25 research outputs found
Tuning the drug efflux activity of an ABC transporter in vivo by in vitro selected DARPin binders.
ABC transporters use the energy from binding and hydrolysis of ATP to import or extrude substrates across the membrane. Using ribosome display, we raised designed ankyrin repeat proteins (DARPins) against detergent solubilized LmrCD, a heterodimeric multidrug ABC exporter from Lactococcus lactis. Several target-specific DARPin binders were identified that bind to at least three distinct, partially overlapping epitopes on LmrD in detergent solution as well as in native membranes. Remarkably, functional screening of the LmrCD-specific DARPin pools in L. lactis revealed three homologous DARPins which, when generated in LmrCD-expressing cells, strongly activated LmrCD-mediated drug transport. As LmrCD expression in the cell membrane was unaltered upon the co-expression of activator DARPins, the activation is suggested to occur at the level of LmrCD activity. Consistent with this, purified activator DARPins were found to stimulate the ATPase activity of LmrCD in vitro when reconstituted in proteoliposomes. This study suggests that membrane transporters are tunable in vivo by in vitro selected binding proteins. Our approach could be of biopharmaceutical importance and might facilitate studies on molecular mechanisms of ABC transporters
Drug‐dependent inhibition of nucleotide hydrolysis in the heterodimeric ABC multidrug transporter PatAB from Streptococcus pneumoniae
Funder: Croucher Foundation; Id: http://dx.doi.org/10.13039/501100001692The bacterial heterodimeric ATP-binding cassette (ABC) multidrug exporter PatAB has a
critical role in conferring antibiotic resistance in multidrug-resistant infections by
Streptococcus pneumoniae. As with other heterodimeric ABC exporters, PatAB contains
two transmembrane domains that form a drug translocation pathway for efflux and two
nucleotide-binding domains that bind ATP, one of which is hydrolysed during transport.
The structural and functional elements in heterodimeric ABC multidrug exporters that
determine interactions with drugs and couple drug binding to nucleotide hydrolysis are
not fully understood. Here, we used mass spectrometry techniques to determine the subunit stoichiometry in PatAB in our lactococcal expression system and investigate
locations of drug binding using the fluorescent drug-mimetic azido-ethidium. Surprisingly,
our analyses of azido-ethidium-labelled PatAB peptides point to ethidium binding in the
PatA nucleotide-binding domain, with the azido moiety crosslinked to residue Q521 in the
H-like loop of the degenerate nucleotide-binding site. Investigation into this compound
and residue’s role in nucleotide hydrolysis pointed to a reduction in the activity for a
Q521A mutant and ethidium-dependent inhibition in both mutant and wild type. Most
transported drugs did not stimulate or inhibit nucleotide hydrolysis of PatAB in detergent
solution or lipidic nanodiscs. However, further examples for ethidium-like inhibition were
found with propidium, novobiocin and coumermycin A1, which all inhibit nucleotide
hydrolysis by a non-competitive mechanism. These data cast light on potential
mechanisms by which drugs can regulate nucleotide hydrolysis by PatAB, which might
involve a novel drug binding site near the nucleotide-binding domains
Study of W boson production in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV
A measurement is presented of W-boson production in PbPb collisions carried
out at a nucleon-nucleon (NN) centre-of-mass energy sqrt(s[NN]) of 2.76 TeV at
the LHC using the CMS detector. In data corresponding to an integrated
luminosity of 7.3 inverse microbarns, the number of W to mu mu-neutrino decays
is extracted in the region of muon pseudorapidity abs(eta[mu])<2.1 and
transverse momentum pt[mu]>25 GeV. Yields of muons found per unit of
pseudorapidity correspond to (159 +/- 10 (stat.) +/- 12 (syst.)) 10E-8 W(plus)
and (154 +/- 10 (stat.) +/- 12 (syst.)) 10E-8 W(minus) bosons per minimum-bias
PbPb collision. The dependence of W production on the centrality of PbPb
collisions is consistent with a scaling of the yield by the number of
incoherent NN collisions. The yield of W bosons is also studied in a sample of
pp interactions at sqrt(s)= 2.76 TeV corresponding to an integrated luminosity
of 231 inverse nanobarns. The individual W(plus) and W(minus) yields in PbPb
and pp collisions are found to agree, once the neutron and proton content in Pb
nuclei is taken into account. Likewise, the difference observed in the
dependence of the positive and negative muon production on pseudorapidity is
consistent with next-to-leading order perturbative QCD calculations.Comment: Submitted to Physics Letters
DARPin expression does not significantly alter expression of LmrCD proteins.
<p>(<b>A</b>, <b>B</b>) A V5-tag was introduced in frame at the 5′-end of genomic <i>lmrD</i> in <i>L. lactis</i> (denoted <i>L. lactis NZ9000 lmrD<sub>V5</sub></i>). Plasmid-encoded DARPin activators or the control DARPin E3_5* were expressed in <i>L. lactis NZ9000 lmrD<sub>V5</sub></i> in the presence and absence of daunomycin (14 µM for DARPin_Act3 and E3_5* and 28 µM for DARPin_Act1 and DARPin_Act2, respectively). The expression levels of genomic LmrD<sub>V5</sub> were then quantified by comparing the Western blot signal obtained using an anti-V5 antibody (A) with total protein detected by SYPRO ruby staining (B). (<b>C</b>) The relative amounts of LmrD<sub>V5</sub> expression were quantified by densitometry. Each bar represents the average of three independent data points (n = 3) of which one data point is shown in (A) and (B).</p