12 research outputs found
Detailed Structure of the H<sub>2</sub>PO<sub>4</sub><sup>ā</sup>āGuanosine Diphosphate Intermediate in Ras-GAP Decoded from FTIR Experiments by Biomolecular Simulations
Essential biochemical processes such as signal transduction,
energy
conversion, or substrate conversion depend on transient ligand binding.
Thus, identifying the detailed structure and transient positioning
of small ligands, and their stabilization by the surrounding protein,
is of great importance. In this study, by decoding information from
Fourier transform infrared (FTIR) spectra with biomolecular simulation
methods, we identify the precise position and hydrogen network of
a small compound, the guanosine diphosphate (GDP)āH<sub>2</sub>PO<sub>4</sub><sup>ā</sup> intermediate, in the surrounding
proteināprotein complex of Ras and its GTPase-activating protein,
a central molecular switch in cellular signal transduction. We validate
the simulated structure by comparing the calculated fingerprint vibrational
modes of H<sub>2</sub>PO<sub>4</sub><sup>ā</sup> with those
obtained from FTIR experiments. The new structural information, below
the resolution of X-ray structural analysis, gives detailed insight
into the catalytic mechanism
Exploring the Multidimensional Free Energy Surface of Phosphoester Hydrolysis with Constrained QM/MM Dynamics
The mechanism of the hydrolysis of phosphate monoesters,
a ubiquitous
biological reaction, has remained under debate. We here investigated
the hydrolysis of a nonenzymatic model system, the monomethyl phosphate
dianion, by hybrid quantum mechanical and molecular mechanical simulations.
The solvation effects were taken into account with explicit water.
Detailed free energy landscapes in two-dimensional and three-dimensional
space were resolved using the multidimensional potential of mean constraint
force, a newly developed method that was demonstrated to be powerful
for free energy calculations along multiple coordinates. As in previous
theoretical studies, the associative and dissociative pathways were
indistinguishable. Furthermore, the associative pathway was investigated
in great detail. We propose a rotation of an OāH bond in the
transition between two pentacoordinated structures, during which an
overall transition state was identified with an activation energy
of 50 kcal/mol. This is consistent with experimental data. The results
support a concerted proton transfer from the nucleophilic water to
the phosphate group, and then to the leaving group
Reaction Mechanism of Adenylyltransferase DrrA from <i>Legionella pneumophila</i> Elucidated by Time-Resolved Fourier Transform Infrared Spectroscopy
Modulation
of the function of small GTPases that regulate vesicular
trafficking is a strategy employed by several human pathogens. <i>Legionella pneumophila</i> infects lung macrophages and injects
a plethora of different proteins into its host cell. Among these is
DrrA/SidM, which catalyzes stable adenylylation of Rab1b, a regulator
of endoplasmatic reticulum to Golgi trafficking, and thereby alters
the function and interactions of this small GTPase. We employed time-resolved
FTIR-spectroscopy to monitor the DrrA-catalyzed AMP-transfer to Tyr77
of Rab1b. A transient complex between DrrA, adenylylated Rab1b, and
the pyrophosphate byproduct was resolved, allowing us to analyze the
interactions at the active site. Combination of isotopic labeling
and site-directed mutagenesis allowed us to derive the catalytic mechanism
of DrrA from the FTIR difference spectra. DrrA shares crucial residues
in the ATP-binding pocket with similar AMP-transferring enzymes such
as glutamine synthetase adenylyltransferase or kanamycin nucleotidyltransferase,
but provides the complete active site on a single subunit. We determined
that Asp112 of DrrA functions as the catalytic base for deprotonation
of Tyr77 of Rab1b to enable nucleophilic attack on the ATP. The study
provides detailed understanding of the <i>Legionella pneumophila</i> protein DrrA and of AMP-transfer reactions in general
Universal Method for Protein Immobilization on Chemically Functionalized Germanium Investigated by ATR-FTIR Difference Spectroscopy
Attenuated total
reflection Fourier transform infrared (ATR-FTIR) spectroscopy allows
a detailed analysis of surface attached molecules, including their
secondary structure, orientation, and interaction with small molecules
in the case of proteins. Here, we present a universal immobilization
technique on germanium for all oligo-histidine-tagged proteins. For
this purpose, new triethoxysilane derivates were developed: we synthesized
a linkerāsilane with a succinimidyl ester as amine-reactive
headgroup and a matrixāsilane with an unreactive ethylene glycol
group. A new methodology for the attachment of triethoxysilanes on
germanium was established, and the surface was characterized by ATR-FTIR
and X-ray photoelectron spectroscopy. In the next step, the succinimidyl
ester was reacted with aminonitrilotriacetic acid. Subsequently, Ni<sup>2+</sup> was coordinated to form Niānitrilotriacetic acid
for His-tag binding. The capability of the functionalized surface
was demonstrated by experiments using the small GTPase Ras and photosystem
I (PS I). The native binding of the proteins was proven by difference
spectroscopy, which probes protein function. The function of Ras as
molecular switch was demonstrated by a beryllium trifluoride anion
titration assay, which allows observation of the āonā
and āoffā switching of Ras at atomic resolution. Furthermore,
the activity of immobilized PS I was proven by light-induced difference
spectroscopy. Subsequent treatment with imidazole removes attached
proteins, enabling repeated binding. This universal technique allows
specific attachment of His-tagged proteins and a detailed study of
their function at the atomic level using FTIR difference spectroscopy
An ATRāFTIR Sensor Unraveling the Drug Intervention of Methylene Blue, Congo Red, and Berberine on Human Tau and AĪ²
Alzheimerās
disease affects millions of human beings worldwide.
The disease progression is characterized by the formation of plaques
and neurofibrillary tangles in the brain, which are based on aggregation
processes of the AĪ² peptide and tau protein. Today there is
no cure and even no <i>in vitro</i> assay available for
the identification of drug candidates, which provides direct information
concerning the protein secondary structure label-free. Therefore,
we developed an attenuated total reflection Fourier transform infrared
spectroscopy (ATRāFTIR) sensor, which uses surface bound antibodies
to immobilize a desired target protein. The secondary structure of
the protein can be evaluated based on the secondary structure sensitive
frequency of the amide I band. Direct information about the effect
of a drug candidate on the secondary structure distribution of the
total target protein fraction within the respective body fluid can
be detected by a frequency shift of the amide I band. Thereby, the
extent of the amide I shift is indicative for the compound efficiency.
The functionality of this approach was demonstrated by the quantification
of the effect of the drug candidate methylene blue on the pathogenic
misfolded tau protein as extracted from cerebrospinal fluid (CSF).
Methylene blue induces a shift from pathogenic folded Ī²-sheet
dominated to the healthy monomeric state. A similar effect was observed
for congo red on pathogenic AĪ² isoforms from CSF. In addition,
the effect of berberine on synthetic AĪ²<sub>1ā42</sub> is studied. Berberine seems to decelerate the aggregation process
of synthetic AĪ²<sub>1ā42</sub> peptides
Specific Substates of Ras To Interact with GAPs and Effectors: Revealed by Theoretical Simulations and FTIR Experiments
The oncogenic Ras
protein adopts various specific conformational
states to execute its function in signal transduction. The large number
of Ras structures obtained from X-ray and NMR experiments illustrates
the diverse conformations that Ras adopts. It is difficult, however,
to connect specific structural features with Ras functions. We report
the free-energy landscape of RasĀ·GTP based on extensive explicit
solvent simulations. The free-energy map clearly shows that the functional
state 2 of RasĀ·GTP in fact has two distinct substates, denoted
here as āTyr32<sub>in</sub>ā and āTyr32<sub>out</sub>ā. Unbiased MD simulations show that the two substrates interconvert
on the submicrosecond scale in solution, pointing to a novel mechanism
for RasĀ·GTP to selectively interact with GAPs and effectors.
This proposal is further supported by time-resolved FTIR experiments,
which demonstrate that Tyr32 destabilizes the RasĀ·GAP complex
and facilitates an efficient termination of Ras signaling
BoletĆn de Segovia: NĆŗmero 115 - 1910 septiembre 26
Copia digital. Madrid : Ministerio de Cultura. SubdirecciĆ³n General de CoordinaciĆ³n Bibliotecaria, 200
Unraveling the Phosphocholination Mechanism of the <i>Legionella pneumophila</i> Enzyme AnkX
The
intracellular pathogen <i>Legionella pneumophila</i> infects
lung macrophages and injects numerous effector proteins
into the host cell to establish a vacuole for proliferation. The necessary
interference with vesicular trafficking of the host is achieved by
modulation of the function of Rab GTPases. The effector protein AnkX
chemically modifies Rab1b and Rab35 by covalent phosphocholination
of serine or threonine residues using CDP-choline as a donor. So far,
the phosphoryl transfer mechanism and the relevance of observed autophosphocholination
of AnkX remained disputable. We designed tailored caged compounds
to make this type of enzymatic reaction accessible for time-resolved
Fourier transform infrared difference spectroscopy. By combining spectroscopic
and biochemical methods, we determined that full length AnkX is autophosphocholinated
at Ser521, Thr620, and Thr943. However, autophosphocholination loses
specificity for these sites in shortened constructs and does not appear
to be relevant for the catalysis of the phosphoryl transfer. In contrast,
transient phosphocholination of His229 in the conserved catalytic
motif might exist as a short-lived reaction intermediate. Upon substrate
binding, His229 is deprotonated and locked in this state, being rendered
capable of a nucleophilic attack on the pyrophosphate moiety of the
substrate. The proton that originated from His229 is transferred to
a nearby carboxylic acid residue. Thus, our combined findings support
a ping-pong mechanism involving phosphocholination of His229 and subsequent
transfer of phosphocholine to the Rab GTPase. Our approach can be
extended to the investigation of further nucleotidyl transfer reactions,
which are currently of reemerging interest in regulatory pathways
of hostāpathogen interactions
Label-Free Raman Spectroscopic Imaging Monitors the Integral Physiologically Relevant Drug Responses in Cancer Cells
Predictions about the cellular efficacy
of drugs tested <i>in vitro</i> are usually based on the
measured responses of
a few proteins or signal transduction pathways. However, cellular
proteins are highly coupled in networks, and observations of single
proteins may not adequately reflect the <i>in vivo</i> cellular
response to drugs. This might explain some large discrepancies between <i>in vitro</i> drug studies and drug responses observed in patients.
We present a novel <i>in vitro</i> marker-free approach
that enables detection of cellular responses to a drug. We use Raman
spectral imaging to measure the effect of the epidermal growth factor
receptor (EGFR) inhibitor panitumumab on cell lines expressing wild-type
Kirsten-Ras (K-Ras) and oncogenic K-Ras mutations. Oncogenic K-Ras
mutation blocks the response to anti-EGFR therapy in patients, but
this effect is not readily observed <i>in vitro</i>. The
Raman studies detect large panitumumab-induced differences <i>in vitro</i> in cells harboring wild-type K-Ras as seen in A
in red but not in cells with K-Ras mutations as seen in B; these studies
reflect the observed patient outcomes. However, the effect is not
observed when extracellular-signal-regulated kinase phosphorylation
is monitored. The Raman spectra show for cells with wild-type K-Ras
alterations based on the responses to panitumumab. The subcellular
component with the largest spectral response to panitumumab was lipid
droplets, but this effect was not observed when cells harbored K-Ras
mutations. This study develops a noninvasive, label-free, <i>in vitro</i> vibrational spectroscopic test to determine the
integral physiologically relevant drug response in cell lines. This
approach opens a new field of patient-centered drug testing that could
deliver superior patient therapies
Additional file 3 of Fully automated registration of vibrational microspectroscopic images in histologically stained tissue sections
Tissue Microarray Registration Results. Detailed registration results of 56 FTIR vs. H&E TMA cores. (PDF 46387.2 kb