Graduate Studies Faculty
Georgiana E. Purdy, Ph.D.
Programs:Molecular Microbiology & Immunology
Program in Molecular & Cellular Biosciences
Research Interests:Bacterial pathogenesis, Tuberculosis, Macrophage biology, Innate immunity » Click here for more about Dr. Purdy's research » PubMed Listing
Preceptor RotationsDr. Purdy has not indicated availability for preceptor rotations at this time.
Faculty MentorshipDr. Purdy has not indicated availability as a mentor at this time.
The goal of the Purdy Lab is to further define the dynamic interface between the human pathogen Mycobacterium tuberculosis and the host macrophage. Tuberculosis has re-emerged as a global health concern. The World Health Organization estimates that Mycobacterium tuberculosis (Mtb) infects one third of the world population.
M. tuberculosispossesses several mechanisms to resist environmental stresses imposed by the host immune system. Current projects focus on 1) defining the mechanisms by which mycobacteria respond to and resist the antimicrobial repertoire of the macrophage and 2) understanding the role of MmpL proteins in the biosynthesis of the Mtb cell wall.
1) The ability to survive and multiply within the host macrophage is key to its pathogenesis. In resting macrophages, the bacterium arrests phagosome maturation and replicates in a compartment that resembles early endosomes. Activated macrophages promote clearance of mycobacteria through both non-oxidative and oxidative mechanisms: In activated macrophages there is increased fusion of the mycobacteria-containing vacuole with the lysosome where Ubiquitin-derived peptides (Ub-peptides) contribute to the bactericidal activity of the lysosome. Activation also triggers the production of reactive oxygen and nitrogen intermediates (ROI and RNI). Our work indicates that Ub-peptides act by physically interacting with mycobacterial membranes. This interaction disrupts the bacterial proton motive force and results in bacterial death (Purdy et al., 2009; Foss et al., 2012).
2) The cell wall plays a crucial role in the Mtb host pathogen interface on several levels. The mycobacterial cell wall confers intrinsic resistance to external stresses including the host immune response and antibiotics. Mycobacterial cell wall lipids also contribute to biofilm formation. Genetic and biochemical studies have made great strides in the characterization of the mycobacterial cell wall. However, gaps remain in our knowledge: We have not identified all of the cell wall lipids, defined their biochemical pathways, or ascertained their importance in conditions mimicking those encountered during infection of the host. Recent work demonstrates that the Mycobacterial membrane protein large (MmpL) proteins transport lipids to the mycobacterial cell wall. The mechanisms underlying MmpL transporter function and their respective substrates are not fully elucidated. MmpL3 is essential and MmpL4, MmpL5, MmpL7, MmpL8 and MmpL11 contribute to Mtb virulence. Our work demonstrated MmpL11 transports the mycolic acid-containing lipids monomeromycolyl diacylglycerol (MMDAG) and wax ester mycolate (WE) to the M. smegmatis cell wall (Pacheco et al., 2013). Biofilm formation by the M. smegmatis mmpL11 mutant was impaired, but was complemented by expression of either M. smegmatis MmpL11 or MmpL11TB, emphasizing that MmpL11 has a conserved function in mycobacteria. We are continuing to investigate how the conserved mycolic-acid containing lipid transporters MmpL3 and MmpL11 function.
Dr. Purdy is accepting rotation students. Students who join the Purdy laboratory can expect to gain experience in a wide range of techniques. Most research projects will include some or all of the following:
Genomic analyses: We use DNA microarrays and bioinformatic approaches to define mycobacterial stress response regulons.
Bacterial and molecular genetics: Our approaches include transposon mutant screens to identify Mtb mutants with specific phenotypes and site-directed mutagenesis of proteins of interest.
Biochemistry: We routinely perform protein purification and are characterizing the function of several classes of proteins. In addition, we use chromatography, mass spectroscopy and differential scanning calorimetry to better understand the architecture and composition of the mycobacterial cell wall.
Immunobiology: We routinely assess the ability of wild type and mutant Mtb strains to infect macrophages. We use microscopy to define the niche established by the bacterium in these immune cells and we use functional readouts such as cytokine ELISAs to assess the response of macrophages to infection. We use cell biology techniques to study the mycobactericidal properties of macrophages.
Structural biology: These are largely ongoing studies in collaboration with other groups. We will determine the structure of host antimicrobial peptides that kill Mtb and other bacterial pathogens. We will determine the structure of membrane transporters that are important for Mtb survival in environmental stresses and the host environment.
Selected Recent Publications
Pacheco, S.A., F.F. Hsu, K.M. Powers, and G.E. Purdy. 2013. The MmpL11 transporter contributes to mycobacterial cell wall biosynthesis and biofilm formation in M. smegmatis.J. Biol. Chem.288:24213-24222. PMID 238369904.
Purdy, G.E., Pacheco, S.A., Turk, J., and F.F. Hsu. 2013. Characterization of mycobacterial triacylglycerols and the unusual monomeromycolyl diacylglycerols from Mycobacterium smegmatis biofilms by linear ion-trap multiple-stage and high-resolution mass spectrometry with electrospray ionization. Anal. Bioanal. Chem. 405(23), 7415–26. PMID: 23852148
Pacheco, S.A., Powers, K.M., Engelmann, Messaoudi, I. and G.E. Purdy. 2013. Autophagic killing effects against Mycobacterium tuberculosis by alveolar macrophages from young and aged Rhesus macaque. PLoS ONE8(6):e66985. doi:10.1371/journal.pone.0066985. PMID 23825603
Foss, M.H., Powers, K. M., and G.E. Purdy. 2012. Structural and functional characterization ofmycobactericidal ubiquitin-derived peptides in model and bacterial membranes. Biochemistry, 51(49):9922-9. PMID:23173767 PMC3567233
Hsu,F.F., Pacheco, S., Turk, J. and G. Purdy. 2012. Structural Elucidation of Glycopeptidolipid of Mycobacterium smegmatis by High Resolution Multiple-stage Linear Ion-trap Mass Spectrometry with Electrospray Ionization, J Mass Spectrom. 47(10):1269-81. PMID: 23019158 PMC3462375
Harriff, M.,Purdy, G.E. and D.M. Lewinsohn. 2012. Escape from the phagosome: the explanation for MHC-I processing of mycobacterial antigen? Front. Immun.3:40. doi: 10.3389/fimmu.2012.00040. PMID: 22566923 PMC3342008
Daugherty, A. K.M. Powers, M.S. Standley, C.S. Kim, and G.E. Purdy. 2011. M. smegmatis RoxY is a repressor of oxyS and contributes to resistance to oxidative stress and bactericidal ubiquitin peptides. J. Bacteriol. 193(24):6824-33. PMID: 21984791. PMC3232828