14 research outputs found
Structural Studies of Inhibitors with Clinically Relevant Influenza Endonuclease Variants
Vital to the treatment of influenza is the use of antivirals
such
as Oseltamivir (Tamiflu) and Zanamivir (Relenza); however, antiviral
resistance is becoming an increasing problem for these therapeutics.
The RNA-dependent RNA polymerase acidic N-terminal (PAN) endonuclease, a critical component of influenza viral replication
machinery, is an antiviral target that was recently validated with
the approval of Baloxavir Marboxil (BXM). Despite its clinical success,
BXM has demonstrated susceptibility to resistance mutations, specifically
the I38T, E23K, and A36 V mutants of PAN. To better understand
the effects of these mutations on BXM resistance and improve the design
of more robust therapeutics, this study examines key differences in
protein–inhibitor interactions with two inhibitors and the
I38T, E23K, and A36 V mutants. Differences in inhibitor binding were
evaluated by measuring changes in binding to PAN using
two biophysical methods. The binding mode of two distinct inhibitors
was determined crystallographically with both wild-type and mutant
forms of PAN. Collectively, these studies give some insight
into the mechanism of antiviral resistance of these mutants
Reorientation of the Methyl Group in MAs(III) is the Rate-Limiting Step in the ArsM As(III) <i>S</i>‑Adenosylmethionine Methyltransferase Reaction
The
most common biotransformation of trivalent inorganic arsenic
(As(III)) is methylation to mono-, di-, and trimethylated species.
Methylation is catalyzed by As(III) <i>S</i>-adenosylmethionine
(SAM) methyltransferase (termed ArsM in microbes and AS3MT in animals).
Methylarsenite (MAs(III)) is both the product of the first methylation
step and the substrate of the second methylation step. When the rate
of the overall methylation reaction was determined with As(III) as
the substrate, the first methylation step was rapid, whereas the second
methylation step was slow. In contrast, when MAs(III) was used as
the substrate, the rate of methylation was as fast as the first methylation
step when As(III) was used as the substrate. These results indicate
that there is a slow conformational change between the first and second
methylation steps. The structure of CmArsM from the thermophilic alga Cyanidioschyzon merolae sp. 5508 was determined with
bound MAs(III) at 2.27 Å resolution. The methyl group is facing
the solvent, as would be expected when MAs(III) is bound as the substrate
rather than facing the SAM-binding site, as would be expected for
MAs(III) as a product. We propose that the rate-limiting step in arsenic
methylation is slow reorientation of the methyl group from the SAM-binding
site to the solvent, which is linked to the conformation of the side
chain of a conserved residue Tyr70
Structure of an As(III) <i>S</i>-Adenosylmethionine Methyltransferase: Insights into the Mechanism of Arsenic Biotransformation
Enzymatic methylation of arsenic is a detoxification
process in
microorganisms but in humans may activate the metalloid to more carcinogenic
species. We describe the first structure of an As(III) <i>S</i>-adenosylmethionine methyltransferase by X-ray crystallography that
reveals a novel As(III) binding domain. The structure of the methyltransferase
from the thermophilic eukaryotic alga <i>Cyanidioschyzon merolae</i> reveals the relationship between the arsenic and <i>S</i>-adenosylmethionine binding sites to a final resolution of ∼1.6
Å. As(III) binding causes little change in conformation, but
binding of SAM reorients helix α4 and a loop (residues 49–80)
toward the As(III) binding domain, positioning the methyl group for
transfer to the metalloid. There is no evidence of a reductase domain.
These results are consistent with previous suggestions that arsenic
remains trivalent during the catalytic cycle. A homology model of
human As(III) <i>S</i>-adenosylmethionine methyltransferase
with the location of known polymorphisms was constructed. The structure
provides insights into the mechanism of substrate binding and catalysis
Structure of an As(III) <i>S</i>-Adenosylmethionine Methyltransferase: Insights into the Mechanism of Arsenic Biotransformation
Enzymatic methylation of arsenic is a detoxification
process in
microorganisms but in humans may activate the metalloid to more carcinogenic
species. We describe the first structure of an As(III) <i>S</i>-adenosylmethionine methyltransferase by X-ray crystallography that
reveals a novel As(III) binding domain. The structure of the methyltransferase
from the thermophilic eukaryotic alga <i>Cyanidioschyzon merolae</i> reveals the relationship between the arsenic and <i>S</i>-adenosylmethionine binding sites to a final resolution of ∼1.6
Å. As(III) binding causes little change in conformation, but
binding of SAM reorients helix α4 and a loop (residues 49–80)
toward the As(III) binding domain, positioning the methyl group for
transfer to the metalloid. There is no evidence of a reductase domain.
These results are consistent with previous suggestions that arsenic
remains trivalent during the catalytic cycle. A homology model of
human As(III) <i>S</i>-adenosylmethionine methyltransferase
with the location of known polymorphisms was constructed. The structure
provides insights into the mechanism of substrate binding and catalysis
Recommended from our members
Structural Basis of Analog Specificity in PKG I and II
Cyclic
GMP analogs, 8-Br, 8-pCPT, and PET-cGMP, have been widely
used for characterizing cellular functions of cGMP-dependent protein
kinase (PKG) I and II isotypes. However, interpreting results obtained
using these analogs has been difficult due to their low isotype specificity.
Additionally, each isotype has two binding sites with different cGMP
affinities and analog selectivities, making understanding the molecular
basis for isotype specificity of these compounds even more challenging.
To determine isotype specificity of cGMP analogs and their structural
basis, we generated the full-length regulatory domains of PKG I and
II isotypes with each binding site disabled, determined their affinities
for these analogs, and obtained cocrystal structures of both isotypes
bound with cGMP analogs. Our affinity and activation measurements
show that PET-cGMP is most selective for PKG I, whereas 8-pCPT-cGMP
is most selective for PKG II. Our structures of cyclic nucleotide
binding (CNB) domains reveal that the B site of PKG I is more open
and forms a unique π/π interaction through Arg285 at β4
with the PET moiety, whereas the A site of PKG II has a larger β5/β6
pocket that can better accommodate the bulky 8-pCPT moiety. Our structural
and functional results explain the selectivity of these analogs for
each PKG isotype and provide a starting point for the rational design
of isotype selective activators
Additional file 1: Figure S1. of Structure of the catalytic domain of the colistin resistance enzyme MCR-1
Amino acid sequence alignment of phosphoethanolamine transferases MCR-1, EptC (C. jejuni), and LptA (N. meningitidis). (TIF 10272 kb
Carboxylic Acid Isostere Derivatives of Hydroxypyridinones as Core Scaffolds for Influenza Endonuclease Inhibitors
Among the most important influenza virus targets is the
RNA-dependent
RNA polymerase acidic N-terminal (PAN) endonuclease, which
is a critical component of the viral replication machinery. To inhibit
the activity of this metalloenzyme, small-molecule inhibitors employ
metal-binding pharmacophores (MBPs) that coordinate to the dinuclear
Mn2+ active site. In this study, several metal-binding
isosteres (MBIs) were examined where the carboxylic acid moiety of
a hydroxypyridinone MBP is replaced with other groups to modulate
the physicochemical properties of the compound. MBIs were evaluated
for their ability to inhibit PAN using a FRET-based enzymatic
assay, and their mode of binding in PAN was determined
using X-ray crystallography
Carboxylic Acid Isostere Derivatives of Hydroxypyridinones as Core Scaffolds for Influenza Endonuclease Inhibitors
Among the most important influenza virus targets is the
RNA-dependent
RNA polymerase acidic N-terminal (PAN) endonuclease, which
is a critical component of the viral replication machinery. To inhibit
the activity of this metalloenzyme, small-molecule inhibitors employ
metal-binding pharmacophores (MBPs) that coordinate to the dinuclear
Mn2+ active site. In this study, several metal-binding
isosteres (MBIs) were examined where the carboxylic acid moiety of
a hydroxypyridinone MBP is replaced with other groups to modulate
the physicochemical properties of the compound. MBIs were evaluated
for their ability to inhibit PAN using a FRET-based enzymatic
assay, and their mode of binding in PAN was determined
using X-ray crystallography
Neutron Diffraction Reveals Hydrogen Bonds Critical for cGMP-Selective Activation: Insights for cGMP-Dependent Protein Kinase Agonist Design
High selectivity of cyclic-nucleotide
binding (CNB) domains for
cAMP and cGMP are required for segregating signaling pathways; however,
the mechanism of selectivity remains unclear. To investigate the mechanism
of high selectivity in cGMP-dependent protein kinase (PKG), we determined
a room-temperature joint X-ray/neutron (XN) structure of PKG Iβ
CNB-B, a domain 200-fold selective for cGMP over cAMP, bound to cGMP
(2.2 Å), and a low-temperature X-ray structure of CNB-B with
cAMP (1.3 Å). The XN structure directly describes the hydrogen
bonding interactions that modulate high selectivity for cGMP, while
the structure with cAMP reveals that all these contacts are disrupted,
explaining its low affinity for cAMP
Implementing Fluorescence Anisotropy Screening and Crystallographic Analysis to Define PKA Isoform-Selective Activation by cAMP Analogs
Cyclic
AMP (cAMP) is a ubiquitous second messenger that regulates
many proteins, most notably cAMP-dependent protein kinase (PKA). PKA
holoenzymes (comprised of two catalytic (C) and two regulatory (R)
subunits) regulate a wide variety of cellular processes, and its functional
diversity is amplified by the presence of four R-subunit isoforms,
RIα, RIβ, RIIα, and RIIβ. Although these isoforms
all respond to cAMP, they are functionally nonredundant and exhibit
different biochemical properties. In order to understand the functional
differences between these isoforms, we screened cAMP derivatives for
their ability to selectively activate RI and RII PKA holoenzymes using
a fluorescence anisotropy assay. Our results indicate that RIα
holoenzymes are selectively activated by C8-substituted analogs and
RIIβ holoenzymes by N6-substituted analogs, where HE33 is the
most prominent RII activator. We also solved the crystal structures
of both RIα and RIIβ bound to HE33. The RIIβ structure
shows the bulky aliphatic substituent of HE33 is fully encompassed
by a pocket comprising of hydrophobic residues. RIα lacks this
hydrophobic lining in Domain A, and the side chains are displaced
to accommodate the HE33 dipropyl groups. Comparison between cAMP-bound
structures reveals that RIIβ, but not RIα, contains a
cavity near the N6 site. This study suggests that the selective activation
of RII over RI isoforms by N6 analogs is driven by the spatial and
chemical constraints of Domain A and paves the way for the development
of potent noncyclic nucleotide activators to specifically target PKA
iso-holoenyzmes