83,194 research outputs found
Maximum Flux Transition Paths of Conformational Change
Given two metastable states A and B of a biomolecular system, the problem is
to calculate the likely paths of the transition from A to B. Such a calculation
is more informative and more manageable if done for a reduced set of collective
variables chosen so that paths cluster in collective variable space. The
computational task becomes that of computing the "center" of such a cluster. A
good way to define the center employs the concept of a committor, whose value
at a point in collective variable space is the probability that a trajectory at
that point will reach B before A. The committor "foliates" the transition
region into a set of isocommittors. The maximum flux transition path is defined
as a path that crosses each isocommittor at a point which (locally) has the
highest crossing rate of distinct reactive trajectories. (This path is
different from that of the MaxFlux method of Huo and Straub.) It is argued that
such a path is nearer to an ideal path than others that have been proposed with
the possible exception of the finite-temperature string method path. To make
the calculation tractable, three approximations are introduced, yielding a path
that is the solution of a nonsingular two-point boundary-value problem. For
such a problem, one can construct a simple and robust algorithm. One such
algorithm and its performance is discussed.Comment: 7 figure
Charge environments around phosphorylation sites in proteins
Background: Phosphorylation is a central feature in many biological processes. Structural analyses
have identified the importance of charge-charge interactions, for example mediating
phosphorylation-driven allosteric change and protein binding to phosphopeptides. Here, we
examine computationally the prevalence of charge stabilisation around phosphorylated sites in the
structural database, through comparison with locations that are not phosphorylated in the same
structures.
Results: A significant fraction of phosphorylated sites appear to be electrostatically stabilised,
largely through interaction with sidechains. Some examples of stabilisation across a subunit
interface are evident from calculations with biological units. When considering the immediately
surrounding environment, in many cases favourable interactions are only apparent after
conformational change that accompanies phosphorylation. A simple calculation of potential
interactions at longer-range, applied to non-phosphorylated structures, recovers the separation
exhibited by phosphorylated structures. In a study of sites in the Phospho.ELM dataset, for which
structural annotation is provided by non-phosphorylated proteins, there is little separation of the
known phospho-acceptor sites relative to background, even using the wider interaction radius.
However, there are differences in the distributions of patch polarity for acceptor and background
sites in the Phospho.ELM dataset.
Conclusion: In this study, an easy to implement procedure is developed that could contribute to
the identification of phospho-acceptor sites associated with charge-charge interactions and
conformational change. Since the method gives information about potential anchoring interactions
subsequent to phosphorylation, it could be combined with simulations that probe conformational
change. Our analysis of the Phospho.ELM dataset also shows evidence for mediation of
phosphorylation effects through (i) conformational change associated with making a solvent
inaccessible phospho-acceptor site accessible, and (ii) modulation of protein-protein interactions
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Anion transport inhibitor binding to band 3 in red blood cell membranes.
The inhibitor of anion exchange 4,4'-dibenzoamido-2,2'-disulfonic stilbene (DBDS) binds to band 3, the anion transport protein in human red cell ghost membranes, and undergoes a large increase in fluorescence intensity when bound to band 3. Equilibrium binding studies performed in the absence of transportable anions show that DBDS binds to both a class of high-affinity (65 nM) and low-affinity (820 nM) sites with stoichiometry equivalent to 1.6 nmol/mg ghost protein for each site, which is consistent with one DBDS site on each band 3 monomer. The kinetics of DBDS binding were studied both by stopped-flow and temperature-jump experiments. The stopped-flow data indicate that DBDS binding to the apparent high-affinity site involves association with a low-affinity site (3 microM) followed by a slow (4 s-1) conformational change that locks the DBDS molecule in place. A detailed, quantitative fit of the temperature-jump data to several binding mechanisms supports a sequential-binding model, in which a first DBDS molecule binds to one monomer and induces a conformational change. A second DBDS molecule then binds to the second monomer. If the two monomers are assumed to be initially identical, thermodynamic characterization of the binding sites shows that the conformational change induces an interaction between the two monomers that modifies the characteristics of the second DBDS binding site
Molecular recognition mechanisms of calmodulin examined by perturbation-response scanning
We analyze the apo and holo calmodulin (CaM) structures by sequentially inserting a perturbation on every residue of the protein, and monitoring the linear response. Residue crosscorrelation matrices obtained from 20 ns long molecular dynamics simulation of the apo-form are used as the kernel in the linear response. We determine two residues whose perturbation equivalently yields the experimentally determined displacement profiles of CaM, relevant to the binding of the trifluoperazine (TFP) ligand. They reside on structurally equivalent positions on the N- and C-terminus lobes of CaM, and are not in direct contact with the binding region. The direction of the perturbation that must be inserted on these residues is an important factor in recovering the conformational change, implying that highly selective binding must occur near
these sites to invoke the necessary conformational change
A network model to investigate structural and electrical properties of proteins
One of the main trend in to date research and development is the
miniaturization of electronic devices. In this perspective, integrated
nanodevices based on proteins or biomolecules are attracting a major interest.
In fact, it has been shown that proteins like bacteriorhodopsin and azurin,
manifest electrical properties which are promising for the development of
active components in the field of molecular electronics. Here we focus on two
relevant kinds of proteins: The bovine rhodopsin, prototype of GPCR protein,
and the enzyme acetylcholinesterase (AChE), whose inhibition is one of the most
qualified treatments of Alzheimer disease. Both these proteins exert their
functioning starting with a conformational change of their native structure.
Our guess is that such a change should be accompanied with a detectable
variation of their electrical properties. To investigate this conjecture, we
present an impedance network model of proteins, able to estimate the different
electrical response associated with the different configurations. The model
resolution of the electrical response is found able to monitor the structure
and the conformational change of the given protein. In this respect, rhodopsin
exhibits a better differential response than AChE. This result gives room to
different interpretations of the degree of conformational change and in
particular supports a recent hypothesis on the existence of a mixed state
already in the native configuration of the protein.Comment: 25 pages, 12 figure
Structure of protease-cleaved escherichia coliα-2-macroglobulin reveals a putative mechanism of conformational activation for protease entrapment
Bacterial -2-macroglobulins have been suggested to function in defence as broad-spectrum inhibitors of host proteases that breach the outer membrane. Here, the X-ray structure of protease-cleaved Escherichia coli -2-macroglobulin is described, which reveals a putative mechanism of activation and conformational change essential for protease inhibition. In this competitive mechanism, protease cleavage of the bait-region domain results in the untethering of an intrinsically disordered region of this domain which disrupts native interdomain interactions that maintain E. coli -2-macroglobulin in the inactivated form. The resulting global conformational change results in entrapment of the protease and activation of the thioester bond that covalently links to the attacking protease. Owing to the similarity in structure and domain architecture of Escherichia coli -2-macroglobulin and human -2-macroglobulin, this protease-activation mechanism is likely to operate across the diverse members of this group
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