An alpha helix is a sequence of amino acids in a protein that are twisted into a coil.
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and molecule is often used when referring to polyatomic ions.
Molecular dynamics (MD) is a computer simulation method for analyzing the physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamic "evolution" of the system. In the most common version, the trajectories of atoms and molecules are determined by numerically solving Newton's equations of motion for a system of interacting particles, where forces between the particles and their potential energies are often calculated using interatomic potentials or molecular mechanical force fields. The method is applied mostly in chemical physics, materials science, and biophysics.
GROningen MOlecular Simulation (GROMOS) is the name of a force field for molecular dynamics simulation, and a related computer software package. Both are developed at the University of Groningen, and at the Computer-Aided Chemistry Group at the Laboratory for Physical Chemistry at the Swiss Federal Institute of Technology (ETH Zurich). At Groningen, Herman Berendsen was involved in its development.
Molecular mechanics uses classical mechanics to model molecular systems. The Born–Oppenheimer approximation is assumed valid and the potential energy of all systems is calculated as a function of the nuclear coordinates using force fields. Molecular mechanics can be used to study molecule systems ranging in size and complexity from small to large biological systems or material assemblies with many thousands to millions of atoms.
A kinemage is an interactive graphic scientific illustration. It often is used to visualize molecules, especially proteins although it can also represent other types of 3-dimensional data. The kinemage system is designed to optimize ease of use, interactive performance, and the perception and communication of detailed 3D information. The kinemage information is stored in a text file, human- and machine-readable, that describes the hierarchy of display objects and their properties, and includes optional explanatory text. The kinemage format is a defined chemical MIME type of 'chemical/x-kinemage' with the file extension '.kin'.
Visual Molecular Dynamics (VMD) is a molecular modelling and visualization computer program. VMD is developed mainly as a tool to view and analyze the results of molecular dynamics simulations. It also includes tools for working with volumetric data, sequence data, and arbitrary graphics objects. Molecular scenes can be exported to external rendering tools such as POV-Ray, RenderMan, Tachyon, Virtual Reality Modeling Language (VRML), and many others. Users can run their own Tcl and Python scripts within VMD as it includes embedded Tcl and Python interpreters. VMD runs on Unix, Apple Mac macOS, and Microsoft Windows. VMD is available to non-commercial users under a distribution-specific license which permits both use of the program and modification of its source code, at no charge.
A chemical file format is a type of data file which is used specifically for depicting molecular data. One of the most widely used is the chemical table file format, which is similar to Structure Data Format (SDF) files. They are text files that represent multiple chemical structure records and associated data fields. The XYZ file format is a simple format that usually gives the number of atoms in the first line, a comment on the second, followed by a number of lines with atomic symbols and cartesian coordinates. The Protein Data Bank Format is commonly used for proteins but is also used for other types of molecules. There are many other types which are detailed below. Various software systems are available to convert from one format to another.
Nuclear magnetic resonance spectroscopy of proteins is a field of structural biology in which NMR spectroscopy is used to obtain information about the structure and dynamics of proteins, and also nucleic acids, and their complexes. The field was pioneered by Richard R. Ernst and Kurt Wüthrich at the ETH, and by Ad Bax, Marius Clore, Angela Gronenborn at the NIH, and Gerhard Wagner at Harvard University, among others. Structure determination by NMR spectroscopy usually consists of several phases, each using a separate set of highly specialized techniques. The sample is prepared, measurements are made, interpretive approaches are applied, and a structure is calculated and validated.
The Protein Data Bank (PDB) file format is a textual file format describing the three-dimensional structures of molecules held in the Protein Data Bank, now succeeded by the mmCIF format. The PDB format accordingly provides for description and annotation of protein and nucleic acid structures including atomic coordinates, secondary structure assignments, as well as atomic connectivity. In addition experimental metadata are stored. The PDB format is the legacy file format for the Protein Data Bank which has kept data on biological macromolecules in the newer PDBx/mmCIF file format since 2014.
Molecular graphics is the discipline and philosophy of studying molecules and their properties through graphical representation. IUPAC limits the definition to representations on a "graphical display device". Ever since Dalton's atoms and Kekulé's benzene, there has been a rich history of hand-drawn atoms and molecules, and these representations have had an important influence on modern molecular graphics.
Biomolecular structure is the intricate folded, three-dimensional shape that is formed by a molecule of protein, DNA, or RNA, and that is important to its function. The structure of these molecules may be considered at any of several length scales ranging from the level of individual atoms to the relationships among entire protein subunits. This useful distinction among scales is often expressed as a decomposition of molecular structure into four levels: primary, secondary, tertiary, and quaternary. The scaffold for this multiscale organization of the molecule arises at the secondary level, where the fundamental structural elements are the molecule's various hydrogen bonds. This leads to several recognizable domains of protein structure and nucleic acid structure, including such secondary-structure features as alpha helixes and beta sheets for proteins, and hairpin loops, bulges, and internal loops for nucleic acids. The terms primary, secondary, tertiary, and quaternary structure were introduced by Kaj Ulrik Linderstrøm-Lang in his 1951 Lane Medical Lectures at Stanford University.
Sirius is a molecular modelling and analysis system developed at San Diego Supercomputer Center. Sirius is designed to support advanced user requirements that go beyond simple display of small molecules and proteins. Sirius supports high quality interactive 3D graphics, structure building, displaying protein or DNA primary sequences, access to remote data sources, and visualizing molecular dynamics trajectories. It can be used for scientific visualization and analysis, and chemistry and biology instruction.
In the fields of chemical graph theory, molecular topology, and mathematical chemistry, a topological index, also known as a connectivity index, is a type of a molecular descriptor that is calculated based on the molecular graph of a chemical compound. Topological indices are numerical parameters of a graph which characterize its topology and are usually graph invariant. Topological indices are used for example in the development of quantitative structure-activity relationships (QSARs) in which the biological activity or other properties of molecules are correlated with their chemical structure.
The Asx turn is a structural feature in proteins and polypeptides. It consists of three amino acid residues in which residue i is an aspartate (Asp) or asparagine (Asn) that forms a hydrogen bond from its sidechain CO group to the mainchain NH group of residue i+2. About 14% of Asx residues present in proteins belong to Asx turns.
Volume, Area, Dihedral Angle Reporter (VADAR) is a freely available protein structure validation web server that was developed as a collaboration between Dr. Brian Sykes and Dr. David Wishart at the University of Alberta. VADAR consists of over 15 different algorithms and programs for assessing and validating peptide and protein structures from their PDB coordinate data. VADAR is capable of determining secondary structure, identifying and classifying six different types of beta turns, determining and calculating the strength of C=O -- N-H hydrogen bonds, calculating residue-specific accessible surface areas (ASA), calculating residue volumes, determining backbone and side chain torsion angles, assessing local structure quality, evaluating global structure quality, and identifying residue "outliers". The results have been validated through extensive comparison to published data and careful visual inspection. VADAR produces both text and graphical output with most of the quantitative data presented in easily viewed tables. In particular, VADAR's output is presented in a vertical, tabular format with most of the sequence data, residue numbering and any other calculated property or feature presented from top to bottom, rather than from left to right.
LiSiCA is a ligand-based virtual screening software that searches for 2D and 3D similarities between a reference compound and a database of target compounds which should be represented in a Mol2 format. The similarities are expressed using the Tanimoto coefficients and the target compounds are ranked accordingly. LiSiCA is also available as LiSiCA PyMOL plugin both on Linux and Windows operating systems.
MBN Explorer is a software package for molecular dynamics simulations, structure optimization and kinetic Monte Carlo simulations. It is designed for multiscale computational analysis of structure and dynamics of atomic clusters and nanoparticles, biomolecules and nanosystems, nanostructured materials, different states of matter and various interfaces. The software has been developed by MBN Research Center.
In biochemistry, a backbone-dependent rotamer library provides the frequencies, mean dihedral angles, and standard deviations of the discrete conformations of the amino acid side chains in proteins as a function of the backbone dihedral angles φ and ψ of the Ramachandran map. By contrast, backbone-independent rotamer libraries express the frequencies and mean dihedral angles for all side chains in proteins, regardless of the backbone conformation of each residue type. Backbone-dependent rotamer libraries have been shown to have significant advantages over backbone-independent rotamer libraries, principally when used as an energy term, by speeding up search times of side-chain packing algorithms used in protein structure prediction and protein design.
