Showing papers by "Paolo Mariani published in 1999"

The structural basis for the regulation of tissue transglutaminase by calcium ions

Abstract: The role of calcium ions in the regulation of tissue transglutaminase is investigated by experimental approaches and computer modeling. A three-dimensional model of the transglutaminase is computed by homology building on crystallized human factor XIII and is used to interpret structural and functional results. The molecule is a prolate ellipsoid (6.2 x 4.2 x 11 nm) and comprises four domains, assembled pairwise into N-terminal and C-terminal regions. The active site is hidden in a cleft between these regions and is inaccessible to macromolecular substrates in the calcium-free form. Protein dynamics simulation indicates that these regions move apart upon addition of calcium ions, revealing the active site for catalysis. The protein dimensions are consistent with results obtained with small-angle neutron and X-ray scattering. The gyration radius of the protein (3 nm) increases in the presence of calcium ions (3.9 nm), but it is virtually unaffected in the presence of GTP, suggesting that only calcium ions can promote major structural changes in the native protein. Proteolysis of an exposed loop connecting the N-terminal and C-terminal regions is linearly correlated with enzyme inactivation and prevents the calcium-induced conformational changes.

Salt-Induced Association of β-Lactoglobulin by Light and X-ray Scattering

Abstract: β-Lactoglobulin, a protein belonging to the lipocaline family, is studied by Photon correlation spectroscopy and small angle X-ray scattering in acidic solutions (pH = 2.3) and at ionic strengths in the range 7−507 mM. Both experiments give a clear evidence of a protein monomer−dimer equilibrium affected by the ionic strength of the solution. The interparticle interactions are determined by means of Photon correlation spectroscopy by following the trend of the protein diffusion coefficient versus concentration (from 0.2 to 25 g/L) at ionic strengths of 7 and 107 mM. From a detailed analysis, estimates of the protein charge, hydrodynamic radius, and dimeritazion fraction have been obtained. Small angle X-ray scattering measurements performed versus ionic strength (from 7 to 507 mM) in dilute solutions (10 g/L) allow an independent estimate of the dimerization fraction. A global fit of the SAXS scattered intensities at different salt concentrations using a simple electrostatic model for the aggregation mech...

Stabilization of the monoolein Pn3m cubic structure on trehalose glasses

Abstract: Trehalose is known to protect some organisms from various stresses due to drought and high temperature. To explore the molecular mechanism of the protective function, the mesomorphic properties of the monoolein-water system, dried in the presence of trehalose, were studied by X-ray diffraction. While, in pure water, two bicontinuous inverse cubic structures (the Pn3m and Ia3d phases) and a lamellar Lα phase exist as a function of concentration, only the Pn3m cubic phase has been detected in concentrated trehalose solutions or in trehalose glasses, even under extremely dry conditions. Depending on the sugar concentration, or after glass dehydration, the Pn3m cubic unit cell decreases to very low values, much below the smaller one observed in pure water. However, as no phase transitions occur, a simple osmotic mechanism can be excluded. An additional stabilization of the lipid phase, arising from interfacial free energy changes due to trehalose-water-lipid direct interactions, and large enough to affect the energetic balance between the Pn3m and the Ia3d cubic phases, evidently occurs. Moreover, no differences in the Pn3m cubic structure were observed when the sugar platelets convert to the glassy state; no apparent structural modifications that can be related to mechanical pressure exerted on the lipid phase have been detected.

A new lyotropic liquid crystalline phase formed in hydrocarbon solvents by a deoxyguanosine derivative through extensive hydrogen bonding

Abstract: Lipophilic deoxyguanosine 1 in pure hydrocarbons or in mixed CHCl3-hydrocarbon solvents forms a new lyotropic liquid crystalline phase characterized by a two dimensional square packing. The structural elements of the phase are ribbon-like assembled species which are completely different from the columnar structures, based on G-quartets, which are the building blocks of the mesophases formed by deoxyguanosine oligonucleotides in water.

The Self‐Assembly of a Lipophilic Deoxyguanosine Derivative and the Formation of a Liquid‐Crystalline Phase in Hydrocarbon Solvents.

Abstract: The lipophilic 3′,5′-di-O-decanoyl-2′-deoxyguanosine (1) in CHCl3 undergoes extensive self-assembly, mediated by H-bonding between the guanine bases, to give ribbon-like aggregates. X-Ray investigation of the platelets obtained from CHCl3 reveals a disordered fibre-like structure consisting of stacks of the ribbon-like aggregates. The aggregates are completely different from the columnar structures, based on G-quartets, which are the building blocks of the mesophases formed by deoxyguanosine oligonucleotides in H2O. In pure hydrocarbons or in CHCl3/hydrocarbons, 1 forms a lyotropic liquid-crystalline phase.