, Asp67 and beta-Asp67 (beta-Asp: isoaspartic acid residue) derivatives of RNase A, obtained by selective deamidation of the parent enzyme, spontaneously produces a new derivative containing an aminosuccinyl residue (Asu). The overall secondary structure of the protein chain does not change as a consequence of this substitution, while the catalytic activity on RNA is reduced to about 25%. The pH dependence of the first-order rate constants for the Asu formation has a bell-shaped profile, the maximum being close to the pK(a) of the aspartic acid side chains. Moreover, the values of the rate constants are of the same magnitude of those measured for Asp-containing peptides whose sequence mimics the Asu formation site of the enzyme. This feature indicates that Asp67 and beta-Asp67 residues in the deamidated RNase A derivatives are sited in a region flexible enough to permit the cyclization of the carboxylic side chain to succinimide ring. These results are discussed at the light on to the three-dimensional structure and the thermodynamic stability of the aspartic acid derivatives of RNase A.

Amino Acid Sequence↗
PubMedDate not supplied

Conformation of aminosuccinyl dipeptides Ac-L-X-L-Asu-NMe from empirical energy calculations.

The aminosuccinyl (Asu) residue is formed as intermediate in some peptide and protein reactions. Potential energy calculations, using the parameters of the empirical conformational energy program for peptides (ECEPP), were performed on blocked X-Asu dipeptides, where X = Gly, Ala, Ser, Val and Pro. Results indicate that intra-residue interactions are dominant, and the low-energy dipeptide conformations correspond to the low-energy single-residue minima. Comparisons were made with previous results from energy calculations on blocked Asu-X dipeptides (X = Gly, Ala, Ser and Val).

Dipeptides↗
PubMedDate not supplied

Deamidation via cyclic imide of asparaginyl peptides: dependence on salts, buffers and organic solvents.

The deamidation reaction of Asn side chain was studied in the presence of the chemicals usually used at high concentration in the purification and crystallization of peptides and proteins. All the experiments were performed on the model peptide Boc-L-Asn-Gly-Gly-NH2. The pathway of the reaction is not affected by the medium used; in all cases it proceeds through a succinimide intermediate giving a mixture of isoaspartyl and aspartyl peptide. However, the rate of the reaction significantly depends on the solvent: the addition of organic solvents to an aqueous solution of the peptide has the general effect of decreasing the reaction rate, which, on the other hand, is strongly enhanced by a high concentration of organic and inorganic buffers. Only a minor influence is exerted by aprotic salts and polyethylene glycol.

Amides↗
PubMedDate not supplied

Conformation of aminosuccinyl dipeptides Ac-Asu-X-NHMe from empirical energy calculations.

Conformational energy calculations were carried out on the N-acetyl-N'-methylamides of aminosuccinyl (Asu) peptides. Computations were performed using a procedure analogous to that of the ECEPP/2 program, on N-Ac-L-Asu-NMe, N-Ac-L-Asu-L-X-NHMe, where X = Gly, Ala, Ser, Val and N-Ac-D-Asu-L-Ala-NHMe. With the exception of N-Ac-L-Asu-L-Val-NHMe, the lowest-energy forms of all the dipeptides correspond to a beta-bend conformation of type II' or II for a L,L and D,L sequence, respectively. When X = Val, the folded conformation is destabilized, and more extended conformations are preferred. The puckering of the cyclic imide has a small but meaningful influence on the relative energies of the minima. The calculations were shown to be in agreement with available experimental data.

Dipeptides↗
PubMedDate not supplied

Deamidation via cyclic imide in asparaginyl peptides.

The deamidation reaction of asparaginyl peptides was studied as a function of the pH and sequence. The deamidation of Boc-Asn-Gly-Gly-NH2 and the hydrolysis of the corresponding aminosuccinyl (Asu) peptide, Boc-Asu-Gly-Gly-NH2, were carried out in the pH ranges 5-10, whereas the deamidation of Boc-Asn-Ala-Gly-NH2, Boc-Asn-Gly-Ala-NH2 and Boc-Asn-Ser-Gly-NH2 was studied at pH 8.9 only. In each case, the conversion of the amide side-chain moiety of the Asn to carboxyl group occurs via a succinimide intermediate (Asu), and its breakdown leads to a normal and an isoaspartyl peptide. The kinetic constants of the Asu formation and the hydrolytic step increase markedly at basic pH. The influence of the side chain of the residue next to Asn is also discussed.

Amides↗
PubMedDate not supplied

[Erythrohemophagocytic lymphohistiocytosis. A clinical report of 3 cases].

Three infants suffering from hepatosplenomegaly, pancytopenia, hyperlipidemia, low fibrinogen levels and fever are reported. Two patients died during the first year of life, the third one received allogenic bone transplantation and survives. Clinical and haematological features are consistent with diagnosis of hemophagocytic lymphohistiocytosis.

Bone Marrow Transplantation↗