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Piera Valenti

Publications and source records attributed to Piera Valenti.

24 records · Page 2Linked to original sources
PubMed2002

The expression of the dodecameric ferritin in Listeria spp. is induced by iron limitation and stationary growth phase.

The Gram-positive bacterium Listeria innocua possesses an authentic ferritin with an unusual dodecameric assemblage that resembles the quaternary structure of the DNA-binding proteins designated Dps (DNA-binding proteins from starved cells). The L. innocua gene encoding the above protein, termed ferritin from Listeria innocua (fri), has been localized on a 3-kb HindIII chromosomal fragment cloned in the Escherichia coli strain DH5alphaF'. DNA sequence analysis reveals an open reading frame of 468 nucleotides matching perfectly the amino acid sequence of the protein. Primer extension analysis indicates the presence of two transcriptional startpoints located 36 (proximal) and 85 nt (distal) upstream the fri start codon, respectively. Each transcriptional startpoint is preceded by suitably located -10 and -35 elements, which match the sigma(A) (proximal) and sigma(B) (distal) consensus sequences.In L. innocua and Liseria monocytogenes, fri expression increases both upon entry into stationary phase and, more markedly, under low-iron growth conditions. The effect of iron is apparent in the exponential and stationary phases of growth. An up-regulation by iron limitation has never been observed in other proven ferritins and bacterioferritins, but has been reported for several members of the Dps family. The unusual regulation by iron of the Listeria ferritin gene provides further support to the evolutionary link with the Dps family and suggests that the iron storage function may not be the unique role of ferritin in the physiology of this bacterium.

Amino Acid Sequence↗
PubMed2002

Antiadenovirus activity of milk proteins: lactoferrin prevents viral infection.

Different milk proteins were analysed for their inhibitory effect on adenovirus infection in vitro. Proteins investigated were mucin, alpha-lactalbumin, beta-lactoglobulin, bovine lactoferrin, and human lactoferrin. Results obtained demonstrated that mucin, alpha-lactalbumin, and beta-lactoglobulin did not prevent the viral cytopathic effect, whereas lactoferrin was able to inhibit adenovirus replication in a dose-dependent manner. Further experiments were carried out in which lactoferrin was added to the cells during different phases of viral infection. Results obtained showed that lactoferrin was able to prevent viral replication when added both before, or during the viral adsorption step, or when present during the entire replicative cycle of adenovirus, demonstrating that its action takes place on an early phase of viral replication.

Adenovirus Infections, Human↗
PubMed2002

Antiviral activity of ovotransferrin discloses an evolutionary strategy for the defensive activities of lactoferrin.

Ovotransferrin (formerly conalbumin) is an iron-binding protein present in birds. It belongs to the transferrin family and shows about 50% sequence homology with mammalian serum transferrin and lactoferrin. This protein has been demonstrated to be capable of delivering iron to cells and of inhibiting bacterial multiplication. However, no antiviral activity has been reported for ovotransferrin, although the antiviral activity of human and bovine lactoferrins against several viruses, including human herpes simplex viruses, has been well established. In this report, the antiviral activity of ovotransferrin towards chicken embryo fibroblast infection by Marek's disease virus (MDV), an avian herpesvirus, was clearly demonstrated. Ovotransferrin was more effective than human and bovine lactoferrins in inhibiting MDV infection and no correlation between antiviral efficacy and iron saturation was found. The observations reported here are of interest from an evolutionary point of view since it is likely that the defensive properties of transferrins appeared early in evolution. In birds, the defensive properties of ovotransferrin remained joined to iron transport functions; in mammals, iron transport functions became peculiar to serum transferrin, and the defensive properties towards infections were optimised in lactoferrin.

Animals↗
PubMed2002

Ca2+ binding to bovine lactoferrin enhances protein stability and influences the release of bacterial lipopolysaccharide.

Bovine lactoferrin (bLf) is known to damage the outer membrane of Gram-negative bacteria by binding to bacterial lipopolysaccharide (LPS). We report that LPS is released from bacterial outer membranes also when apo- or metal-saturated Lf is separated from bacterial cells by a dialysis membrane. This process occurs in phosphate-buffered saline with no added Ca2+ and Mg2+ and is hindered by addition of these cations. The effect of bLf is similar to that induced by EDTA and has been ascribed to chelation of Ca2+. In fact, it may be envisaged that Ca2+-binding sites on LPS have different affinities and that bLf can remove those ions that are more weakly bound. Ca2+ binding does not alter Lf iron-binding properties significantly or its UV and CD spectral features but brings about changes in the FT-IR bands due to carboxylate residues. Ca2+ binding is characterized by an apparent dissociation constant of 6 microM and a stoichiometry of 1.55 Ca2+ per Lf molecule; it enhances bLf stability towards chemical and thermal denaturation. The increase in stability takes place in both the apo- and iron-saturated forms but not in the desialilated protein, indicating that the carboxylate groups of the sialic acid residues present on two of the glycan chains are involved in Ca2+ binding.

Animals↗
PubMed2002

Anti-invasive activity of bovine lactoferrin towards group A streptococci.

Group A streptococci (GAS) are able to invade cultured epithelial and endothelial cells without evidence of intracellular replication. GAS, like other facultative intracellular bacterial pathogens, evolved such ability to enter and to survive within host cells avoiding the host defences, and bacterial intracellular survival could explain the recurrence of infections. We report here that 1 mg bovine lactoferrin (bLf)/mL significantly hindered the in vitro invasion of cultured epithelial cells by GAS isolated from patients suffering from pharyngitis and completely inhibited the invasiveness of GAS pretreated with subinhibiting concentrations of erythromycin or ampicillin. One milligram of bLf per millilitre was also able to increase the number of epithelial cells undergoing apoptosis following GAS invasion, although the number of intracellular GAS in the presence of bLf decreased by about 10-fold. The ability of bLf to decrease GAS invasion was confirmed by an in vivo trial carried out on 12 children suffering from pharyngitis and already scheduled for tonsillectomy. In tonsil specimens from children treated for 15 days before tonsillectomy with both oral erythromycin (500 mg t.i.d. (three times daily)) and bLf gargles (100 mg t.i.d.), a lower number of intracellular GAS was found in comparison with that retrieved in tonsil specimens from children treated with erythromycin alone (500 mg t.i.d.).

Animals↗