Research Description:
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The focus of research in this laboratory is on understanding function of membrane
transport proteins. Transport of nutrients into or toxic substances out of the
cell is integral to life, and is carried out by dedicated proteins located in
the cell membrane. Most transport processes require input of energy - either in
the form of ATP or membrane potential. When ATP is the source of energy, transport
also requires the function of a dedicated ATPase. Four major classes of transport
ATPases are known: F, A, P, and ABC. The molecular mechanisms of transport ATPases
are poorly understood. It is not known how the energy is transduced to carry out
transport, or what determines the polarity of transport. An intriguing question
also concerns the substrate specificty of the transport proteins.
Most transporters are able to carry out transport of only one or a set of
related substrates. Recently, a class of transporters called multidrug resistance
(MDR) proteins that can recognize a variety of structurally unrelated substrates,
has been discovered in both prokaryotic and eukaryotic cells. An MDR protein,
called P-glycoprotein (Pgp), brings about efflux of anticancer drugs from cancer
cells resulting in resistance, which can be a major clinical problem. What allows
these proteins to recognize several substrates, and how did these proteins evolve?
We are analyzing one transporter (DrrAB) from bacteria that might be evolutionarily
very close to the ancestral form of the MDR protein found in cancer cells. This
system confers resistance to an anticancer drug doxorubicin in Streptomyces
peucetius.
Streptomyces is also the producer organism for this antibiotic. It has been
hypothesized that resistance in this organism to its own antibiotic is the result
of an efflux mechanism similar to the one employed by Pgp. Pgp and DrrAB show
homology at the level of the amino acid sequence; both ATPases belong to the
ABC family of transporters. Hence, structure/function analysis and analysis
of the drug binding sites in DrrAB will help elucidate how Pgp functions and
how it might have evolved. A second project investigates the mechanism of function
of an anion transport protein (A-type ATPase) from E. coli. Efflux of arsenite
and antimonite by this ATPase (ArsATPase) results in resistance to these toxic
oxyanions in E. coli. Focus of this project is on understanding the biochemical
mechanism of catalysis by the ATPase and how energy is transduced to allow opening
and closing of the channel. To address questions related to interaction between
subunits of the transporter, a variety of molecular and genetic techniques,
including mutagenesis, suppressor analysis, and complementation are being used.
The Plasmid-Encoded Anion Pump.
Recent Publications:
Rao, DK., and Kaur. P. The Q-loop of DrrA is involved in Producing the Closed Conformation of the Nucleotide Binding Domains and in Transduction of Conformational Changes between DrrA and DrrB. Biochemistry. 47: 3038-3050, 2008.
Kaur, P., Rao, DK., and Gandlur, SM. Biochemical characterization of domains in the membrane subunit DrrB that interact with the ABC subunit DrrA: identification of a conserved motif. Biochemistry. 44: 2661-2670, 2005.
Gandlur SM, Wei, L, Levine, J, Russell, J, and Kaur, P. Membrane topology of the DrrB protein of the doxorubicin transporter Streptomyces peucetius. J. Biol. Chem. 279:27799-27806, 2004
Jia, H., and Kaur, P. Biochemical evidence for interaction between the two nucleotide binding domains of ArsA: Insights from mutants and ATP analogs. J. Biol. Chem. 278:6603-6609, 2003.
Kaur, P. Multidrug resistance: can different keys open the same lock? (Perspectives article) Drug Resistance Updates 5:61-64, 2002.
See more publications >>
Grant Support:
National Institutes of Health 2002-2006
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