Structures of unliganded and inhibitor complexes of W168F, a loop6 hinge mutant of Plasmodium falciparum Triosephosphate Isomerase: observation of an intermediate position of loop6

The enzymatic reaction of triosephosphate isomerase (TIM) is controlled by the movement of a loop (loop6, residues 166-176). Crystal structures of TIMs from a variety of sources have revealed that the loop6, which is in an open conformation in the unliganded enzyme, adopts a closed conformation in inhibitor complexes. In contrast, structures with loop open conformation are obtained in most of the complexes of TIM from the malarial parasite Plasmodium falciparum (PfTIM). W168 is a conserved N-terminal hinge residue, involved in different sets of interactions in the "open" and "closed" forms of loop6. The role of W168 in determining the loop conformation was examined by structural studies on the mutant W168F and its complexes with ligands. The three-dimensional structures of unliganded mutant (1.8 Å) and complexes with sulfate (2.8 Å) and glycerol-2-phosphate (G2P) (2.8 Å) have been determined. Loop6 was found disordered in these structures, reflecting the importance of W168 in stabilizing either the open or the closed states. Critical sequence differences between the Plasmodium enzyme and other TIMs may influence the equilibrium between the closed and open forms. Examination of the environment of the loop6 shows that its propensity for the open or the closed forms is influenced not only by Phe96 as suggested earlier, but also by Asn233, which occurs in the vicinity of the active site. This residue is Gly in the other TIM sequences and probably plays a crucial role in the mode of ligand binding, which in turn affects the loop opening/closing process in PfTIM

Aggregation of apolar peptides in organic solvents. Concentration dependence of <SUP>1</SUP>H-nmr parameters for peptide NH groups in 3<SUB>10</SUB> helical decapeptide fragment of suzukacillin

Peptide NH chemical shifts and their temperature dependences have been monitored as a function of concentration for the decapeptide, Boc-Aib-Pro-Val-Aib-Val-Ala-Aib-Ala-Aib-Aib-OMe in CDCl3(0.001-0.06M) and (CD3)2SO (0.001-0.03M). The chemical shifts and temperature coefficients for all nine NH groups show no significant concentration dependence in (CD3)2SO. Seven NH groups yield low values of temperature coefficients over the entire range, while one yields an intermediate value. In CDCl3, the Aib(1) NH group shows a large concentration dependence of both chemical shift and temperature coefficient, in contrast to the other eight NH groups. The data suggest that in (CD3)2SO, the peptide adopts a 310 helical conformation and is monomeric over the entire concentration range. In CDCl3, the 310 helical peptide associates at a concentration of 0.01M, with the Aib(1) NH involved in an intermolecular hydrogen bond. Association does not disrupt the intramolecular hydrogen-bonding pattern in the decapeptide

Structure of triosephosphate isomerase (TIM) from Methanocaldococcus jannaschii

The crystal structure of a recombinant triosephosphate isomerase (TIM) from the archaeabacterium Methanocaldococcus jannaschii has been determined at a resolution of 2.3 Å using X-ray diffraction data from a tetartohedrally twinned crystal. M. jannaschii TIM (MjTIM) is tetrameric, as suggested by solution studies and from the crystal structure, as is the case for two other structurally characterized archaeal TIMs. The archaeabacterial TIMs are shorter compared with the dimeric TIMs; the insertions in the dimeric TIMs occur in the vicinity of the tetramer interface, resulting in a hindrance to tetramerization in the dimeric TIMs. The charge distribution on the surface of the archaeal TIMs also facilitates tetramerization. Analysis of the barrel interactions in TIMs suggests that these interactions are unlikely to account for the thermal stability of the archaeal TIMs. A novelty of the unliganded structure of MjTIM is the complete absence of electron density for the loop 6 residues. The disorder of this loop could be ascribed to a missing salt bridge between residues at the N- and C-terminal ends of the loop in MjTIM

Structural chemistry and membrane modifying activity of the fungal polypeptides zervamicins, antiamoebins and efrapeptins

The fungal polypeptides zervamicins, antiamoebins and efrapeptins have been fractionated into several polypeptide components by HPLC. A zervamicin fraction lacking tryptophan has been characterized and shown to possess an N-terminal leucine residue. The conformations of zervamicin IIA and a synthetic analog in solution are compared with those determined for the related peptide, antiamoebin. The results are consistent with a completely helical structure for the apolar analog of zervamicin in chloroform, with partial unfolding in dimethylsulfoxide. A similar conformation has been determined for natural zervamicin IIB. A synthetic analog of efrapeptin forms a continuous helix in apolar solvents while, partial unfolding is seen in polar solvents. Natural zervamicin is an effective uncoupler of mitochondrial oxidative phosphorylation. Significant differences in membrane modifying activity are noted for the natural peptide and the synthetic apolar analog of zervamicin

Influence of Rolling and Ageing On Mechanical Properties of AA2195 Based Metal Matrix Composites

The modern Aluminium based composites have a great demand in the field of aerospace applications due to their lightweight, high strength, high stiffness, and superior mechanical properties. The main objective is to fabricate the AA2195 composites through Medium Frequency Induction Furnace (MFIF) with Taguchi L16 design of experiments, hot rolling process and heat treatment of composites is done and then compare the mechanical properties of hot rolled and heat treated AA2195 composite with casted composite. It is analyzed the effects of reinforcements like graphite and boron carbide on the mechanical behaviors and microstructure of both AA2195 composites. The microstructures revealed that reinforcements were distributed uniformly throughout the composites. It observed that the elemental investigation on SEM and XRD for both the composites showed that formed intermetallic compounds (IMCs) helped refine the microstructure and further increased the mechanical properties. The hot rolled and heat-treated AA2195 composite fabricated at 8% B4C and 6% Gr exhibits the more enhanced ultimate tensile strength, hardness, and reduction in density, % elongation compared to the casted composite. The rolling process is used to reduce the porosity of the composite. In contrast, heat treatment enhances the composite's mechanical properties like strength and hardness

Ionophore-mediated transmembrane movement of divalent cations in small unilamellar liposomes: an evaluation of the chlortetracycline fluorescence technique and correlations with black lipid membrane studies

Conceptual advances in the field of membrane transport have, in the main, utilized artificial membranes, both planar and vesicular. Systems of biological interest, viz., cells and organelles, resemble vesicles in size and geometry. Methods are, therefore, required to extend the results obtained with planar membranes to liposome systems. In this report we present an analysis of a fluorescence technique, using the divalent cation probe chlortetracycline, in small, unilamellar vesicles, for the study of divalent cation fluxes. An ion carrier (X537 A) and a pore former (alamethicin) have been studied. The rate of rise of fluorescence signal and the transmembrane ion gradient have been related to transmembrane current and potential, respectively. A second power dependence of ion conduction-including the electrically silent portion thereof - on X537 A concentration, has been observed. An exponential dependence of "current" on "transmembrane potential" in the case of alamethicin is also confirmed. Possible errors in the technique are discussed

Disulfide luminescence. Emission characteristics of cyclic tetrapeptide disulfides

Luminescence has been detected in cyclic tetrapeptide disulfides containing only nonaromatic residues. Excitation of the -S-S- n-&#963;&#8727;, filled transition between 280 and 290 nm leads to emission in the region 300-340 nm. The position and intensity of the emission band depends on the stereochemistry of the peptide and polarity of the solvent. Quantum yields ranging from 0.002 to 0.026 have been determined. Disulfide luminescence is quenched by oxygen and enhanced in solutions saturated with nitrogen. Contributions from disulfide linkages should be considered, when analysing the emission spectra of proteins, lacking tryptophan but having a high cystine content

Influence of Rolling and Ageing On Mechanical Properties of AA2195 Based Metal Matrix Composites

The modern Aluminium based composites have a great demand in the field of aerospace applications due to their lightweight, high strength, high stiffness, and superior mechanical properties. The main objective is to fabricate the AA2195 composites through Medium Frequency Induction Furnace (MFIF) with Taguchi L16 design of experiments, hot rolling process and heat treatment of composites is done and then compare the mechanical properties of hot rolled and heat treated AA2195 composite with casted composite. It is analyzed the effects of reinforcements like graphite and boron carbide on the mechanical behaviors and microstructure of both AA2195 composites. The microstructures revealed that reinforcements were distributed uniformly throughout the composites. It observed that the elemental investigation on SEM and XRD for both the composites showed that formed intermetallic compounds (IMCs) helped refine the microstructure and further increased the mechanical properties. The hot rolled and heat-treated AA2195 composite fabricated at 8% B4C and 6% Gr exhibits the more enhanced ultimate tensile strength, hardness, and reduction in density, % elongation compared to the casted composite. The rolling process is used to reduce the porosity of the composite. In contrast, heat treatment enhances the composite's mechanical properties like strength and hardness

Spermidine as a potential biosynthetic precursor to the 1,5-diazabicyclo[4:3:0]nonene residue in the efrapeptins

Efrapeptins (1±3