Heras - Bacterial virulence factors: structure and function
The last few decades have witnessed an explosion in the rates of antibiotic resistant bacterial infections. Meanwhile, the antibiotics development pipeline has declined; only two new antibiotics have been approved since 2009. The World Health Organization (WHO) has recently released a report stating that "antimicrobial resistance poses a catastrophic threat" and urging governments to introduce initiatives to tackle bacterial infections to avoid returning to the pre-antibiotic era where bacterial infections were virtually untreatable.
Our research program examines the molecular mechanisms underlying Gram-negative bacterial infections. We use a multidisciplinary approach combining X-ray crystallography, molecular biology and biochemistry to investigate the structure-function relationships in proteins involved in bacterial pathogenesis and develop antibacterial drugs with novel modes of action.
Biogenesis of virulence factors
Bacteria utilise folding enzymes to assemble proteins that are essential for cell integrity and to produce functional virulence factors. These foldases include the Dsb family of proteins, which catalyse a key step in the protein-folding pathway: the introduction of disulfide bonds. The Dsb oxidative systems are present in numerous bacterial species and are central mediators of virulence. They play a crucial part in the biogenesis of virulence factors, including proteins associated with adhesion (e.g. fimbriae), host cell manipulation (e.g. toxins) and cellular spread (e.g. flagella). Mutants defective in the Dsb pathways have reduced fitness and attenuated virulence. In this context, we have two major topics that we investigate both of which are aimed at increasing our understanding of the biology of bacterial pathogens.
First we decipher the molecular mechanisms through which a number of bacteria catalyse the oxidative folding of proteins involved in virulence. Our studies have revealed cryptic structural variations among different homologues of these folding catalysts that may play a key role in their function.
Second, we work towards the development of a new class of antimicrobial agents by inhibiting these redox pathways. We use structural approaches to identify compounds that bind and inhibit the activity of these crucial enzymes.
Structural biology of key virulence factors: autotransporter proteins
Bacterial pathogens deploy an arsenal of virulence factors to establish infection and cause disease. At the forefront of the infection process are bacterial surface components, which are responsible for host colonisation and pathogen adhesion. An important group of surface proteins are autotransporter proteins. Autotransporters are the largest group of outer membrane and secreted proteins in bacteria. They are involved in cell adhesion, toxicity and promote the formation of aggregated communities and biofilms, which are critical strategies bacteria use to resist the host immune response and antibiotics. Furthermore, autotransporter proteins are also highly immunogenic and are integral components of human vaccines.
Despite their central role in bacterial pathogenesis and their potential for vaccine development, the three-dimensional structure of most autotransporter proteins has not been characterized and the precise molecular mechanism of how these proteins function is still unknown. Our research focuses on the architecture and mode of action of autotransporter proteins from pathogenic bacteria. We investigate the structural diversity of this family of proteins to identify the features that impart functionality. In this context we have recently elucidated the architecture of Ag43, an autotransporter protein that self-associates forming bacterial aggregates and biofilms. We have also shown how the autotransporter called UpaB contributes to bacterial colonization by binding to ECM proteins and glycosaminoglycans.
Our studies have shown unprecedented details of how these proteins work in infection. Identification of the structural determinants underlying autotransporter function will not only define functional epitopes but will be the basis for the development of strategies that block their function.
Meet the team
Compositions and methods for reducing bacterial aggregation: New Australian Provisional Patent Application 2018903096
Compositions and methods for reducing bacterial aggregation: Australian Patent Application No. 2018903096 | ME Ref: 1254742 [ME-ME.FID5118631]