1,721,075 research outputs found
Reply to "comment on A Tensor-Free Method for the Structural and Dynamic Refinement of Proteins using Residual Dipolar Couplings"
No full textStatistical mechanics of the denatured state of a protein using replica-averaged metadynamics
No full textThe characterization of denatured states of proteins is challenging because the lack of permanent structure in these states makes it difficult to apply to them standard methods of structural biology. In this work we use all-atom replica-averaged metadynamics (RAM) simulations with NMR chemical shift restraints to determine an ensemble of structures representing an acid-denatured state of the 86-residue protein ACBP. This approach has enabled us to reach convergence in the free energy landscape calculations, obtaining an ensemble of structures in relatively accurate agreement with independent experimental data used for validation. By observing at atomistic resolution the transient formation of native and non-native structures in this acid-denatured state of ACBP, we rationalize the effects of single-point mutations on the folding rate, stability, and transition-state structures of this protein, thus characterizing the role of the unfolded state in determining the folding process
Assessment of the use of NMR chemical shifts as replica-averaged structural restraints in molecular dynamics simulations to characterize the dynamics of proteins
No full textIt has been recently proposed that NMR chemical shifts can be used as replica-averaged structural restraints in molecular dynamics simulations to determine the conformational fluctuations of proteins. In this work, we assess the accuracy of this approach by considering its application to the case of ribonuclease A. We found that the agreement between experimental and calculated chemical shifts improves on average when the chemical shifts are used as replica-averaged restraints with respect to the cases in which X-ray structures or ensembles of structures obtained by standard molecular dynamics simulations are considered. These results indicate that the use of chemical shifts as structural restraints enables a bias of the conformational sampling to be introduced in a system-specific manner to reproduce accurately the conformational fluctuations of proteins
A relationship between the aggregation rates of α-synuclein variants and the β-sheet populations in their monomeric forms
No full textIntrinsically disordered proteins constitute a significant part of the human proteome and carry out a wide range of different functions, including in particular signaling and regulation. Several of these proteins are vulnerable to aggregation, and their aberrant assemblies have been associated with a variety of neurodegenerative and systemic diseases. It remains unclear, however, the extent to which the conformational properties of intrinsically disordered proteins in their monomeric states influence the aggregation behavior of these molecules. Here we report a relationship between aggregation rates and secondary structure populations in the soluble monomeric states of a series of mutational variants of α-synuclein. Overall, we found a correlation of over 90% between the changes in β-sheet populations calculated from NMR chemical shift data and the changes in aggregation rates for eight human-to-mouse chimeric mutants. These results provide support to the idea of investigating therapeutic strategies based on the stabilization of the monomeric form of intrinsically disordered proteins through the alteration of their conformational properties
A tensor-free method for the structural and dynamical refinement of proteins using residual dipolar couplings
No full textResidual dipolar couplings (RDCs) are parameters measured in nuclear magnetic resonance spectroscopy that can provide exquisitely detailed information about the structure and dynamics of biological macromolecules. We describe here a method of using RDCs for the structural and dynamical refinement of proteins that is based on the observation that the RDC between two atomic nuclei depends directly on the angle ∂ between the internuclear vector and the external magnetic field. For every pair of nuclei for which an RDC is available experimentally, we introduce a structural restraint to minimize the deviation from the value of the angle ∂ derived from the measured RDC and that calculated in the refinement protocol. As each restraint involves only the calculation of the angle ∂ of the corresponding internuclear vector, the method does not require the definition of an overall alignment tensor to describe the preferred orientation of the protein with respect to the alignment medium. Application to the case of ubiquitin demonstrates that this method enables an accurate refinement of the structure and dynamics of this protein to be obtained
Determination of the conformational states of strychnine in solution using NMR residual dipolar couplings in a tensor-free approach
No full textSmall molecules with rotatable bonds can occupy different conformational states in solution as a consequence of their thermal fluctuations. The accurate determination of the structures of such states, as well as of their statistical weights, has been challenging because of the technical difficulties in extracting information from experimental measurements, which are normally averaged over the conformational space available. Here, to achieve this objective, we present an approach based on a recently proposed tensor-free method for incorporating NMR residual dipolar couplings as structural restraints in replica-averaged molecular dynamics simulations. This approach enables the information provided by the experimental data to be used in the spirit of the maximum entropy principle to determine the structural ensembles of small molecules. Furthermore, in order to enhance the sampling of the conformational space we incorporated the metadynamics method in the simulations. We illustrate the method in the case of strychnine, determining the three major conformational states of this small molecule and their associated occupation probabilities
Determination of secondary structure populations in disordered states of proteins using nuclear magnetic resonance chemical shifts
No full textOne of the major open challenges in structural biology is to achieve effective descriptions of disordered states of proteins. This problem is difficult because these states are conformationally highly heterogeneous and cannot be represented as single structures, and therefore it is necessary to characterize their conformational properties in terms of probability distributions. Here we show that it is possible to obtain highly quantitative information about particularly important types of probability distributions, the populations of secondary structure elements (α-helix, β-strand, random coil, and polyproline II), by using the information provided by backbone chemical shifts. The application of this approach to mammalian prions indicates that for these proteins a key role in molecular recognition is played by disordered regions characterized by highly conserved polyproline II populations. We also determine the secondary structure populations of a range of other disordered proteins that are medically relevant, including p53, α-synuclein, and the Aβ peptide, as well as an oligomeric form of αB-crystallin. Because chemical shifts are the nuclear magnetic resonance parameters that can be measured under the widest variety of conditions, our approach can be used to obtain detailed information about secondary structure populations for a vast range of different protein states
Optimal protein design procedure
No full textWe discuss a general method for protein design based on an analysis in sequence space of the Boltzmann weight for a given target structure. An efficient Monte Carlo code that explores sequence space (and, for each sequence, the space of compact and noncompact conformations) is implemented and tested in two models in two dimensions which are amenable to an exact solution-the design procedure is always successful
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
