Antibiotics were first used to great effect in the 1930s. However, the last two decades has seen an increase in the drug resistance observed in clinical isolates and the emergence of multidrug resistant ‘superbugs’. The loss in efficacy of current antibiotics and a lack of new antibiotics in development ultimately threatens our ability to combat bacterial infections. We are investigating the contribution of membrane proteins to bacterial pathogenicity, as they are ideal targets for new antimicrobial strategies.
Our lab focuses on the role of ATP-binding cassette (ABC) transporters in facilitating bacterial pathogenesis. ABC transporters are found in all domains of life and comprise one of the largest protein superfamilies. In cells, ABC transporters facilitate unidirectional transport of compounds and are powered by ATP hydrolysis. This makes them excellent at moving compounds against their concentration gradients. Although ABC transporters in humans only move compounds out of cells, in bacteria they also provide crucial routes for the uptake of compounds as well. The work in our laboratory focuses on these ABC importers, also called ABC permeases, as they scavenge nutrients from the host environment during infection. These ABC permeases are also completely absent from humans making them ideal targets for future antibiotics.
The projects in our laboratory are focused on studying ABC transporters involved in metal ion uptake.
Metal Ion ABC Transporters of Pathogenic Bacteria
Bacterial infections are highly dependent on metal ion micronutrients. The high affinity uptake pathways are encoded for by ABC permeases that acquire metal ions from the extracellular environment. Of particular interest to our group are the metal ions manganese and zinc. Manganese has important roles during infection and colonization, where it serves in carbon metabolism and oxidative stress response whereas zinc is an essential cofactor for numerous cellular functions. The manganese and zinc ABC uptake transporters have been shown to be essential for the virulence of a number of human pathogens.
1. Manganese uptake in Streptococcus pneumoniae and other pathogens
Bacterial pathogens must scavenge their metal ions from the host environment in order to mediate virulence. Streptococcus pneumoniae is the world's foremost bacterial pathogen and is responsible for more than one million deaths every year. In terms of relative disease burden, it is the largest bacterial killer of young children and kills more children every year than AIDs, tuberculosis and malaria combined. However, its ability to infect and cause disease are dependent on the acquistion of metal ions, one of which is the transition row metal ion manganese. Loss of manganese uptake completely prevents its ability to cause disease.
Our group seeks to understand how S. pneumoniae, and other pathogens, scavenge manganese from the host environment. Although it was known an ABC importer was involved in this process, the underlying details were pooly understood. Recently we revealed the mechanism by which S. pneumoniae scavenges manganese from the host environment and how another metal ion, zinc, interfered with this process. We found that the manganese recruiting protein, PsaA, used a 'spring-hammer' mechanism to bind metal ions, in which half of the protein pivoted and closed over the other half (shown in this movie).
There are still many unanswered questions that we are currently investigating. These include how is this ABC importer is selective for manganese ions, how are these ions are translocated into the bacterial cell, and how does the host prevent manganese from being scavenged by the bacteria during infection. Answering these questions will provide the necessary information to design the next generation of antimicrobial agents to target this essential bacterial pathway.
2. Zinc homeostasis in Streptococcus pneumoniae
Zinc is the second most abundant transition row element in biological systems. This metal ion has crucial roles in numerous cellular processes such as transcription, translation, catalysis and metabolism. As with all nutrients, pathogenic bacteria must scavenge zinc from the host in order to mediate disease.
Our studies have shown that manganese and zinc have an unusual relationship in S. pneumoniae, where zinc can actually block the manganese ABC importer. So we are seeking to understand how zinc is acquired and managed in this organism. Recently work from our lab identified that zinc uptake in S. pneumoniae, although similar to manganese uptake, was regulated in a more complex manner. Intriguingly zinc was recruited by 2 proteins, AdcA and AdcAII. A number of possible models have been proposed for how these proteins work together to recruit zinc (one is presented in this movie).
Work in our group is focused on understanding how zinc is sensed by S. pneumoniae, how is zinc managed once it has been translocated into the cell, and how does the host utilise zinc during infection. The answers we obtain to these questions will lead to new ways to target this major human pathogen and its need for zinc.
Our research is supported by:
- National Health and Medical Research Council (NHMRC)
- Project Grant (CIB) - APP1080784 (2015-2017) $613,134
- Project Grant (CIA) - APP1022240 (2012-2014) $568,375
- Equipment Grant (CIA) - Liquid handling robotics - (2015) $20,000
- Equipment Grant (CIA) - Digital PCR equipment - (2014) $40,000
- Equipment Grant (CIA) - Spectrophotometric equipment - (2012) $35,500
- Equipment Grant (CIA) - Refrigerated AKTA FPLC - (2011) $62,042
- Equipment Grant (CIA) - Beckman Coulter Optima Max Biosafe Ultracentrifugation System - (2010) $78,000
- Equipment Grant (CID) - Cell disruptor system - (2009) $22,000
- Equipment Grant (CII) - Replacement Purification Systems - (2008) $28,401
- Australian Research Council (ARC)
- Discovery Project (CIB) - DP150104515 (2015-2017) $384,300
- Discovery Project (CIA) - DP120103957 (2012-2014) $255,000
- Channel 7 Children's Research Foundation
- Australian Cystic Fibrosis Foundation
- Postgraduate Studentship Grant - (2011-2013) $15,000
- Clive and Vera Ramaciotti Foundation
- Equipment Grant (Coordinator) - Zetasizer Nano ZSP for protein characterisation and drug discovery - (2013) $54,783
- Equipment Grant (Coordinator) - Instrumentation for cellular and subcellular analyses - (2012) $67,595
- University of Adelaide
- DVCR IRF Grant (CIA) Metalloproteomics infrastructure grant (Bioruptor) - (2015) $50,000
- DVCR IRF Grant (CIA) Metalloproteomics infrastructure grant (HPLC) - (2015) $28,000
- IPAS Extending Collaborations Pilot Projects (CIB) - (2014) $16,000
- IPAS Extending Collaborations Pilot Projects (CIB) - (2013) $8,500
- DVCR Equipment Grant (CIA) - Temperature controlled shaking incubators - (2012) $81,136
- DVCR Equipment Grant (CIA) - High speed centrifugation infrastructure - (2012) $365,813