The physical characteristics of neodymium iron boron magnets for tooth extrusion. (49/2747)

Impaction and non-eruption of teeth is a common problem encountered in orthodontics and many techniques have been proposed for the management of this condition. It has been advocated that a system utilizing magnets would supply a continuous, directionally sensitive, extrusive force, through closed mucosa and thus provide not only a physiological sound basis for successful treatment, but also reduce the need for patient compliance and appliance adjustment. This ex vivo investigation examined in detail the physical characteristics of neodymium iron boron magnets employed in attraction in order to assess their usefulness in the clinical situation. Attractive force and magnetic flux density measurements were recorded for nine sets of magnet pairs with differing morphologies. The effect of spatial relationship on force was assessed by varying vertical, transverse and horizontal positions of the magnets relative to each other, and by altering the pole face angles. The data obtained suggest that magnets with larger pole face areas and longer magnetic axes provide the best performance with respect to clinical usefulness. It was possible to formulate a specific relationship between force and flux density for each magnet pair. This relationship can be used in the clinical management of unerupted teeth to predict the force between the magnets by measuring the magnetic flux density present at mucosal level. The results indicate that magnetic systems may, indeed, have a place in the treatment of unerupted teeth.  (+info)

Interaction with GroEL destabilises non-amphiphilic secondary structure in a peptide. (50/2747)

The Escherichia coli molecular chaperone GroEL can functionally interact with non-native forms of many proteins. An inherent property of non-native proteins is the exposure of hydrophobic residues and the presence of secondary structure elements. Whether GroEL unfolds or stabilises these structural elements in protein substrates as a result of binding has been the subject of extended debate in the literature. Based on our studies of model peptides of pre-formed helical structure, we conclude that the final state of a GroEL-bound substrate is dependent on the conformational flexibility of the substrate protein and the distribution of hydrophobic residues, with optimal association when these are able to present a cluster of hydrophobic residues in the binding interface.  (+info)

Catalytic properties and conformation of hydrophobized alpha-chymotrypsin incorporated into a bilayer lipid membrane. (51/2747)

A set of artificially hydrophobized alpha-chymotrypsin derivatives, carrying 2-11 stearoyl residues per enzyme molecule, were synthesized and their catalytic parameters and conformation in water solution and in the liposome-bound state were investigated. Hydrophobization of alpha-chymotrypsin and its further incorporation into phosphatidylcholine (PC) liposomes have no effect on the rate constant of the N-acetyl-L-tyrosine ethyl ester (ATEE) ester bond hydrolysis (k(cat)). At the same time, an increase in the number of stearoyl residues attached to the enzyme results in a drastic decrease of ATEE binding to the active center (K(M) increase). Incorporation of the hydrophobized enzyme into the PC liposome membrane results in K(M) recovery to nearly that of native alpha-chymotrypsin. The above changes are accompanied by partial unfolding of the enzyme molecules observed by fluorescence measurements. The obtained results are of interest to mimic the contribution of surface hydrophobic sites in the functioning of membrane proteins.  (+info)

Discoupling the Ca(2+)-activation from the pore-forming function of the bi-component Panton-Valentine leucocidin in human PMNs. (52/2747)

The consecutive cell activation, including Ca(2+)-channel opening, and pore formation leading to human neutrophil lysis were the two functions of the staphylococcal Panton-Valentine leucocidin attempted to be discoupled by site-directed mutagenesis. In a first approach consisting in deletions of the cytoplasmic extremity of the transmembranous domain, we produced a LukF-PV DeltaSer125-Leu128 with a slightly reduced Ca(2+) induction but with a significantly lowered lytic activity when combined with its synergistic protein LukS-PV. The second approach consisted in the modification of charges and/or introduction of a steric hindrance inside the pore, which also led to interesting mutated proteins: LukF-PV G131D, G131W and G130D. The latter had an intact Ca(2+) induction ability while the lytic one was 20-fold diminished. Binding properties and intrinsic pore diameters of these discoupled toxins remained comparable to the wild-type protein. The mutated proteins promoted interleukin-8 secretion, but they were rather inactive in an experimental model. New insights are brought concerning the role of the two functions in the virulence of this bi-component leucotoxin.  (+info)

Cysteine-scanning mutagenesis around transmembrane segment VI of Tn10-encoded metal-tetracycline/H(+) antiporter. (53/2747)

Each amino acid in putative transmembrane helix VI and its flanking regions, from Ser-156 to Thr-185, of a Cys-free mutant of the Tn10-encoded metal-tetracycline/H(+) antiporter (TetA(B)) was individually replaced by Cys. All of the cysteine-scanning mutants showed a normal level of tetracycline resistance except for the S156C mutant, which showed moderate resistance, indicating that there is no essential residue located in this region. All 20 mutants from S159C to W178C showed no reactivity with N-ethylmaleimide (NEM), whereas the mutants of the flanking regions from S156C to H158C and F179C to T185C were highly or moderately reactive with NEM. These results indicate that like transmembrane helices III and IX, the transmembrane helix VI comprising residues Ser-159-Trp-178 is totally embedded in the hydrophobic environment.  (+info)

Protein hydration changes during catalysis: a new mechanism of enzymic rate-enhancement and ion activation/inhibition of catalysis. (54/2747)

There exists a linear correlation between the effect of a salt on the rate of an enzymic reaction and its effect on the activation volume (delta V++) of the reaction. Salts that increase delta V++ invariably decrease the rate of the reaction, and vice versa. The salt effects on reaction rate are, however, much larger than would be predicted solely on the basis of pressure-volume work changes deriving from the observed alterations in delta V++. Different inorganic salts affect reaction rates and activation volumes in a manner that reflects the salts' positions in the Hofmeister series. These observations, taken in conjunction with data on the effects of salts on protein functional group (aminoacid side-chains and peptide linkages) hydration, lead us to propose the following hypothesis to account for salt activation and inhibition of catalysis. Aminoacid side-chains and peptide linkages located on or near the protein surface change their exposure to water during conformational events in catalysis. These protein group transfers are accompanied by large volume and energy changes that are due largely to changes in the organization of water around these groups. When these transfer processes occur during the rate-limiting step in catalysis, these energy and volume changes can contribute to the free energy of activation (delta G++) and the activation volume of the reaction. By influencing the degree to which water can organize around transferred protein groups, salts can modify both the delta G++ (rate) and the delta V++ of a reaction.  (+info)

Rotation of F(1)-ATPase and the hinge residues of the beta subunit. (55/2747)

Rotation of a motor protein, F(1)-ATPase, was demonstrated using a unique single-molecule observation system. This paper reviews what has been clarified by this system and then focuses on the role of residues at the hinge region of the beta subunit. We have visualised rotation of a single molecule of F(1)-ATPase by attaching a fluorescent actin filament to the top of the beta subunit in the immobilised F(1)-ATPase, thus settling a major controversy regarding the rotary catalysis. The rotation of the beta subunit was exclusively in one direction, as could be predicted by the crystal structure of bovine heart F(1)-ATPase. Rotation at low ATP concentrations revealed that one revolution consists of three 120 degrees steps, each fuelled by the binding of an ATP to the beta subunit. The mean work done by a 120 degrees step was approximately 80 pN nm, a value close to the free energy liberated by hydrolysis of one ATP molecule, implying nearly 100% efficiency of energy conversion. The torque is probably generated by the beta subunit, which undergoes large opening-closing domain motion upon binding of AT(D)P. We identified three hinge residues, betaHis179, betaGly180 and betaGly181, whose peptide bond dihedral angles are drastically changed during domain motion. Simultaneous substitution of these residues with alanine resulted in nearly complete loss (99%) of ATPase activity. Single or double substitution of the two Gly residues did not abolish the ATPase activity. However, reflecting the shift of the equilibrium between the open and closed forms of the beta subunit, single substitution caused changes in the propensity to generate the kinetically trapped Mg-ADP inhibited form: Gly180Ala enhanced the propensity and Gly181Ala abolished the propensity. In spite of these changes, the mean rotational torque was not changed significantly for any of the mutants.  (+info)

Cross-linking and electron microscopy studies of the structure and functioning of the Escherichia coli ATP synthase. (56/2747)

ATP synthase, also called F(1)F(o)-ATPase, catalyzes the synthesis of ATP during oxidative phosphorylation. The enzyme is reversible and is able to use ATP to drive a proton gradient for transport purposes. Our work has focused on the enzyme from Escherichia coli (ECF(1)F(o)). We have used a combination of methods to study this enzyme, including electron microscopy and chemical cross-linking. The utility of these two approaches in particular, and the important insights they give into the structure and mechanism of the ATP synthase, are reviewed.  (+info)