Search results for "Crystallization"
showing 10 items of 774 documents
Dimer-tetramer transition between solution and crystalline states of streptavidin and avidin mutants.
2003
ABSTRACT The biotin-binding tetrameric proteins, streptavidin from Streptomyces avidinii and chicken egg white avidin, are excellent models for the study of subunit-subunit interactions of a multimeric protein. Efforts are thus being made to prepare mutated forms of streptavidin and avidin, which would form monomers or dimers, in order to examine their effect on quaternary structure and assembly. In the present communication, we compared the crystal structures of binding site W→K mutations in streptavidin and avidin. In solution, both mutant proteins are known to form dimers, but upon crystallization, both formed tetramers with the same parameters as the native proteins. All of the intersub…
Molecular recognition in biotin-streptavidin systems and analogues at the air-water interface
1992
Abstract Specific interaction between biotin and the protein streptavidin in monolayers of synthetic lipids with biotin headgroups has been shown to lead to formation of highly ordered two-dimensional streptavidin crystals. The same behaviour is observed when using desthiobiotin as lipid headgroup which exhibits a significantly lower binding constant compared with biotin (5 × 10 13 M -1 compared with 10 15 M -1 ). This offers the possibility of detaching competetively the 2D crystalline streptavidin layer by addition of free biotin to the aqueous phase. Use of lipoic acid as lipid headgroup ( K a = 7 × 10 7 M −1 ) leads to formation of small snisotropic protein domains indicating a crystall…
Crystallization and preliminary X-ray analysis of W120K mutant of streptavidin.
2001
Bacterial streptavidin and chicken avidin are homotetrameric proteins that share an exceptionally high affinity towards the vitamin biotin. The biotin-binding sites in both proteins contain a crucial tryptophan residue contributed from an adjacent subunit. This particular tryptophan (W110 in avidin and W120 in streptavidin) plays an important role in both biotin binding and in the quaternary stabilities of the proteins. An intriguing naturally occurring alteration of tryptophan to lysine was previously described in the C-terminal domain of sea-urchin fibropellins, which share a relatively high sequence similarity with avidin and streptavidin. Avidin (Avm-W110K) and streptavidin (Savm-W120K)…
Functionalized lipid tubules as tools for helical crystallization of proteins
1997
The development of functional supramolecular devices built by self-assembly of elementary molecules and with bioactive properties arouses considerable interest in the field of nanotechnology and new materials. We report here the formation of a new class of lipid tubules exhibiting both properties of molecular recognition and crystal formation for the protein streptavidin. These lipid tubules, made of biotin-containing dioctadecylamine molecules, are straight hollow cylinders with a constant diameter of 27 nm and variable length up to several micrometers. They are unilamellar with an inner diameter of about 16 nm, as shown by cryoelectron microscopy. Streptavidin binds to the biotinylated tu…
Crystallization of SrCO3 on a self-assembled monolayer substrate: an in-situ synchrotron X-ray study
2001
Self-assembled monolayers (SAMs) of alkanethiols on gold surfaces show great promise in controlling the nucleation and growth of inorganic minerals from solution. In doing so, they mimic the role of some biogenic macromolecules in natural biomineralisation processes. Crystallization on SAM surfaces is usually monitored ex-situ; by allowing the process to commence and to evolve for some time, removing the substrate from the mother solution, and then examining it using microscopy, diffraction etc. We present here for the first time, the use of high energy monochromatic synchrotron X-radiation in conjunction with a two dimensional detector to monitor in situ, in a time resolved fashion, the gr…
Trapping Amorphous Intermediates of Carbonates – A Combined Total Scattering and NMR Study
2018
Crystallization via metastable phases plays an important role in chemical manufacturing, biomineralization, and protein crystallization, but the kinetic pathways leading from metastable phases to the stable crystalline modifications are not well understood. In particular, the fast crystallization of amorphous intermediates makes a detailed characterization challenging. To circumvent this problem, we devised a system that allows trapping and stabilizing the amorphous intermediates of representative carbonates (calcium, strontium, barium, manganese, and cadmium). The long-term stabilization of these transient species enabled a detailed investigation of their composition, structure, and morpho…
Structural and morphological rearrangements in quenched poly(ethylene) by simultaneous SAXS/WAXS
2000
Structure formation by crystallization from the melt in a wide range of cooling rates (0.08-1 000°C/s) in low-density polyethylene has been studied by simultaneous small- and wide-angle X-ray scattering at the synchroton radiation source of DESY. The occurrence of two periodicities, characterized by different angular position of Bragg's maxima, was observed, pointing to the existence of two types of lamellar stacks, associated with two different long period values L 1 and L 2 (L 1 > L 2 ). L 1 depends on the cooling rate, whereas L 2 is almost constant. A comparison with isotactic polypropylene is performed, where a similar phenomenon takes place. While in the case of i-PP a definite correl…
Dehydration and crystallization of trehalose and sucrose glasses containing carbonmonoxy-myoglobin
1999
We report a study wherein we contemporarily measured 1) the dehydration process of trehalose or sucrose glasses embedding carbonmonoxy-myoglobin (MbCO) and 2) the evolution of the A substates in saccharide-coated MbCO. Our results indicate that microcrystallization processes, sizeably different in the two saccharides, take place during dehydration; moreover, the microcrystalline structure is maintained unless the dry samples are equilibrated with a humidity >/=75% (>/=60%) at 25 degrees C for the trehalose (sucrose) sample. The evolution of the parameters that characterize the A substates of MbCO indicates that 1) the effects of water withdrawal are analogous in samples dried in the presenc…
Microscopy studies of the surface of high-temperature superconductor films
1997
The surface morphology is studied by use of optical and electron microscopes with respect to production regime (rate and temperature of crystallization) of the 50 - 125 micrometer thick doped YBa 2 Cu 3 O 7 films obtained by Stokes sedimentation on SrTiO 3 ceramic substrate (size 20 mm by 5 mm by 0.5 mm) and firing in air or oxygen following the MTG procedure, performed in the gradient tube furnace. Evolution of thick film structure with regard to temperature and cooling rate is studied.
Supercritical fluid crystallization of adipic acid using urea as habit modifier
2008
The crystal morphology of adipic acid mediated by the action of urea as additive has been investigated using the supercritical antisolvent precipitation (SAS). The process was performed using acetone and carbon dioxide as solvent and antisolvent, respectively. The effect of urea concentration in the liquid solution and of precipitation pressure on the crystal habit was investigated; the products were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and infrared spectrometry (FT-IR). Urea was found to be very effective in modifying the crystal habit of adipic acid from needle-like shape with a length of several hun…