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Prediction of b-lactams
position and orientation in the central cavity of the component of
bacterial AcrAB-TolC multidrug efflux pump AcrB
Ferreira M. M. C. and Kiralj R.
Universidade Estadual de Campinas - Campinas SP
Resumo [Abstract]
Multidrug resistance of microbes and parasites as
well as of cancer cells to currently used drugs
is becoming one of the
major problems in combating infectious
and parasitic diseases and cancer, respectively.
Among major mechanisms of
multidrug resistance in cellular microbes and
cancer cells are efflux pumps, mono-
or polycomponent macromolecular
systems that extrude drugs and a large
variety of structurally dissimilar substances
from cell into the ouside medium.
Bacterial efflux pump AcrAB-TolC exists in E. coli,
S.
typhimurium and several other Gram-negative bacteria as their major
efflux system, being effective against b-lactams
and other antibiotics, organic dyes, detergents and
many xenobiotics. It
is a proton-motive device that connects the
inner and outer cell membranes. The pump
consists of the tube-like TolC
trimer, the jellyfish-like AcrB trimer, and the
AcrA oligomer (3D structure for this component
is not known). The AcrB
component is responsible for attraction of
substrates that are coming from periplasm/cytoplasm,
their accumulation in its
central cavity, and their expulsion through
its channel and the TolC channel. Proton
influx induces a series of allosteric
changes in the pump and its components, enabling opening
of the channels. Substrates in the central cavity must be
placed
and oriented in appropriate way to be extruded.
The substrate position and orientation depend on their molecular
properties
and previous interaction with the AcrB
opening (vestibule) and the outer membrane.
In this work, these relationships
have been studied at quantitative level. Experimental
3D structures of four AcrB-drug complexes (dequalinium,
ethidium,
ciprofloxacin and ethidium [1]) were used.
The drug-protein geometry and stereoelectronic molecular
properties of these
drugs and of 16 b-lactams
enabled prediction of positional and orientational parameters
of these b-lactams placed inside
AcrB [2]. Crystallographc C3
symmetry of AcrB (space group R32) facilitated
definition of AcrB crucial axes and points,
as well as drug-central cavity
distance and angle parameters. Drug molecular descriptors
that quantitatively correlated
with these parameters were principal moments
of inertia, molecular box parameters, dipole moment
and its components,
polarizability and hyperpolarizabilities.
The new AcrB-drug complexes show that drugs
interact with the vestibule by
electrostatic interactions, beforebinding
in the central cavity and turning with
their positive ends toward the opening
of the AcrB channel. These results
are consistent with known pump-mediated drug efflux mechanism
and our previous
quantitative structure-activity studies [3].
Agradecimentos [Acknowledgement]
FAPESP
Referências [References]
1. E. W. Yu et al., Science 300, 976 (2003)
2. M. M. C. Ferreira, R. Kiralj, J. Mol. Graph. Mod.,
submitted
3. M. M. C. Ferreira, R. Kiralj, J. Chemometr. 18, 242
(2004)
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