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L Mazzarella

Publications and source records attributed to L Mazzarella.

At least 37 records · Page 2Linked to original sources
PubMed1998

Activation of diketopiperazine formation by alkylammonium carboxylate salts and aprotic dipolar protophobic solvents.

Diketopiperazine formation from the N-terminal residues of a peptide chain is accelerated by aprotic dipolar protophobic solvents and catalyzed in organic solvents by alkylammonium carboxylate salts. The t1/2 for the first-order reaction of H-Ala-Pro-NH2 x TFA falls from 20 d in methanol to 3.6 min in acetonitrile containing 0.02 mol dm(-3) triethylammonium acetate; for H-Ala-Ala-NH2 x TFA in the same reaction media t1/2 falls from an unmeasurably long time to 1.3 d.

Diketopiperazines↗
PubMed1996

BS-RNase tetramers: an example of domain-swapped oligomers.

In the ribonuclease superfamily, dimericity is a unique feature of bovine seminal RNase (BS-RNase). In about two-thirds of native BS-RNase molecules, the two subunits interchange their N-terminal tails, thus generating domain-swapped dimers (MxM), which mostly responsible for enzyme biological activities and allostericity. Higher molecular weight BS-RNase oligomers can also be prepared [Libonati, M. (1969) Ital. J. Biochem. 18, 407-417.]. This paper reports on BS-RNase tetrameric derivatives which were isolated and enzymatically characterized. The data collected and the analysis of the crystal packing of MxM dimers suggested a structural model for tetramer assembly, in which the four subunits are enchained by multiple domain-swapping events.

Binding Sites↗
PubMed1996

Deamidation in proteins: the crystal structure of bovine pancreatic ribonuclease with an isoaspartyl residue at position 67.

The non-enzymatic deamidation of asparagine residues in proteins is a widely occurring reaction, both in vivo and in vitro. Although the importance of this process is commonly recognised, only little structural information is available on it. In order to evaluate the structural effects of this reaction in proteins, we have determined the crystal structure of a ribonuclease A derivative in which asparagine 67 has been replaced by an isoaspartyl residue, as a consequence of an in vitro deamidation reaction. The overall structure of the model, refined to a crystallographic R-factor of 0.159 at a resolution of 1.9 A, is very similar to that of the native protein, but considerable deviations are observed in the region delimited by the disulphide bridge 65-72. In particular, the insertion of an extra methylene group in the main chain at residue 67 breaks up the hydrogen bond network that makes this region rather rigid in ribonuclease A. On the basis of the structure observed, some of the slightly but significantly different properties of this deamidated derivative, with respect to the native enzyme, can be explained.

Animals↗
PubMed1996

Kinetics and mechanism of the cleavage of the peptide bond next to asparagine.

The spontaneous cleavage reaction of the tetra-peptide Piv-Gly Asn-Sar-Gly-NHtBu to the C-terminal dipeptide and N-terminal succinimide dipeptide proceeds through pre-equilibrium deprotonation of the amide group of the asparagine side chain, followed by intramolecular nucleophilic attack of nitrogen on the peptide carbonyl carbonyl carbon atom. General acid-catalyzed breakdown of the intermediate then gives the products. According to this mechanism, the reaction rate strongly increases with pH and buffer concentration.

Asparagine↗
PubMed1995

Swapping structural determinants of ribonucleases: an energetic analysis of the hinge peptide 16-22.

Bovine seminal ribonuclease (BS-RNase) is a homodimeric enzyme strictly homologous to the pancreatic ribonuclease (RNase A). Native BS-RNase is an equilibrium mixture of two distinct dimers differing in the interchange of the N-terminal segments and in their biological properties. The loop 16-22 plays a fundamental role on the relative stability of the two isomers. Both the primary and tertiary structures of the RNase A differ substantially from those of the seminal ribonuclease in the loop region 16-22. To analyze the possible stable conformations of this loop in both enzymes, structure predictions have been attempted, according to a procedure described by Palmer and Scheraga [Palmer, K. A. & Scheraga, H. A. (1992) J. Comput. Chem. 13, 329-350]. Results compare well with experimental x-ray structures and clarify the structural determinants that are responsible for the swapping of the N-terminal domains and for the peculiar properties of BS-RNase. Minimal modifications of RNase A sequence needed to form a stable swapped dimer are also predicted.

Animals↗
PubMed1995

Folding of aminosuccinyl peptides: thermodynamic data from temperature dependent circular dichroism measurements.

The conformational equilibrium of aminosuccinyl peptides between extended conformations and an intramolecularly hydrogen bonded type II' beta-turn conformation has been studied on the peptide Boc-L-Asu-Gly-L-Ala-OMe (Asu = aminosuccinyl residue) by means of temperature dependence of circular dichroism spectra. Owing to the peculiar chiroptical and conformational properties of the Asu residue, this technique proved to be very useful for deriving thermodynamic data for the above folding process. The value of delta H0 (-6.6 kJ mol-1), obtained for the peptide studied in a chloroformacetonitrile mixture, shows that the lower energy of the folded conformer is primarily due to the characteristic intramolecular hydrogen bond of the beta turns.

Amino Acid Sequence↗
PubMed1995

Acid catalysis in the formation of dioxopiperazines from peptides containing tetrahydroisoquinoline-3-carboxylic acid at position 2.

The kinetics of the spontaneous formation of 2,5-dioxopiperazines from peptides containing the Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) residue in the 2-position of the sequence has been studied in DMSO and water solution. The reaction is first order in Tic-peptide and subject to general-acid catalysis. Moreover, only the fraction of peptide having the amino terminal group in the deprotonated state reacts with appreciable rate. In pure organic solvent, and in aqueous solution with low buffer concentration, the degradation reaction of Tic-peptides is very low; at 20 degrees C for the peptide H-Tyr-Tic-Phe-Phe-NH2, in DMSO and in neutral water in the absence of buffer, the half-lives (t1/2) are 3 x 10(4) and 1.2 x 10(4) h, respectively. The addition of carboxylic acids or buffers to the reaction solutions markedly increases the reaction rate; in 0.01 m HAc in DMSO and in 0.1 M phosphate buffer in water, pH 7.1, t1/2 values for the tetrapeptide are 61 and 121 h, respectively.

Acids↗
PubMed1994

Crystallization and preliminary X-ray analysis of the river buffalo (Bubalus bubalis L.) BB phenotype carbonmonoxyhaemoglobin.

Ruminant haemoglobin (Hb) extracted from river buffalo (Bubalus bubalis) has been purified and crystallized. Two different Hb forms of the phenotype BB gave isomorphous crystals which diffracted to 2.8 A resolution and were not sensitive to radiation damage. Crystals of CO Hb have space group P2(1)2(1)2(1) with unit-cell parameters a = 54.8, b = 64.0, c = 158.6 A, and contain one Hb molecule per asymmetric unit.

Journal Article↗
PubMed1993

Bovine seminal ribonuclease: structure at 1.9 A resolution.

The crystal structure of bovine seminal ribonuclease, a homodimeric enzyme closely related to pancreatic ribonuclease, has been refined at a nominal resolution of 1.9 A employing data collected on an electronic area detector. The final model consists of two chains containing 1990 non-H atoms, seven sulfate anions and 113 water molecules per asymmetric unit. The unit-cell parameters are a = 36.5 (1), b = 66.7 (1) and c = 107.5 (2) A, space group P22(1)2(1). The R factor is 0.177 for 16 492 reflections in the resolution range 6.0-1.9 A and the deviations from ideal values of bond lengths and bond angles are 0.020 A and 3.7 degrees, respectively. The molecule is formed by two pancreatic like chains, which have their N-terminal segments interchanged so that each active site is formed by residues from both subunits. The two chains are related by a non-crystallographic twofold symmetry and are covalently linked by two consecutive disulfide bridges, which form an unusual sixteen-membered ring across the dimer interface. The deviations from the molecular symmetry, the hydration shell and the sulfate-binding sites are also discussed in relation to the known structure of the pancreatic enzyme.

Journal Article↗
PubMed1993

Selective deamidation of ribonuclease A. Isolation and characterization of the resulting isoaspartyl and aspartyl derivatives.

Selective deamidation of proteins and peptides is a reaction of great interest, whether it has physiological significance as in protein aging, or occurs as a disturbing event in the preparation of natural or recombinant proteins. Deamidation of bovine pancreatic ribonuclease A, RNase A, a classical model protein, has been reported to occur only after denaturation of the protein, or under harsh conditions. In this paper convenient procedures are described for selective deamidation of Asn67 in native RNase A under mild conditions. Furthermore, for the first time, both products of deamidation were isolated: the aspartyl and the isoaspartyl containing protein derivatives. Replacement of Asn67 with either residue lowers the catalytic activity of the enzyme, on RNA and on model substrates, except when a dinucleotide with a purine on the 5' side is the substrate. In the latter case an intriguing increase in the specificity constant is observed. The Asp67 derivative was found to refold, after full denaturation and reduction, at the same rate as the fully amidated protein, whereas the iso-Asp67 derivative refolded at half that rate. It is hypothesized that this effect is due to a delayed formation of disulfide 65-72 for the presence of the abnormal isopeptide bond between residues 67 and 68.

Amino Acid Sequence↗
PubMed1993

Crystallization and preliminary X-ray analysis of an NAD(+)-dependent alcohol dehydrogenase from the extreme thermophilic archaebacterium Sulfolobus solfataricus.

An NAD(+)-dependent alcohol dehydrogenase from the extreme thermophilic archaebacterium Sulfolobus solfataricus has been crystallized in the holo-enzyme and apo-enzyme forms. Crystals of the holo-enzyme grow from 2-methyl-2,4-pentanediol at pH 8.4 with the addition of NADH and at pH 7.0 with the addition of NADH and dimethyl sulphoxide. Crystals of the apo-enzyme grow at pH 6.3 from a mixture of polyethylene glycol 4000 and propan-2-ol. The holo-enzyme crystallizes in C2 with a dimer in the asymmetric unit, however the crystals are twinned and unsuitable for data collection. The apo-enzyme crystallizes in I4(1)22 (a = 126.82 A, b = 118.95 A) with a monomer in the asymmetric unit, and the single crystals diffract to 2.8 A.

Alcohol Dehydrogenase↗
PubMed1992

Solid-state conformations of aminosuccinyl peptides: structure of tert-butyloxycarbonyl-L-prolyl-L-aminosuccinyl-glycyl-L-alanine methyl ester (Boc-L-Pro-L-Asu-Gly-L-Ala-OMe). A case of pseudo-translational symmetry.

C20H30N4O8, M(r) = 454.48, monoclinic, P2(1), a = 13.411 (2), b = 12.592 (2), c = 14.710 (1) A, beta = 104.30 (1) degrees, V = 2407 (6) A3, Z = 4, Dx = 1.254 Mg m-3, lambda (Cu K alpha) = 1.5418 A, mu = 0.783 mm-1, F(000) = 968, room temperature, final R = 0.086, wR = 0.080 for 4055 observed reflections. The title compound is a model for the intermediate formed in the deamidation reaction of porcine adrenocorticotropin hormone. The structure presents a pseudo-translational symmetry and was solved by using a modified version of the SIR88 package. In the refinement, few stereochemical restraints were needed to handle the static disorder shown by the C-terminal fragment of one molecule in the asymmetric unit. The conformation of the two independent molecules is almost identical and is a II' beta-bend, stabilized by an intramolecular hydrogen bond. In the crystal, screw-related molecules are linked by hydrogen bonds. The two molecules in the independent unit are related by the translation vector u = 0.4962 (2)a + 0.7310 (2)b + 0.5075 (2)c.

Amino Acid Sequence↗
PubMed1992

Histopathology of spontaneous brain herniations into the middle ear.

Two patients with spontaneous brain herniation into the middle ear have been operated on with a combined otoneurological approach. In case No. 1, two 2 x 3 mm arachnoid tissue herniations were found in the tegmen antri of the left ear. Six years later, a 8 x 9 mm mass consisting of prolapsed brain was removed from the right ear. The histological examination showed normal but disorganized nervous tissue. The surface consisted of middle ear mucosa or modified glial cells. More deeply numerous well preserved neurons and synapses were observed. In case No. 2, a 2 x 1 cm herniation was found in contact with the ossicles and the bony walls of the middle ear. The herniation consisted of partly degenerated nervous tissue which could explain the episode of temporal lobe seizure the patient experienced 8 years before surgery. In the world literature during the last 40 years, 29 cases of spontaneous or idiopathic brain herniation into the middle ear and mastoid have been reported. In 10, the herniations were multiple, as in our case No. 1. Case No. 1 is interesting also because the spontaneous brain herniation was bilateral.

Cerebrospinal Fluid Otorrhea↗
PubMed1992

[Desmoid tumors of the abdominal wall].

The authors report their experience in the management of desmoid tumors, rare benign neoplasias, locally aggressive and potentially recurrent after surgery. Etiopathogenetic, diagnostic, and therapeutic features of these tumors are analysed and the value of surgery as well as chemo- or radiotherapy is considered.

Abdominal Muscles↗
PubMed1989

Solid-state conformations of aminosuccinyl peptides: crystal structure of tert-butyloxycarbonyl-L-leucyl-L-aminosuccinyl-L-phenylalaninami de.

The protected tripeptide tert-butyloxycarbonyl-L-leucyl-L-aminosuccinyl-L-phenylalaninamide crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 6.214(3), b = 12.832(3), c = 33.094(4) A, Z = 4. The structure was solved by direct methods using MULTAN 80 and refined to an R value of 0.055 for 1458 reflections. The bond lengths and angles are in good agreement with the standard values. The peptide backbone adopts a type II' beta-bend conformation with a weak intramolecular hydrogen bond between the CO group of the leucyl residue and the C-terminal NH2 group. In agreement with previous studies, this structure confirms the high propensity of aminosuccinyl peptides to adopt a type II' beta-bend conformation. The role of this conformation in relation to the deamidation process in proteins is also discussed.

Models, Molecular↗
PubMed1988

N-benzyloxycarbonyl-L-aminosuccinyl-L-phenylalaninamide (Z-L-Asu-L-Phe-NH2).

C21H21N3O5, Mr = 395.42, orthorhombic, P2(1)2(1)2(1), a = 5.935 (2), b = 13.037 (1), c = 25.992 (2) A, V = 2011 (1) A3, Z = 4, D chi = 1.31 Mg m-3, lambda(Cu K alpha) = 1.5418 A, mu = 0.74 mm-1, F(000) = 832, room temperature, final R = 0.046 for 1343 observed reflections. The title compound adopts a type II' beta-turn conformation in the solid state, stabilized by a 4----1 intramolecular hydrogen bond between the CO of the protecting benzyloxycarbonyl group and the NH2 of the terminal amide group. These results indicate that the beta-turn conformation, already found in the solid state for peptides embodying the sequence Asu-Gly or Asu-Ala, is highly preferred, even when the residue next to the aminosuccinyl moiety has a bulkier side chain. In the crystal, rows of hydrogen-bonded molecules are held together by van der Waals forces between hydrophobic phenyl groups.

Dipeptides↗
PubMed1986

The role of the subfornical organ in the drinking behavior of the pigeon.

Pigeons with radiofrequency lesions that damaged the subfornical organ (SFO) (n = 4) or that isolated it from adjacent structures (n = 5), but not sham-lesioned pigeons, were unresponsive to blood-borne (i.p.) ANG II (100 micrograms/pigeon) in the immediate postoperative period and for 60 days thereafter. These animals were less sensitive to hypovolemic challenge (20% PEG), but they responded normally to 24 h of water deprivation and to cellular dehydration. Despite their unresponsiveness to bloodborne ANG II, the lesioned pigeons drank normally to 10 ng of i.c.v. ANG II given as early as 10 days after surgery, and they drank reliably and vigorously but less in total volume to 100 ng i.c.v. They also drank quickly, vigorously, and in normal total volume to i.c.v. tachykinins and bombesins, and to the peripheral (i.p.) bombesins. Peripheral (i.m.) tachykinins produced only low volume and variable drinking in all birds tested regardless of brain damage. The SFO of the pigeon, like that of the mammal, is essential for drinking evoked by blood-borne ANG II and is not necessary for thirst aroused by ANG II acting from within the cerebral ventricles. Lastly, it does not mediate the dipsogenic effects of the tachykinins or the bombesins.

Angiotensin II↗