Refolding of riboflavin carrier protein as probed by biochemical and immunological parameters

The unfolding of the chicken egg white riboflavin carrier protein by disulfide reduction with dithiothreitol led to aggregation with concomitant loss of ligand binding characteristics and the capacity to interact with six monoclonal antibodies directed against surface-exposed discontinuous epitopes. The reduced protein could, however, bind to a monoclonal antibody recognizing sequential epitope. Under optimal conditions of protein refolding, the vitamin carrier protein regained its folded structure with high efficiency with simultaneous complete restoration of hydrophobic flavin binding site as well as the epitopic conformations exposed at the surface in a manner comparable to its native form.

The Folding Mechanism of Barstar: Evidence for Multiple Pathways and Multiple Intermediates

The mechanism of folding of the small protein barstar in the pre-transition zone at pH 7, 25 degrees C has been characterized using rapid mixing techniques. Earlier studies had established the validity of the three-state U-S reversible arrow U-F reversible arrow N mechanism for folding and unfolding in the presence of guanidine hydrochloride (GdnHCl) at concentrations greater than 2.0 M, where U-S and U-F are the slow-refolding and fast-refolding unfolded forms, respectively, and N is the fully folded form. It is now shown that early intermediates, I-S1 and I-S2 as well as a late native-like intermediate, I-N, are present on the folding pathways of U-S, and an early intermediate I-F1 on the folding pathway of U-F, when bars tar is refolded in concentrations of GdnHCl below 2.0 M. The rates of formation and disappearance of I-N, and the rates of formation of N at three different concentrations of GdnHCl in the pre-transition zone have been measured. The data indicate that in 1.5 M GdnHCl, I-N is not fully populated on the U-S --> I-S1 --> I-N --> N pathway because the rate of its formation is so slow that the U-S reversible arrow U-F reversible arrow N pathway can effectively compete with that pathway. In 1.0 M GdnHCl, the U-S --> I-S1 --> I-N transition is so fast that I-N is fully populated. In 0.6 M GdnHCl, I-N appears not to be fully populated because an alternative folding pathway, U-S --> I-S2 --> N, becomes available for the folding of U-S, in addition to the U-S --> I-S1 --> I-N --> N pathway Measurement of the binding of the hydrophobic dye 1-anilino-8-naphthalenesulphonate (ANS) during folding indicates that ANS binds to two distinct intermediates, I-M1 and I-M2, that form within 2 ms on the U-S --> I-M1 --> I-S1 --> I-N --> N and U-S --> I-M2 --> I-S2 --> N pathways. There is no evidence for the accumulation of intermediates that can bind ANS on the folding pathway of U-F.

Evaluation of strain-rate effects in transitional round jets using direct numerical simulation

The coherent flame model uses the strain rate to predict reaction rate per unit flame surface area and some procedure that solves for the dynamics of flame surfaces to predict species distributions. The strainrate formula for the reaction rate is obtained from the analytical solution for a flame in a laminar, plane stagnation point flow. Here, the formula's effectiveness is examined by comparisons with data from a direct numerical simulation (DNS) of a round jetlike flow that undergoes transition to turbulence. Significant differences due to general flow features can be understood qualitatively: Model predictions are good in the braids between vortex rings, which are present in the near field of round jets, as the strain rate is extensional and reaction surfaces are isolated. In several other regions, the strain rate is compressive or flame surfaces are folded close together. There, the predictions are poor as the local flow no longer resembles the model flow. Quantitative comparisons showed some discrepancies. A modified, consistent application of the strain-rate solution did not show significant changes in the prediction of mean reaction rate distributions.

Structural studies of protein unfolding

Methods for macromolecular structure determination (NMR and crystallography) are now being used to get structural information on partially folded and unfolded states of proteins. These techniques, in combination with proton hydrogen exchange studies are powerful tools to extract information on non-native states of proteins. This review discusses progress In this area of protein folding.

Nematogens with more flexible chains than aromatic rings in the core

Mesogens containing four rings in the main core can accommodate one terminal and two nearby lateral chains on each outside aromatic ring. These compounds containing six chains present an enantiotropic nematic range which is influenced by the rigidity of the links. The conformational behaviour of the first methyleneoxy group within the chains was investigated by one and two dimensional C-13 NMR. The sign of the jump in chemical shifts when entering the nematic phase indicates the folding of each lateral branch. Dipolar oscillations during cross-polarization contact provide the values of the bond order parameter. The two First lateral fragments do not behave in the same way, demonstrating the influence of the fragment along which the chain is back: folded.

Resent radar observations of asteroid 1566 Icarus

We report Doppler-only radar observations of Icarus at Goldstone at a transmitter frequency of 8510 MHz (3.5 cm wavelength) during 8-10 June 1996, the first radar detection of the object since 1968. Optimally filtered and folded spectra achieve a maximum opposite-circular (OC) polarization signal-to-noise ratio of about 10 and help to constrain Icarus' physical properties. We obtain an OC radar cross section of 0.05 km(2) (with a 35% uncertainty), which is less than values estimated by Goldstein (1969) and by Pettengill et al. (1969), and a circular polarization (SC/OC) ratio of 0.5+/-0.2. We analyze the echo power spectrum with a model incorporating the echo bandwidth B and a spectral shape parameter it, yielding a coupled constraint between B and n. We adopt 25 Hz as the lower bound on B, which gives a lower bound on the maximum pole-on breadth of about 0.6 km and upper bounds on the radar and optical albedos that are consistent with Icarus' tentative QS classification. The observed circular polarization ratio indicates a very rough near-surface at spatial scales of the order of the radar wavelength. (C) 1999 Elsevier Science Ltd. All rights reserved.

On the diversity and complexity of Zero Forcing receivers for MIMO Zero Padded systems

Zero padded systems with linear receivers are shown to be robust and amenable to fast implementations in single antenna scenarios. In this paper, properties of such systems are investigated when multiple antennas are present at both ends of the communication link. In particular, their diversity and complexity are evaluated for precoded transmissions. The linear receivers are shown to exploit multipath and receive diversities, even in the absence of any coding at the transmitter. Use of additional redundancy to improve performance is considered and the effect of transmission rate on diversity order is analyzed. Low complexity implementations of Zero Forcing receivers are devised to further enhance their applicability.

Robust Relay Precoder Design for MIMO-Relay Networks

In this paper, we consider a robust design of MIMO-relay precoder and receive filter for the destination nodes in a non-regenerative multiple-input multiple-output (MIMO) relay network. The network consists of multiple source-destination node pairs assisted by a single MIMO-relay node. The source and destination nodes are single antenna nodes, whereas the MIMO-relay node has multiple transmit and multiple receive antennas. The channel state information (CSI) available at the MIMO-relay node for precoding purpose is assumed to be imperfect. We assume that the norms of errors in CSI are upper-bounded, and the MIMO-relay node knows these bounds. We consider the robust design of the MIMO-relay precoder and receive filter based on the minimization of the total MIMO-relay transmit power with constraints on the mean square error (MSE) at the destination nodes. We show that this design problem can be solved by solving an alternating sequence of minimization and worst-case analysis problems. The minimization problem is formulated as a convex optimization problem that can be solved efficiently using interior-point methods. The worst-case analysis problem can be solved analytically using an approximation for the MSEs at the destination nodes. We demonstrate the robust performance of the proposed design through simulations.

Performance analysis of single-symbol maximum likelihood decodable linear STBCs

Performance of space-time block codes can be improved using the coordinate interleaving of the input symbols from rotated M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) constellations. This paper is on the performance analysis of coordinate-interleaved space-time codes, which are a subset of single-symbol maximum likelihood decodable linear space-time block codes, for wireless multiple antenna terminals. The analytical and simulation results show that full diversity is achievable. Using the equivalent single-input single-output model, simple expressions for the average bit error rates are derived over flat uncorrelated Rayleigh fading channels. Optimum rotation angles are found by finding the minimum of the average bit error rate curves.