Two-loop Structure Research Articles

Hydrophobic Pairwise Interactions Stabilize α-Conotoxin MI in the Muscle Acetylcholine Receptor Binding Site

The present work delineates pairwise interactions underlying the nanomolar affinity of alpha-conotoxin MI (CTx MI) for the alpha-delta site of the muscle acetylcholine receptor (AChR). We mutated all non-cysteine residues in CTx MI, expressed the alpha(2)betadelta(2) pentameric form of the AChR in 293 human embryonic kidney cells, and measured binding of the mutant toxins by competition against the initial rate of (125)I-alpha-bungarotoxin binding. The CTx MI mutations P6G, A7V, G9S, and Y12T all decrease affinity for alpha(2)betadelta(2) pentamers by 10,000-fold. Side chains at these four positions localize to a restricted region of the known three-dimensional structure of CTx MI. Mutations of the AChR reveal major contributions to CTx MI affinity by Tyr-198 in the alpha subunit and by the selectivity determinants Ser-36, Tyr-113, and Ile-178 in the delta subunit. By using double mutant cycles analysis, we find that Tyr-12 of CTx MI interacts strongly with all three selectivity determinants in the delta subunit and that deltaSer-36 and deltaIle-178 are interdependent in stabilizing Tyr-12. We find additional strong interactions between Gly-9 and Pro-6 in CTx MI and selectivity determinants in the delta subunit, and between Ala-7 and Pro-6 and Tyr-198 in the alpha subunit. The overall results reveal the orientation of CTx MI when bound to the alpha-delta interface and show that primarily hydrophobic interactions stabilize the complex.

PID Robust Model Following Control

Abstract The paper deals with properties of a two-loop structure of PID control system containing the nominal model of controlled plant and two PID controllers. The special attention is paid to high robustness of considered control structure to the perturbations of the controlled plant in relation to its nominal model and to disturbances commonly met in industrial practice. The results of simulations confirm high robustness of the considered control structure. Owing to its advantages, the proposed structure of control may find wide application in new implementation of PID to robust control of the parameter-varying process plants.

Structural Elements in α-Conotoxin ImI Essential for Binding to Neuronal α7 Receptors

The neuronal-specific toxin alpha-conotoxin ImI (CTx ImI) has the sequence Gly-Cys-Cys-Ser-Asp-Pro-Arg-Cys-Ala-Trp-Arg-Cys-NH2, in which each cysteine forms a disulfide bridge to produce a constrained two-loop structure. To investigate the structural basis for bioactivity we mutated individual residues in CTx ImI and determined bioactivity. Bioactivity of the toxins was determined by their competition against 125I-labeled alpha-bungarotoxin binding to homomeric receptors containing alpha7 sequence in the major extracellular domain and 5HT-3 sequence elsewhere. The results reveal two regions in CTx ImI essential for binding to the alpha7/5HT-3 receptor. The first is the triad Asp-Pro-Arg in the first loop, where conservative mutations of each residue diminish affinity by 2-3 orders of magnitude. The second region is the lone Trp in the second loop, where an aromatic side chain is required. The overall results suggest that within the triad of the first loop, Pro positions the flanking Asp and Arg for optimal interaction with one portion of the binding site, while within the second loop, Trp stabilizes the complex through its aromatic ring.

A CURRENT RIBBON MODEL FOR ENERGY STORAGE AND RELEASE WITH APPLICATION TO THE FLARE OF 7 JANUARY 1992

Observations of the flare on 7 January 1992 are interpreted using a topological model of the magnetic field. The model, developed here, applies a theory of three-dimensional reconnection to the inferred magnetic field configuration for 7 January. In the model field a new bipole (∼ 1021 Mx) emerges amidst pre-existing active region flux. This emergence gives rise to two current ribbons along the boundaries (separators) separating the distinct, new and old, flux systems. Sudden reconnection across these boundary curves transfers ∼ 3 ×1020 Mx of flux from the bipole into the surrounding flux. The model also predicts the simultaneous (sympathetic) flaring of the two current ribbons. This explains the complex two-loop structure noted in previous observations of this flare. We subject the model predictions to comparisons with observations of the flare. The locations of current ribbons in the model correspond closely with those of observed soft X-ray loops. In addition the footpoints and apexes of the ribbons correspond with observed sources of microwave and hard X-ray emission. The magnitude of energy stored by the current ribbons compares favorably to the inferred energy content of accelerated electrons in the flare.

Mixing input-output pseudolinearization and gain scheduling techniques for stabilization of mobile robots with two independently driven wheels

In this paper, we propose a two-loop structure to transform and stabilize the kinematic model of a nonholonomic mobile robot with two independently driven wheels. This two-loop structure consists of input-output pseudolinearization and gain scheduling techniques. A comparison with previous methods is included. The main contribution of this paper is to apply a input-output pseudolinearization transformation method and to use an effective pole-assignment strategy for stabilizing a mobile robot with two independently driven wheels. The proposed method has demonstrated superiority over previous methods.

High yield fermentation and purification of Tendamistat disulphide analogues secreted by Streptomyces lividans.

In our studies of structure-function correlation of polypeptides we used Tendamistat (TM), an alpha-amylase-inhibitor of Streptomyces tendae, as a model to investigate the influence of different mutants on the expression and secretion of the protein. In addition, we examined the influence of replacing the two disulphide-bridges that stabilize the two-loop structure of the whole protein. The single mutants C27S, C27T, C45A, the double mutants C11A/C27A, C11A/C27S, C11A/C27T, C11A/C27L, C45/C73A and the fourfold mutant C11A/C27A/C45A/C73A were prepared. The mutated TM gene was expressed in S. lividans TK 24, which secretes the active form of the inhibitor into the culture medium. Compared with the wild-type, the double-mutated TM derivatives show an increase in secreted protein by a factor of two to ten. In contrast, the single-mutated inhibitor analogues show the reverse effect. In order to examine the influence of temperature and culture media on the production of protein derivative we used the most unstable C11A analogue. Our expression studies at 10, 19, 28 and 37 degrees C established 19 degrees C as the optimal temperature for production of the protein derivatives. The correlation between the stability and secretion of TM is discussed in the context of our knowledge of protein translocation in bacteria. Based on these experiments we optimized the fermentation parameters, isolated TM analogous on a large scale, and verified them.