Fast empirical pKa prediction by Ewald summation

Item does not contain fulltextpK(a) calculations for macromolecules are normally performed by solving the Poisson-Boltzmann equation, accounting for the different dielectric constants of solvent and solute, as well as the ionic strength. Despite the large number of successful applications, there are some situations where the current algorithms are not suitable: (1) large scale, high-throughput analysis which requires calculations to be completed within a fraction of a second, e.g. when permanently monitoring pK(a) shifts during a molecular dynamics simulation; (2) prediction of pK(a)s in periodic boundaries, e.g. when reconstructing entire protein crystal unit cells from PDB files, including the correct protonation patterns at experimental pH. Such in silico crystals are needed by 'self-parameterizing' molecular dynamics force fields like YASARA YAMBER, that optimize their parameters while energy-minimizing high-resolution protein crystals. To address both problems, we define an empirical equation that expresses the pK(a) as a function of electrostatic potential, hydrogen bonds and accessible surface area. The electrostatic potential is evaluated by Ewald summation, which captures periodic crystal environments and the uncertainty in atom positions using Gaussian charge densities. The empirical proportionality constants are derived from 217 experimentally determined pK(a)s, and despite its simplicity, this pK(a) calculation method reaches a high overall jack-knifed accuracy, and is fast enough to be used during a molecular dynamics simulation. A reliable null-model to judge pK(a) prediction accuracies is also presented

Validation of High-Resolution NMR-Structures

Contains fulltext : 59140.pdf (publisher's version ) (Closed access

Refinement of protein structures in explicit solvent

We present a CPU efficient protocol for refinement of protein structures in a thin layer of explicit solvent and energy parameters with completely revised dihedral angle terms. Our approach is suitable for protein structures determined by theoretical (e.g., homology modeling or threading) or experimental methods (e.g., NMR). In contrast to other recently proposed refinement protocols, we put a strong emphasis on consistency with widely accepted covalent parameters and computational efficiency. We illustrate the method for NMR structure calculations of three proteins: interleukin- 4, ubiquitin, and crambin. We show a comparison of their structure ensembles before and after refinement in water with and without a force field energy term for the dihedral angles; crambin was also refined in DMSO. Our results demonstrate the significant improvement of structure quality by a short refinement in a thin layer of solvent. Further, they show that a dihedral angle energy term in the force field is beneficial for structure calculation and refinement. We discuss the optimal weight for the energy constant for the backbone angle omega and include an extensive discussion of meaning and relevance of the calculated validation criteria, in particular root mean square Z scores for covalent parameters such as bond lengths. Proteins 2003;50: 496–506

Postburn contracture treatment: a healthcare project in Bangladesh.

Contains fulltext : 71448.pdf (publisher's version ) (Closed access)Over the last 6 years, a health care program aimed at the surgical correction of postburn contractures has taken place in Faridpur, Bangladesh. People in this rural region are very poor and often cannot afford medical treatment. Often secondary flexion contractures of the face and chin as well as the upper and lower extremity impede daily functioning and have an enormous psycho-social impact. The application of basic plastic surgical principles such as local transposition of skin flaps as well as skin grafts restores function dramatically and results in stable skin cover. It is quite challenging - both for the surgeon and the anaesthesiologist - to perform these operations within a rather limited infrastructure. In Bangladesh, there is a monumental need for correction of postburn contractures for the social needs of the patient as well as for functional purposes. Future actions should be directed to the training of surgeons and the development of specialized hospitals to demonstrate social as well as political commitment to health care programs

The precision of NMR structure ensembles revisited.

Contains fulltext : 79477.pdf (publisher's version ) (Closed access)Biomolecular structures provide the basis for many studies in research areas such as structure-based drug design and homology modeling. In order to use molecular coordinates it is important that they are reliable in terms of accurate description of the experimental data and in terms of the overall and local geometry. Besides these primary quality criteria an indication is needed for the uncertainty in the atomic coordinates that may arise from the dynamic behavior of the considered molecules as well as from experimental- and computational procedures.In contrast to the crystallographic B-factor, a good measure for the uncertainty in NMR-derived atomic coordinates is still not available. It has become clear in recent years that the widely used atomic Root Mean Square Deviation (RMSD), which is a measure for the precision of the data, overestimates the accuracy of NMR structure ensembles and therefore is a problematic measure for the uncertainty in the atomic coordinates.In this study we report a method that yields a more realistic estimate of the uncertainty in the atomic coordinates by maximizing the RMSD of an ensemble of structures, while maintaining the accordance with the experimentally derived data. The results indicate that the RMSD of most NMR structure ensembles can be significantly increased compromising neither geometric quality nor NMR data. This maximized RMSD therefore seems a better estimate of the true uncertainty in the atomic coordinates

Surface location and orientation of the lantibiotic nisin bound to membrane-mimicking micelles of dodecylphosphocholine and of sodium dodecylsulphate

Contains fulltext : 28467.pdf (publisher's version ) (Open Access

Extension of the binding motif of the Sin3 interacting domain of the Mad family proteins.

Contains fulltext : 58506.pdf (publisher's version ) (Closed access)Sin3 forms the scaffold for a multiprotein corepressor complex that silences transcription via the action of histone deacetylases. Sin3 is recruited to the DNA by several DNA binding repressors, such as the helix-loop-helix proteins of the Mad family. Here, we elaborate on the Mad-Sin3 interaction based on a binding study, solution structure, and dynamics of the PAH2 domain of mSin3 in complex to an extended Sin3 interacting domain (SID) of 24 residues of Mad1. We show that SID residues Met7 and Glu23, outside the previously defined minimal binding motif, mediate additional hydrophobic and electrostatic interactions with PAH2. On the basis of these results we propose an extended consensus sequence describing the PAH2-SID interaction specifically for the Mad family, showing that residues outside the hydrophobic core of the SID interact with PAH2 and modulate binding affinity to appropriate levels

Structure, dynamics and binding characteristics of the second PDZ domain of PTP-BL.

Contains fulltext : 187660.pdf (publisher's version ) (Closed access)The PDZ domains of the protein tyrosine phosphatase PTP-BL mediate interactions by binding to specific amino acid sequences in target proteins. The solution structure of the second PDZ domain of PTP-BL, PDZ2, displays a compact fold with six beta strands and two alpha-helices. A unique feature of this domain compared to the canonical PDZ fold is an extended flexible loop at the base of the binding pocket, termed L1, that folds back onto the protein backbone, a feature that is shared by both the murine and human orthologues. The structure of PDZ2 differs significantly from the orthologous human structure. A comparison of structural quality indicators clearly demonstrates that the PDZ2 ensemble is statistically more reasonable than that of the human orthologue. The analysis of (15)N relaxation data for PDZ2 shows a normal pattern, with more rigid secondary structures and more flexible loop structures. Close to the binding pocket, Leu85 and Thr88 display greater mobility when compared to surrounding residues. Peptide binding studies demonstrated a lack of interaction between murine PDZ2 and the C terminus of the murine Fas/CD95 receptor, suggesting that the Fas/CD95 receptor is not an in vivo target for PDZ2. In addition, PDZ2 specifically binds the C termini of both human Fas/CD95 receptor and the RIL protein, despite RIL containing a non-canonical PDZ-interacting sequence of E-x-V. A model of PDZ2 with the RIL peptide reveals that the PDZ2 binding pocket is able to accommodate the bulkier side-chain of glutamic acid while maintaining crucial protein to peptide hydrogen bond interactions

The Mad1-Sin3B interaction involves a novel helical fold.

Contains fulltext : 79474.pdf (publisher's version ) (Closed access)Sin3A or Sin3B are components of a corepressor complex that mediates repression by transcription factors such as the helix-loop-helix proteins Mad and Mxi. Members of the Mad/Mxi family of repressors play important roles in the transition between proliferation and differentiation by down-regulating the expression of genes that are activated by the proto-oncogene product Myc. Here, we report the solution structure of the second paired amphipathic helix (PAH) domain (PAH2) of Sin3B in complex with a peptide comprising the N-terminal region of Mad1. This complex exhibits a novel interaction fold for which we propose the name 'wedged helical bundle'. Four alpha-helices of PAH2 form a hydrophobic cleft that accommodates an amphipathic Mad1 alpha-helix. Our data further show that, upon binding Mad1, secondary structure elements of PAH2 are stabilized. The PAH2-Mad1 structure provides the basis for determining the principles of protein interaction and selectivity involving PAH domains

DRESS: a database of refined solution NMR structures

Several studies have shown that biomolecular NMR structures are often of lower quality when compared to crystal structures, and consequently they are often excluded from structural analyses. We present a publicly available database of re-refinedNMRstructures, exhibiting significantly improved quality. This database (available at http://www.cmbi.kun.nl/dress/) presents a uniformly refined and validated set of structural models that improves the value of theseNMRstructures as input for experimental and theoretical studies in many fields of research. Proteins 2004;55:483–486