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Giuseppe Falini

Publications and source records attributed to Giuseppe Falini.

15 recordsLinked to original sources
PubMed2006

Interaction of bovine serum albumin with chrysotile: spectroscopic and morphological studies.

The biodurability of chrysotile fibers, which is related to their cytotoxicity and mutagenic responses, is strongly affected by the surface chemical adsorption of biological molecules. Natural chrysotile is a heterogeneous material in both structure and composition. The availability of synthetic stoichiometric chrysotile of constant structure and uniform morphology has allowed us to investigate its interaction with bovine serum albumin (BSA). By using transmission electron microscopy (TEM) and atomic force microscopy (AFM), we have obtained the first morphological evidence of albumin adsorption onto chrysotile nanocrystals. FTIR spectroscopy was used to quantify modifications of BSA secondary structure that were induced by the surface interaction. The protein transition to beta-turns allows a stronger interaction between the protein hydrophilic side-chains and the charged asbestos surface, which is consistent with hydrogen bonds involving the superficial OH groups. Synthetic stoichiometric chrysotile nanocrystals were shown to be an ideal reference standard with which to study the interaction of asbestos fibers with biological systems, in order to elucidate the chemical mechanisms of asbestos toxicity.

Asbestos, Serpentine↗
PubMed2006

On the formation of amelogenin microribbons.

We recently reported the remarkable spontaneous self-assembly and hierarchical organization of amelogenin 'microribbons' and their ability to facilitate oriented growth of apatite crystals in vitro. In a letter of correction we communicated the finding that the X-ray diffraction pattern reported in our original report was that of cellulose contaminant and not amelogenin microribbon. We have re-evaluated our data and confirmed the protein nature of the microribbons using Fourier transform infrared and Raman microspectroscopy. Some microribbons were remarkably similar in their morphology to that of cellulose fibers. The size distribution of amelogenin microribbons was wider, particularly in width and length, and generally smaller than those originally reported. Here we present additional detailed information on the formation of a series of intermediate hierarchical structures of amelogenin assemblies prior to the formation of microribbon. The most significant finding was that full-length amelogenin nanospheres had a tendency to assemble into collinear arrays whose function is assumed to be critical at the initial stage of enamel mineral deposition. The present data gives an insight into the step-by-step assembly process of amelogenin from nanometer scale molecules to micrometer scale organized structures that can be used as templates for controlled and oriented growth of apatite mineralization in vitro.

Amelogenesis↗
PubMed2005

Supramolecular assembly of amelogenin nanospheres into birefringent microribbons.

Although both tooth enamel and bone are composed of organized assemblies of carbonated apatite crystals, enamel is unusual in that it does not contain collagen nor does it remodel. Self-assembly of amelogenin protein into nanospheres has been recognized as a key factor in controlling the oriented and elongated growth of carbonated apatite crystals during dental enamel biomineralization. We report the in vitro formation of birefringent microribbon structures that were generated through the supramolecular assembly of amelogenin nanospheres. These microribbons have diffraction patterns that indicate a periodic structure of crystalline units along the long axis. The growth of apatite crystals orientated along the c axis and parallel to the long axes of the microribbons was observed in vitro. The linear arrays (chains) of nanospheres observed as intermediate states before the microribbon formation give an important indication as to the function of amelogenin in controlling the oriented growth of apatite crystals during enamel mineralization.

Amelogenesis↗
PubMed2005

The 1.4 anstroms structure of dianthin 30 indicates a role of surface potential at the active site of type 1 ribosome inactivating proteins.

Ribosome inactivating proteins (RIPs) are plant proteins with enzymatic activity identified as rRNA N-glycosidase (EC 3.2.2.22), which cleaves the N-glycosidic bond of a specific adenine on the ricin/sarcin region of rRNA, thus causing inhibition of protein synthesis. They also depurinate extensively DNA and other polynucleotides. The three-dimensional structure of dianthin 30, a type 1 (single-chain) RIP of Dianthus caryophyllus (leaves), is now described at 1.4 angstroms, a resolution never achieved before for any RIP. The fold typical of RIPs is conserved, despite some differences in the loop regions. The general structure comparison by superimposed alpha-carbon (249 atoms) and the sequence alignment by structure for dianthin 30 and saporin-S6 give a root mean square deviation of 0.625 angstroms. Despite the differences reported for the biological activities of the two RIPs, their structures fit quite well and both show a protein segment containing strands beta7, beta8, and beta9 shorter than other RIPs. However, the surface electrostatic potential in the active site region neatly distinguishes dianthin 30 from saporin-S6. The possible relationship between the charge distribution and the behavior of the proteins toward different substrates is discussed.

Amino Acid Sequence↗
PubMed2004

Coenzyme site-directed mutants of photosynthetic A4-GAPDH show selectively reduced NADPH-dependent catalysis, similar to regulatory AB-GAPDH inhibited by oxidized thioredoxin.

Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher plants uses both NADP(H) and NAD(H) as coenzyme and consists of one (GapA) or two types of subunits (GapA, GapB). AB-GAPDH is regulated in vivo through the action of thioredoxin and metabolites, showing higher kinetic preference for NADPH in the light than in darkness due to a specific effect on kcat(NADPH). Previous crystallographic studies on spinach chloroplast A4-GAPDH complexed with NADP or NAD showed that residues Thr33 and Ser188 are involved in NADP over NAD selectivity by interacting with the 2'-phosphate group of NADP. This suggested a possible involvement of these residues in the regulatory mechanism. Mutants of recombinant spinach GapA (A4-GAPDH) with Thr33 or Ser188 replaced by Ala (T33A, S188A and double mutant T33A/S188A) were produced, expressed in Escherichia coli, and compared to wild-type recombinant A4-GAPDH, in terms of crystal structures and kinetic properties. Affinity for NADPH was decreased significantly in all mutants, and kcat(NADPH) was lowered in mutants carrying the substitution of Ser188. NADH-dependent activity was unaffected. The decrease of kcat/Km of the NADPH-dependent reaction in Ser188 mutants resembles the behaviour of AB-GAPDH inhibited by oxidized thioredoxin, as confirmed by steady-state kinetic analysis of native enzyme. A significant expansion of size of the A4-tetramer was observed in the S188A mutant compared to wild-type A4. We conclude that in the absence of interactions between Ser188 and the 2'-phosphate group of NADP, the enzyme structure relaxes to a less compact conformation, which negatively affects the complex catalytic cycle of GADPH. A model based on this concept might be developed to explain the in vivo light-regulation of the GAPDH.

Binding Sites↗
PubMed2004

Tubular-shaped stoichiometric chrysotile nanocrystals.

Stoichiometric chrysotile tubular nanocrystals have been synthesized as possible starting materials for applications toward nanotechnology, and as a standard reference sample for the investigation of the molecular interactions between chrysotile, the most utilized asbestos, and biological systems. Chrysotile nanocrystals have been synthesized under controlled hydrothermal conditions, and have been characterized by chemical, morphological, structural, spectroscopic and microcalorimetric analyses. They show a constant "cylinder-in-cylinder" morphology constituted by two or three concentric subunits. Each single nanocrystal has a tubular shape of about 49+/-1 nm in outer maximum diameter, and a hollow core of about 7+/-1 nm. Structural investigation carried out on an X-ray powder pattern allowed to improve the structural model proposed for chrysotile mineral samples. Synthetic chrysotile crystallizes in the monoclinic Cc space group with a=0.5340(1) nm, b=0.9241(1) nm, and c=1.4689(2) nm, beta=93.66(3) degrees.

Journal Article↗
PubMed2004

Effect of inorganic anions on the morphology and structure of magnesium calcite.

Calcium carbonate was precipitated from calcium hydroxide and carbonic acid solutions at 25 degrees C, with and without addition of different magnesium (MgSO(4), Mg(NO(3))(2) and MgCl(2)) and sodium salts (Na(2)SO(4), NaNO(3) and NaCl) of identical anions, in order to study the mode of incorporation of magnesium and inorganic anions and their effect on the morphology of calcite crystals over a range of initial reactant concentrations and limited c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios. The morphology, crystal size distribution, composition, structure, and specific surface area of the precipitated crystals, as well as the mode of cation and anion incorporation into the calcite crystal lattice, were studied by a combination of optical and scanning electron microscopy (SEM), electronic counting, a multiple BET method, thermogravimetry, FT-IR spectroscopy, X-ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. In the systems of high initial relative supersaturation, precipitation of an amorphous precursor phase preceded the formation of calcite, whereas in those of lower supersaturation calcite was the first and only polymorphic modification of calcium carbonate that appeared in the system. The magnesium content in calcite increased with the magnesium concentration in solution and was correlated with the type of magnesium salt used. Mg incorporation caused the formation of crystals elongated along the calcite c axis and, in some cases, the appearance of new [011] faces. Polycrystalline aggregates were formed when the c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios in solution were increased. Addition of sulfate ions, alone, caused formation of spherical calcite polycrystalline aggregates.

Journal Article↗
PubMed2003

Biologically inspired synthesis of bone-like composite: self-assembled collagen fibers/hydroxyapatite nanocrystals.

Replacement of bone tissue by graft materials and products of tissue engineering having composition, structure, and biological features that mimic natural tissue is a goal to be pursued. A biomimetic synthesis was performed to prepare new bone-like composites constituted of hydroxyapatite nanocrystals and self-assembled type I collagen fibers. We used a biological inspired approach that proved that the biological systems stored and processed information at the molecular level. Two different methodologies were used: dispersion of synthetic hydroxyapatite in telopeptides free collagen molecules solution and direct nucleation of hydroxyapatite into reconstituted collagen fibers during their assembling. The different preparation techniques were experimented then the composites thoroughly characterized and compared. Composite obtained by direct nucleation showed an intimated interaction of the inorganic and proteic components, which modified the apatitic phase and made its composition, morphology and structure similar to the mineral component of natural bone.

Bone Substitutes↗
PubMed2003

Crystallization and preliminary X-ray diffraction analysis of two ribosome-inactivating proteins: lychnin and dianthin 30.

Lychnin from the seeds of Lychnis chalcedonica and dianthin 30 from the leaves of Dianthus caryophyllus belong to the type 1 ribosome-inactivating proteins (RIPs). They have been crystallized by the vapour-diffusion method and the crystals diffracted to 1.7 and 1.3 A, respectively, using a synchrotron source. Lychnin and dianthin 30 crystals both belong to space group P2(1) with one protein chain in the asymmetric unit. The structure of dianthin 30 has been solved by molecular replacement using the coordinates of saporin-S6 as a model. The structure determination of lychnin, the sequence of which is not yet available, is in progress using the coordinates of other RIPs as models for molecular replacement.

Crystallization↗
PubMed2003

Dual coenzyme specificity of photosynthetic glyceraldehyde-3-phosphate dehydrogenase interpreted by the crystal structure of A4 isoform complexed with NAD.

Photosynthetic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of Spinacia oleracea belongs to a wide group of GAPDHs found in most organisms displaying oxygenic photosynthesis, including cyanobacteria, green and red algae, and higher plants. As a major catalytic difference with respect to glycolytic GAPDH, photosynthetic GAPDH exhibits dual cofactor specificity toward pyridine nucleotides with a preference for NADP(H). Here we report the crystal structure of NAD-complexed recombinant A(4)-GAPDH (NAD-A(4)-GAPDH) from Spinacia oleracea, expressed in Escherichia coli. Its superimposition onto native A(4)-GAPDH complexed with NADP (NADP-A(4)-GAPDH) pinpoints specific conformational changes resulting from cofactor replacement. In photosynthetic NAD-A(4)-GAPDH, the side chain of Asp32 is oriented toward the coenzyme to interact with the adenine ribose diol, similar to glycolytic GAPDHs (NAD-specific). On the contrary, in NADP-A(4)-GAPDH Asp32 moves away to accommodate the additional 2'-phosphate group of the coenzyme and to minimize electrostatic repulsion. Asp32 rotation is allowed by the presence of the small residue Ala40, conserved in most photosynthetic GAPDHs, replacing bulky amino acid side chains in glycolytic GAPDHs. While in NADP-A(4)-GAPDH two amino acids, Thr33 and Ser188, are involved in hydrogen bonds with the 2'-phosphate group of NADP, in the NAD-complexed enzyme these interactions are lacking. The crystallographic structure of NAD-A(4)-GAPDH highlights that four residues, Thr33, Ala40, Ser188, and Ala187 (Leu, Leu, Pro, and Leu respectively, in glycolytic Bacillus stearothermophilus GAPDH sequence) are of primary importance for the dual cofactor specificity of photosynthetic GAPDH. These modifications seem to trace the minimum evolutionary route for a primitive NAD-specific GAPDH to be converted into the NADP-preferring enzyme of oxygenic photosynthetic organisms.

Amino Acid Sequence↗
PubMed2002

Solvent-induced modulation of collective photophysical processes in fluorescent silica nanoparticles.

In this paper we show how it is possible to control the nature and the efficiency of collective photophysical processes in a network composed of two different fluorescent units organized on the surface of silica nanoparticles. Such a structure is obtained by covering nanoparticles with a layer of dansyl moieties (Dns) and by partially protonating them in solution. The two fluorophores Dns and Dns.H(+) have very different photophysical properties and can be selectively excited and detected. The interaction between the two units Dns and Dns.H(+) has been first investigated in a reference compound obtained by derivatizing 1,6-hexanediamine with two dansyl units. The photophysical characterization of this compound (absorption spectra, fluorescence spectra, quantum yield, and lifetime) showed that the two moieties can be involved both in energy and electron-transfer processes. Dansylated nanoparticles were prepared by modifying preformed silica nanoparticles with dansylated (3-aminopropyl)trimethoxysilane. Photophysical studies indicated that protonation has a dramatic effect on the fluorescence of the nanoparticles, leading to the quenching of both the protonated units and the surrounding nonprotonated ones. This amplified response to protonation, due to charge-transfer interactions, is solvent-dependent and is less efficient in pure chloroform with respect to acetonitrile/chloroform (5/1 v/v) mixtures. The reduced efficiency of the electron-transfer processes responsible for the quenching makes energy transfer competitive to such an extent that in pure chloroform excitation energy migration takes place from Dns.H(+) to Dns with great efficiency.

Journal Article↗
PubMed2002

Protein crystallisation on chemically modified mica surfaces.

Chemically modified mica sheets have been tested as heterogeneous nucleant surfaces for lysozyme, concanavalin A and thaumatin. Smooth mica surfaces with reduced hydrophilic properties and different density of ionisable groups have been prepared by a silanisation reaction using mixtures of n-propyltriethoxysilane and 3-aminopropyltriethoxysilane in different percentages starting from 0 to 100% of aminosilane. The crystallisation experiments were carried out with the hanging drop vapour diffusion technique. The results suggest that these mica surfaces act as heterogeneous nucleant agents, whose effectiveness is due to non-specific attractive and local interactions between charged residues of the protein and the ionisable groups on the mica surfaces.

Aluminum Silicates↗
PubMed2002

Crystallization of calcium carbonate salts into beta-chitin scaffold.

Composites of beta-chitin with calcium carbonate polymorphs were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The beta-chitin was obtained from the pen of the Loligo sp. squid. The three main polymorphs of calcium carbonate: aragonite, calcite and vaterite, were observed. Their location within the matrix is a function of the polymorph. The supersaturation inside the compartmentalized space in the chitin governs the location and polymorphism of the crystals.

Animals↗
PubMedDate not supplied

Chitin mineralization.

The polysaccharide chitin is found in nature as a major component of the organic fraction of several biocomposites in which an organic matrix is associated with an inorganic fraction. The relationship between the mineral phase and the organic phase implies a high level of molecular recognition. Chitin in mineralized biological systems is present in different polymorphs and has a crucial role in the hierarchical control of the biomineralization processes; the nacre of the mollusk shell is a representative example. Biologically inspired synthesis has been used for the production of mineral-chitin composites. Their actual and future applications move from the medical field as bone repair (chitin-calcium phosphate composites) to the industrial field as catalyst (silica chitin structure replica).

Biocompatible Materials↗