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Biomedical subjects

L Mazzarella

Publications and source records attributed to L Mazzarella.

70 records · Page 4Linked to original sources
PubMedDate not supplied

Crystal structure of a collagen-like polypeptide with repeating sequence Pro-Hyp-Gly at 1.4 A resolution: implications for collagen hydration.

The use of polypeptide models has proved to be a valuable tool to obtain accurate information on the collagen triple helix. Here we report the high resolution crystal structure of a collagen-like polypeptide with repeating sequence Pro-Hyp-Gly. The structure has been refined to an R(factor) of 0.137 and an R(free) of 0.163 using synchrotron diffraction data extending up to 1.4 A resolution. The polypeptide triple-helical structure binds a large number of water molecules, in contrast with a previous structure determination at lower resolution. The highly hydrated nature of this polypeptide confirms a number of previous studies conducted both in solution and in the crystal state. In addition, neighboring polypeptide triple helices are directly bound in the crystal through Hyp-Hyp hydrogen-bonding interactions. This finding supports the idea that Hyp residues may be important for the assembly of the triple helices in the collagen fibrils and may stabilize the fibrils by mediating direct contacts between neighboring molecules.

Amino Acid Sequence↗
PubMedDate not supplied

Mandible stabilization between ablative and reconstructive surgery.

The biphase external skeletal-fixation splint (Morris splint) for mandibular stabilization has been used in cases of ablative surgery. It is a practical approach to stabilization for patients whether or not they undergo reconstruction, either immediate or delayed. The Morris splint can be applied without increasing the time required for major resection. It can be left in place for prolonged periods, but it still allows easy surgical access and easy postoperative care and observation. While not a new tool, it has been little used by the head and neck cancer surgeon, probably because it has not been presented for this purpose but rather for treating fractures. A practical approach to the use of the Morris biphase splint is presented, as well as the indications for its use and some results of our experience with this tool.

Bone Screws↗
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↗