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Network of proteins involved in antibiotic resistance
than FadL and OmpW in response to SM resistance,” explains Peng. “The function of LamB is opposite to that of Sniffle, sniffle. Cough, cough. A throat TolC; it elevates the resistance when so sore you cannot bear to swallow. deleted.” Maybe you have a cold. “How could I Next, the researchers created SMhave picked up another cold this searesistant versions of the deletion son?” you wonder. “I even washed my strains. With these strains, “we may hands with antibiotic soap several detect changes when one of the functimes every day.” You go to the doctor tional proteome genes is deleted,” exand plead for another antibiotic preplains Peng. scription, and “From these she reluctantly changes, we may complies. The know which promedicine does teins compensate not help, and for the function you are beginof the deleted ning to develop protein.” Again, additional sympthe MIC and surtoms. What is vivability assays going on? First, were performed. colds are caused From these by viruses, and analyses, the antibiotics will team deduced not combat a that FadL, TolC, viral infection. Far-reaching effects. The gene for the protein at the start of each arrow is deleted, and the affected protein is found at the end of the arrow. Proteins (a) up-regulated or (b) down-regulated in response to and OmpT are Second, if you the deletion of particular OM proteins are shown. important for the overused antibiselection of SMotics in the past, resistant E. coli you may have strains. selected for the Finally, OM proteins were isolated entially expressed in the strains. From growth of an antibiotic-resistant strain from the resistant and nonresistant dethese spots, seven unique proteins were of bacteria in your body. letion strains. Western blots were peridentified, and six of these proteins were The inappropriate and all-too-freformed to assay the effect of a deletion known to be present in the OM. TolC, quent use of antibiotics has led to “suon the levels of the other OM proteins. OmpT, and LamB were up-regulated, perbugs”, bacteria that have become “In this way, we may profile a network, whereas FadL, OmpW, and Dps were resistant to known antibiotics. To betand from this network, we understand down-regulated in the resistant strain. ter understand this growing publicthe roles of every protein,” says Peng. The identities and expression levels of health problem, Xuan-Xian Peng and For example, the fact that the expresthese proteins were validated. co-workers at Sun Yat-sen University sion level of TolC was not affected by To better assess the roles of these (China) studied the outer membrane the deletion of the other proteins indiproteins in normal antibiotic suscepti(OM) proteins of a model bacterium, E. cates that TolC may be an upstream bility, the investigators constructed a coli, after it grew resistant to streptoprotein in the pathway. On the basis of series of strains in which one of the mycin (SM), an antibiotic that is comthese data, the team put together two identified OM proteins was deleted monly overprescribed. In JPR (DOI possible functional networks, dependfrom the original control strain. All of 10.1021/pr800310y), the researchers ing on whether the deletion of an OM the strains were grown in various conreport the identities of several key gene results in the up- or down-regulacentrations of SM to determine the players in this process and discuss how tion of another OM protein. MIC and survivability of the deletion these proteins could make a bacterial The researchers have a lot of work on strains. Half of the deletion strains strain resistant to antibiotics. their plates to more definitively figure gave the expected results, but deletion In the study, the team focused on out the roles of each OM protein. Specifof FadL and OmpW had no effect. UnOM proteins because “they are barriers ically, they now are focusing on the expectedly, when LamB (an up-reguagainst the movement of antibiotics analysis of protein-protein interactions lated protein in resistant bacteria) was into the cytoplasm and [they serve as] in the hope of defining protein comdeleted, the bacteria grew more resischannels for the removal of antibiotics plexes that contribute to resistance. tant instead of more susceptible. out of cells,” explains Peng. To obtain “These results may tell us that TolC, a resistant E. coli strain for the investi—Katie Cottingham OmpT, and Dps are more important gation, the scientists grew a control
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strain in SM for 10 successive rounds at an SM concentration that was half the minimum inhibitory concentration (1/2 MIC). To some extent, this condition mimics a low-level, repeated use of an antibiotic, says Peng. Resistant and control strains were cultured separately, and OM proteins were enriched. Next, the proteins were separated by 2DE. Various spots were differ-
Journal of Proteome Research • Vol. 7, No. 9, 2008
10.1021/pr800470w
© 2008 American Chemical Society
