Despite being the world’s most prevalent pathogen, Mycobacterium tuberculosis (MTB) is still a puzzle. The Grundner lab is working toward a better understanding of MTB virulence by studying secreted MTB virulence factors. Lab members determine their functions to learn about immunity and infection, with the ultimate goal of translating these findings into better therapies for tuberculosis.
Infections are characterized by complex interactions between host and pathogen. In the case of tuberculosis, the immune system and MTB strike a fine balance that allows MTB to survive in a latent state for many years without being cleared from the host. The Grundner lab studies factors through which MTB mutes the immune response, learning about both bacterial pathogenesis and the human immune system in the process.
The lab follows secreted MTB virulence factors into the host to define the host substrates and their precise function. Much of the lab’s work is focused on two signaling molecules: the tyrosine phosphatases (PTPs) PtpA and PtpB. Manipulation of host cell signaling by the PTPs is particularly effective because small changes in signal flows can have large physiologic effects. The Grundner lab combines microbiology, biochemistry, X-ray crystallography and chemical biology to dissect the host pathways altered by the PTPs and how the PTPs allow for better survival of MTB during infection.
The lab’s crystal structures of PtpB provide the basis for understanding substrate recognition, regulation and specificity of inhibitor binding. The inhibitor co-structure, in combination with the apo-structure of PtpB, reveals a complex sequence of folding events and a large movement of a protein segment over the active site to protect the catalytic cysteine from oxidation. The inhibitor co-structure also reveals a putative second phosphotyrosine binding site that will aid in the identification of host substrates of PtpB. Finally, the co-crystal structure provides the template for generating improved inhibitors by structure-based drug design.
The MTB cell wall is a thick and impenetrable barrier that interferes with efficient delivery of many antibacterial drugs, making novel approaches for targeting MTB necessary. Three factors make the Mtb PTPs promising drug targets: (1.) They are important for MTB survival in vivo; (2.) PTPs belong to an emerging family of druggable enzymes; and (3.) They act outside of the bacterial cell wall, and thus are more accessible to drugs than classical targets inside the bacterium. In a collaboration with the Chemistry Department at the University of California, Berkeley, the Grundner lab develops and tests the activity of PTP inhibitors against MTB.
Other pathogens that rely on tyrosine phosphorylation to control central cellular functions are Staphylococcus aureus and Trypanosoma brucei. The Grundner lab is defining the role tyrosine phosphatases and kinases play in these organisms, using methods developed for the Mtb PTPs and explores their potential as drug targets.
- MTB virulence factors
- Protein tyrosine phosphatases in microbial pathogens