Showing papers in "Annual Review of Biophysics and Biomolecular Structure in 2005"
TL;DR: The high-speed single-molecule tracking methods are described, and a new model of a partitioned fluid plasma membrane and the involvement of the actin-based membrane-skeleton "fences" and anchored-transmembrane protein "pickets" in the formation of compartment boundaries are critically reviewed.
Abstract: Recent advancements in single-molecule tracking methods with nanometer-level precision now allow researchers to observe the movement, recruitment, and activation of single molecules in the plasma membrane in living cells. In particular, on the basis of the observations by high-speed single-particle tracking at a frame rate of 40,000 frames s(1), the partitioning of the fluid plasma membrane into submicron compartments throughout the cell membrane and the hop diffusion of virtually all the molecules have been proposed. This could explain why the diffusion coefficients in the plasma membrane are considerably smaller than those in artificial membranes, and why the diffusion coefficient is reduced upon molecular complex formation (oligomerization-induced trapping). In this review, we first describe the high-speed single-molecule tracking methods, and then we critically review a new model of a partitioned fluid plasma membrane and the involvement of the actin-based membrane-skeleton "fences" and anchored-transmembrane protein "pickets" in the formation of compartment boundaries.
1,086 citations
TL;DR: This review summarizes the recent progress in the understanding of how the kinetics and energetics of membrane-protein interactions are regulated during the cellular membrane targeting and activation of peripheral proteins.
Abstract: ▪ Abstract Research in the past decade has revealed that many cytosolic proteins are recruited to different cellular membranes to form protein-protein and lipid-protein interactions during cell signaling and membrane trafficking. Membrane recruitment of these peripheral proteins is mediated by a growing number of modular membrane-targeting domains, including C1, C2, PH, FYVE, PX, ENTH, ANTH, BAR, FERM, and tubby domains, that recognize specific lipid molecules in the membranes. Structural studies of these membrane-targeting domains demonstrate how they specifically recognize their cognate lipid ligands. However, the mechanisms by which these domains and their host proteins are recruited to and interact with various cell membranes are only beginning to unravel with recent computational studies, in vitro membrane binding studies using model membranes, and cellular translocation studies using fluorescent protein-tagged proteins. This review summarizes the recent progress in our understanding of how the kinet...
593 citations
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TL;DR: This review distinguishes three different kinds of ion environments that differ in the extent of direct ion-RNA contacts and the degree to which the ion hydration is perturbed, and summarizes the current understanding of the way each environment relates to the overall energetics of RNA folding.
Abstract: The problem of how ions influence the folding of RNA into specific tertiary structures is being addressed from both thermodynamic (by how much do different salts affect the free energy change of folding) and structural (how are ions arranged on or near an RNA and what kinds of environments do they occupy) points of view. The challenge is to link these different approaches in a theoretical framework that relates the energetics of ion-RNA interactions to the spatial distribution of ions. This review distinguishes three different kinds of ion environments that differ in the extent of direct ion-RNA contacts and the degree to which the ion hydration is perturbed, and summarizes the current understanding of the way each environment relates to the overall energetics of RNA folding.
436 citations
TL;DR: A perspective from simple models on how the physical properties of water-as a pure liquid and as a solvent-derive from the geometric and hydrogen bonding properties ofwater is given.
Abstract: Water plays a central role in the structures and properties of biomolecules--proteins, nucleic acids, and membranes--and in their interactions with ligands and drugs. Over the past half century, our understanding of water has been advanced significantly owing to theoretical and computational modeling. However, like the blind men and the elephant, different models describe different aspects of water's behavior. The trend in water modeling has been toward finer-scale properties and increasing structural detail, at increasing computational expense. Recently, our labs and others have moved in the opposite direction, toward simpler physical models, focusing on more global properties-water's thermodynamics, phase diagram, and solvation properties, for example-and toward less computational expense. Simplified models can guide a better understanding of water in ways that complement what we learn from more complex models. One ultimate goal is more tractable models for computer simulations of biomolecules. This review gives a perspective from simple models on how the physical properties of water-as a pure liquid and as a solvent-derive from the geometric and hydrogen bonding properties of water.
381 citations
TL;DR: This review describes structural aspects of methylation of histone lysine residues by two enzyme families with entirely different structural scaffolding (the SET proteins and Dot1p) andmethylation of protein arginine residue by PRMTs.
Abstract: With genome sequencing nearing completion for the model organisms used in biomedical research, there is a rapidly growing appreciation that proteomics, the study of covalent modification to proteins, and transcriptional regulation will likely dominate the research headlines in the next decade. Protein methylation plays a central role in both of these fields, as several different residues (Arg, Lys, Gln) are methylated in cells and methylation plays a central role in the "histone code" that regulates chromatin structure and impacts transcription. In some cases, a single lysine can be mono-, di-, or trimethylated, with different functional consequences for each of the three forms. This review describes structural aspects of methylation of histone lysine residues by two enzyme families with entirely different structural scaffolding (the SET proteins and Dot1p) and methylation of protein arginine residues by PRMTs.
341 citations
TL;DR: The chemical synthesis of proteins is providing previously unattainable insight into the structure and function of proteins, enabling a level of control on protein composition that greatly exceeds that attainable with ribosome-mediated biosynthesis.
Abstract: Proteins have become accessible targets for chemical synthesis. The basic strategy is to use native chemical ligation, Staudinger ligation, or other orthogonal chemical reactions to couple synthetic peptides. The ligation reactions are compatible with a variety of solvents and proceed in solution or on a solid support. Chemical synthesis enables a level of control on protein composition that greatly exceeds that attainable with ribosome-mediated biosynthesis. Accordingly, the chemical synthesis of proteins is providing previously unattainable insight into the structure and function of proteins.
306 citations
TL;DR: Whether simulations have indeed rendered quantitative predictions in several areas, including protein folding kinetics, thermodynamics, and physics-based methods for structure prediction, is asked.
Abstract: Simulation of protein folding has come a long way in five years. Notably, new quantitative comparisons with experiments for small, rapidly folding proteins have become possible. As the only way to validate simulation methodology, this achievement marks a significant advance. Here, we detail these recent achievements and ask whether simulations have indeed rendered quantitative predictions in several areas, including protein folding kinetics, thermodynamics, and physics-based methods for structure prediction. We conclude by looking to the future of such comparisons between simulations and experiments.
246 citations
TL;DR: In this paper, a review of DNA toroid structure and the mechanism of their formation is presented, showing that the DNA strands within toroids can be packed in an ideal hexagonal lattice, and also in regions with a nonhexagonal topological constraint associated with winding DNA into a toroid.
Abstract: Toroidal DNA condensates have attracted the attention of biophysicists, biochemists, and polymer physicists for more than thirty years. In the biological community, the quest to understand DNA toroid formation has been motivated by its relevance to gene packing in certain viruses and by the potential use of DNA toroids in artificial gene delivery (e.g., gene therapy). In the physical sciences, DNA toroids are appreciated as a superb model system for studying particle formation by the collapse of a semiflexible, polyelectrolyte polymer. This review focuses on experimental studies from the past few years that have significantly increased our understanding of DNA toroid structure and the mechanism of their formation. Highlights include structural studies that show the DNA strands within toroids to be packed in an ideal hexagonal lattice, and also in regions with a nonhexagonal lattice that are required by the topological constraints associated with winding DNA into a toroid. Recent studies of DNA toroid formation have also revealed that toroid size limits result from a complex interplay between kinetic and thermodynamic factors that govern both toroid nucleation and growth. The work discussed in this review indicates that it will ultimately be possible to obtain substantial control over DNA toroid dimensions.
184 citations
TL;DR: It is shown how the patterns of interaction, either observed in known structures or derived from computer simulations, confer recognition specificity, and how they can be used to examine the relationship between structure and specificity and to predict target DNA sequences used by regulatory proteins.
Abstract: Structural data on protein-DNA complexes provide clues for understanding the mechanism of protein-DNA recognition. Although the structures of a large number of protein-DNA complexes are known, the mechanisms underlying their specific binding are still only poorly understood. Analysis of these structures has shown that there is no simple one-to-one correspondence between bases and amino acids within protein-DNA complexes; nevertheless, the observed patterns of interaction carry important information on the mechanisms of protein-DNA recognition. In this review, we show how the patterns of interaction, either observed in known structures or derived from computer simulations, confer recognition specificity, and how they can be used to examine the relationship between structure and specificity and to predict target DNA sequences used by regulatory proteins.
179 citations
TL;DR: The purpose of this review is to summarize the most important findings from experiments and computations and to highlight a number of fundamental mechanistic questions about ion conduction and selectivity that will require further work.
Abstract: ▪ Abstract Potassium (K+) channels are tetrameric membrane-spanning proteins that provide a selective pore for the conductance of K+ across the cell membranes. These channels are most remarkable in their ability to discriminate K+ from Na+ by more than a thousandfold and conduct at a throughput rate near diffusion limit. The recent progress in the structural characterization of K+ channel provides us with a unique opportunity to understand their function at the atomic level. With their ability to go beyond static structures, molecular dynamics simulations based on atomic models can play an important role in shaping our view of how ion channels carry out their function. The purpose of this review is to summarize the most important findings from experiments and computations and to highlight a number of fundamental mechanistic questions about ion conduction and selectivity that will require further work.
175 citations
TL;DR: This work states that recent single-molecule experiments on RNA folding and catalysis have improved the understanding of the folding energy landscape of RNA and allowed us to better dissect complex RNA catalytic reactions, including translation by the ribosome.
Abstract: The development of single-molecule detection and manipulation has allowed us to monitor the behavior of individual biological molecules and molecular complexes in real time. This approach significantly expands our capability to characterize complex dynamics of biological processes, allowing transient intermediate states and parallel kinetic pathways to be directly observed. Exploring this capability to elucidate complex dynamics, recent single-molecule experiments on RNA folding and catalysis have improved our understanding of the folding energy landscape of RNA and allowed us to better dissect complex RNA catalytic reactions, including translation by the ribosome.
TL;DR: This work has evaluated and distilled the large body of biochemical data into a consensus set of functional groups unambiguously required for hammerhead catalysis, and established a concise set of disagreements between the structural and functional data.
Abstract: A powerful approach to understanding protein enzyme catalysis is to examine the structural context of essential amino acid side chains whose deletion or modification negatively impacts catalysis. In principle, this approach can be even more powerful for RNA enzymes, given the wide variety and subtlety of functionally modified nucleotides now available. Numerous recent success stories confirm the utility of this approach to understanding ribozyme function. An anomaly, however, is the hammerhead ribozyme, for which the structural and functional data do not agree well, preventing a unifying view of its catalytic mechanism from emerging. To delineate the hammerhead structure-function comparison, we have evaluated and distilled the large body of biochemical data into a consensus set of functional groups unambiguously required for hammerhead catalysis. By examining the context of these functional groups within available structures, we have established a concise set of disagreements between the structural and functional data. The number and relative distribution of these inconsistencies throughout the hammerhead reaffirms that an extensive conformational rearrangement from the fold observed in the crystal structure must be necessary for cleavage to occur. The nature and energetic driving force of this conformational isomerization are discussed.
TL;DR: Single-molecule assays provide a unique way to study the uncoiling of single supercoiled DNA molecules and the unlinking of two intertwined DNAs, and shed new light on the mechanism of these enzymes and their function in vivo.
Abstract: The recent development of new techniques to manipulate single DNA molecules has opened new opportunities for the study of the enzymes that control DNA topology: the type I and II topoisomerases. These single-molecule assays provide a unique way to study the uncoiling of single supercoiled DNA molecules and the unlinking of two intertwined DNAs. They allow for a detailed characterization of the activity of topoisomerases, including the processivity, the chiral discrimination, and the dependence of their enzymatic rate on ATP concentration, degree of supercoiling, and the tension in the molecule. These results shed new light on the mechanism of these enzymes and their function in vivo.
TL;DR: The use of deterministic, stochastic, and hybrid models to represent cellular processes is reviewed, and an initial integrated approach for the development of large-scale predictive models of a mammalian cell is presented.
Abstract: Progress in experimental and theoretical biology is likely to provide us with the opportunity to assemble detailed predictive models of mammalian cells. Using a functional format to describe the organization of mammalian cells, we describe current approaches for developing qualitative and quantitative models using data from a variety of experimental sources. Recent developments and applications of graph theory to biological networks are reviewed. The use of these qualitative models to identify the topology of regulatory motifs and functional modules is discussed. Cellular homeostasis and plasticity are interpreted within the framework of balance between regulatory motifs and interactions between modules. From this analysis we identify the need for detailed quantitative models on the basis of the representation of the chemistry underlying the cellular process. The use of deterministic, stochastic, and hybrid models to represent cellular processes is reviewed, and an initial integrated approach for the development of large-scale predictive models of a mammalian cell is presented.
TL;DR: Novel methods for the determination of the bound ligand conformation, in particular transferred cross-correlated relaxation, are thoroughly reviewed, and their advantages with respect to established methodology are discussed, using the epothilone-tubulin complex as a primary example.
Abstract: ▪ Abstract The conformation of the ligand in complex with a macromolecular target can be studied by nuclear magnetic resonance (NMR) in solution for both tightly and weakly forming complexes. In the weak binding regime (koff > 104 Hz), the structure of the bound ligand is accessible also for very large complexes (>100 kDa), which are not amenable to NMR studies in the tight binding regime. Here I review the state-of-the-art NMR methodology used for screening ligands and for the structural investigation of bound ligand conformations, in both tight and weak binding regimes. The advantages and disadvantages of each approach are critically described. The NMR methodology used to investigate transiently forming complexes has expanded considerably in the past few years, opening new possibilities for a detailed description of ligand-target interactions. Novel methods for the determination of the bound ligand conformation, in particular transferred cross-correlated relaxation, are thoroughly reviewed, and their ad...
TL;DR: In this paper, an electron paramagnetic resonance (EPR) power saturation approach was used to determine the key geometric parameters of membrane-docked proteins, including their penetration depths and angular orientations relative to the membrane surface.
Abstract: ▪ Abstract Despite the central importance of peripheral membrane proteins to cellular signaling and metabolic pathways, the structures of protein-membrane interfaces remain largely inaccessible to high-resolution structural methods. In recent years a number of laboratories have contributed to the development of an electron paramagnetic resonance (EPR) power saturation approach that utilizes site-directed spin labeling to determine the key geometric parameters of membrane-docked proteins, including their penetration depths and angular orientations relative to the membrane surface. Representative applications to Ca2+-activated, membrane-docking C2 domains are described.
TL;DR: It is proposed that through-solution dialogue is a general property of all biopolymers and should be considered when assessing reactions of multicomponent systems such as those that exist in essentially all biological processes.
Abstract: Molecular interactions are the language that molecules use to communicate recognition, binding, and regulation, events central to biological control mechanisms. Traditionally, such interactions involve direct, atom-to-atom, noncovalent contacts, or indirect contacts bridged by relatively fixed solvent molecules. Here we discuss a third class of molecular communication that, to date, has received less experimental attention, namely solvent-mediated communication between noncontacting macromolecules. This form of communication can be understood in terms of fundamental, well-established principles (coupled equilibria and linkage thermodynamics) that govern interactions between individual polymers and their solutions. In contrast to simple solutions used in laboratory studies, biological systems contain a multitude of nominally noninteracting biopolymers within the same solution environment. The exquisite control of biological function requires some form of communication between many of these solution components, even in the absence of direct and/or indirect contacts. Such communication must be considered when describing potential mechanisms of biological regulation.