3 research outputs found
The PipX Protein, When Not Bound to Its Targets, Has Its Signaling CāTerminal Helix in a Flexed Conformation
PipX,
an 89-residue protein, acts as a coactivator of the global
nitrogen regulator NtcA in cyanobacteria. NtcAāPipX interactions
are regulated by 2-oxoglutarate (2-OG), an inverse indicator of the
ammonia abundance, and by P<sub>II</sub>, a protein that binds to
PipX at low 2-OG concentrations. The structure of PipX, when bound
to NtcA or P<sub>II</sub>, consists of an N-terminal, five-stranded
Ī²-sheet (conforming a Tudor-like domain), and two long Ī±-helices.
These helices adopt either a <i>flexed conformation</i>,
where they are in close contact and in an antiparallel mutual orientation,
also packing against the Ī²-sheet, or an <i>open conformation</i> (observed only in the P<sub>II</sub>āPipX complex) where
the last Ī±-helix moves apart from the rest of the protein. The
aim of this work was to study the structure and dynamics of isolated
PipX in solution by NMR. The backbone chemical shifts, the hydrogen-exchange,
and the NOE patterns indicated that the isolated, monomeric PipX structure
was formed by an N-terminal five-stranded Ī²-sheet and two C-terminal
Ī±-helices. Furthermore, the observed NOEs between the two helices,
and of Ī±-helix2 with Ī²-strand2 suggested that PipX adopted
a <i>flexed conformation</i>. The Ī²-strands 1 and
5 were highly flexible, as shown by the lack of interstrand backboneābackbone
NOEs; in addition, the <sup>15</sup>N-dynamics indicated that the
C terminus of Ī²-strand4 and the following Ī²-turn (Phe42-Thr47),
and the C-cap of Ī±-helix1 (Arg70-Asn71) were particularly mobile.
These two regions could act as hinges, allowing PipX to interact with
its partners, including PlmA in the newly recognized P<sub>II</sub>āPipXāPlmA ternary complex
Cā2 Thiophenyl Tryptophan Trimers Inhibit Cellular Entry of SARS-CoVā2 through Interaction with the Viral Spike (S) Protein
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
causes COVID-19, by infecting cells via the interaction of its spike
protein (S) with the primary cell receptor angiotensin-converting
enzyme (ACE2). To search for inhibitors of this key step in viral
infection, we screened an in-house library of multivalent tryptophan
derivatives. Using VSV-S pseudoparticles, we identified compound 2 as a potent entry inhibitor lacking cellular toxicity. Chemical
optimization of 2 rendered compounds 63 and 65, which also potently inhibited genuine SARS-CoV-2 cell
entry. Thermofluor and microscale thermophoresis studies revealed
their binding to S and to its isolated receptor binding domain (RBD),
interfering with the interaction with ACE2. High-resolution cryoelectron
microscopy structure of S, free or bound to 2, shed light
on cell entry inhibition mechanisms by these compounds. Overall, this
work identifies and characterizes a new class of SARS-CoV-2 entry
inhibitors with clear potential for preventing and/or fighting COVID-19
Cā2 Thiophenyl Tryptophan Trimers Inhibit Cellular Entry of SARS-CoVā2 through Interaction with the Viral Spike (S) Protein
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
causes COVID-19, by infecting cells via the interaction of its spike
protein (S) with the primary cell receptor angiotensin-converting
enzyme (ACE2). To search for inhibitors of this key step in viral
infection, we screened an in-house library of multivalent tryptophan
derivatives. Using VSV-S pseudoparticles, we identified compound 2 as a potent entry inhibitor lacking cellular toxicity. Chemical
optimization of 2 rendered compounds 63 and 65, which also potently inhibited genuine SARS-CoV-2 cell
entry. Thermofluor and microscale thermophoresis studies revealed
their binding to S and to its isolated receptor binding domain (RBD),
interfering with the interaction with ACE2. High-resolution cryoelectron
microscopy structure of S, free or bound to 2, shed light
on cell entry inhibition mechanisms by these compounds. Overall, this
work identifies and characterizes a new class of SARS-CoV-2 entry
inhibitors with clear potential for preventing and/or fighting COVID-19