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M Paci

Publications and source records attributed to M Paci.

83 records · Page 5Linked to original sources
PubMed1983

High resolution 1H-n.m.r. study of the interaction between initiation factor IF1 and 30S ribosomal subunits.

Interaction between Escherichia coli translational initiation factor IF1 (mol. wt. 8119) and 30S ribosomal subunits was followed by high resolution 1H-n.m.r. spectroscopy. Upon gradual addition of increasing yet largely sub-stoichiometric amounts of biologically active deuterated 30S ribosomal subunits, selective line broadenings and chemical shift changes were observed against the background of the gradual disappearance of the whole spectrum. At the highest 30S:IF1 ratio attained (0.25), all the resonance lines were broadened beyond meaningful detection. This behaviour, which can be partly reversed by increasing the ionic strength and/or the temperature, is due to the interaction between IF1 and the 30S ribosomal subunits, and can be explained by the existence of a medium-fast exchange dynamics between free and bound factor. The selective effects observed during titration with 30S ribosomal subunits shed some light on the mode of interaction of IF1 with 30S ribosomal subunits. At least one of the two His residues of the factor appears to be involved in the binding, since it undergoes a low-field change of chemical shift and becomes totally immobilized in the IF1-30S complex. Also strongly implicated in the interaction with 30S are more than one Ser and Arg residue and probably one lysine. Additional effects of the interaction of IF1 with ribosomes are a drastic reduction in the intensity of the ring current upfield shifted methyl resonances and mobilization of a previously rotationally hindered phenylalanine ring.

Escherichia coli↗
PubMedDate not supplied

Identification of a conserved N-capping box important for the structural autonomy of the prion alpha 3-helix: the disease associated D202N mutation destabilizes the helical conformation.

Peptides corresponding to three alpha helices present in the C-terminal region of the human prion protein have been synthesized and their structural autonomy analyzed by circular dichroism (CD) and NMR spectroscopy. The results obtained indicate that the protein fragment corresponding to the alpha 3-helix, in contrast to alpha 1 and alpha 2 peptides, shows a complete structural autonomy. The chemical shifts values found for NH and CHalpha resonance of the isolated alpha 3 peptide, formed by 30 aminoacid residues, were markedly and surprisingly similar to the corresponding values of the alpha 3-helix in the protein. The structural autonomy of the alpha 3-helix is profoundly determined by the presence of the conserved capping box and, in part, by the ionic bond formed between Glu200 and Lys204. On the basis of these observations a novel PrP consensus pattern, centered on the alpha 3-helix region, has been defined. The data indicate that this autonomous and highly conserved region of the PrPc likely plays a critical role in folding and stability. This gives an explanation of why many of pathogenic mutations occur in this part of the molecule, sharing relevant effects on the overall protein conformation. In particular the D202N capping mutation almost completely destabilizes the isolated alpha 3 peptide. While it is well known that the D202N substitution is associated with a GSS disease, the possible structural basis of this fatal pathology has never been investigated. We propose that a lower alpha 3-helical propensity leading to a major destabilization of the PrPc molecule initiates the pathogenic process associated with D202N capping mutation.

Amino Acid Sequence↗
PubMedDate not supplied

Combined effects of an oxidative enzyme and dissolved humic substances on 13C-labelled 2,4-D herbicide as revealed by high-resolution 13C NMR spectroscopy.

Phenoxyalkanoic acids are a widely used class of herbicides. This work employed high-resolution 13C NMR to study the structural changes induced by humic substances and horseradish perodixase on 2,4-dichlorophenoxyacetic acid (2,4-D) 13C-labelled in the side chain. NMR spectra showed that humic substances chemically catalyze abiotic splitting of [13C]2,4-D into 2,4-dichlorophenol and [13C]acetic acid at pH 7 but not at pH 4.7. Peroxidase did not catalyze the oxidative degradation of [13C]2,4-D at any pH tested and inhibited the effect of humic substances. Catalytic degradation by humic substances was attributed to free-radical reactions enhanced by the stereochemical contribution of large conformational structures formed by heterogeneous humic molecules at neutral pH. Inhibition of 2,4-D degradation when humic substances were combined with peroxidase was explained by modification of both chemical and conformational humic structure due to peroxidase-promoted oxidative cross-coupling among humic molecules. Our findings show for the first time that the abiotic degradation of 2,4-D is catalyzed by dissolved humic substances at neutral pH.

2,4-Dichlorophenoxyacetic Acid↗
PubMedDate not supplied

Evaluation of N parameter in the staging of non-small cell lung cancer: role of CT and PET.

PURPOSE: To determine diagnostic accuracy of CT and FDG-PET for the evaluation of N status in non-small cell lung cancer. MATERIALS AND METHODS: Thirty-eight CT scans and PET scans of patients with non small-cell lung cancer were retrospectively reviewed. The data of the noninvasive techniques about N status were compared with the pathology findings obtained by standard lymphadenectomy. RESULTS: The CT results were concordant with surgery in 24 out of 38 cases (63%); in discordant cases CT understaged 8 patients and overstaged 6. The PET images were concordant with surgery in 29 cases (76%); of the remaining 9, PET understaged 5 cases and overstaged 4. Concerning the N parameter, CT had a sensitivity of 42.8% and a specificity of 83.3%, while PET had a sensitivity of 71.4% and a specificity of 91.6%. CONCLUSIONS: In our experience the diagnostic accuracy of PET is superior to that of CT, in agreement with the most important studies in the literature. On only one occasion did PET fail to differentiate between hilar uptake (N1) and the central primary tumour, an area in which CT provided more precise anatomic details. Nonetheless, we believe that PET should be performed in all patients affected by lung cancer, with the only exception of patients shown to be not suitable for surgery after CT examination.

Journal Article↗