Host-Pathogen Interactions

Dr. Cygler laboratory is interested in structural aspects of protein-protein interactions, protein complexes and protein-carbohydrate interactions. The goal is to provide  molecular basis for understanding the processes underlying bacterial infection and, in particular, the interaction between bacterial pathogens and their host, emphasizing the invasiveness and survival within host macrophages and epithelial cells. Structural biology plays an essential role in attaining this level of understanding and translating the macroscopic view of host-pathogen interactions into a three-dimensional picture of molecules in action. We apply our well established structure determination pipeline and expertise in protein-protein interactions to the investigation and characterization of intracellularly injected proteins (effectors) and their interactions with host proteins. Our methodology is ideally suited to investigate host-pathogen interactions at the molecular level. We will pursue functional roles of effectors, their interactions with host proteins and three-dimensional structures of the effectors and effector-target complexes essential for bacterial virulence. ­

The lab of Linda Chelico studies the APOBEC3 host restriction factors. These ‘host restriction factors’ are proteins expressed as part of the innate immune response and can restrict the intracellular lifecycle of viruses at specific steps. We study the capacity of the APOBEC3 enzymes to restrict the replication of HIV-1. APOBEC3 enzymes are deoxycytidine deaminases which can induce mutagenesis of HIV-1 proviral DNA through modification of cytosines to uracils in proviral DNA. Although these enzymes can be potent restriction factors, they are thwarted by the HIV-1 accessory protein Vif that induces APOBEC3 degradation through the proteasome. The goal of the Chelico lab is to achieve a biochemical and molecular understanding of APOBEC3 enzyme function and their co-evolution with HIV Vif to identify potential strategies for novel HIV therapies.

Dr. Kobryn studies bacterium Borrelia burgdorferi, the causative agent of Lyme disease in North America. Lyme disease is the most common vector-transmitted infection in North America. Untreated, Lyme disease can cause serious neurological complications and about 60% of patients develop debilitating arthritis. Additionally, among about 10% of treated patients, chronic Lyme disease symptoms can persist for months or years contributing to significant economic impacts.

The spirochetes of the genus Borrelia are unique among human bacterial pathogens in that they possess linear genomes terminated by hairpin telomeres. The telomeres of all organisms, regardless of the specific structure involved, play dual roles: the completion of DNA replication overcoming the ‘end-replication problem’ and the protection of chromosome termini from degradation and inappropriate fusions. Dr. Kobryn's research interests concern the unusual DNA hairpin telomeres of the causative agent of Lyme disease in North America: Borrelia burgdorferi. His studies have helped establish how the hairpin telomeres of this organism are formed in a site-specific telomere resolution reaction of the replicated intermediate, by an enzyme named ResT, to produce the linear daughter chromosomes. ResT uses a mechanism similar to that employed by type IB topoisomerases and tyrosine recombinases. ResT substrates are broadly similar to those of the tyrosine recombinases, enzymes that catalyze site-specific recombination events. However, ResT is unusual in that it permissively resolves substrates of many different sequences that share only certain motifs necessary for substrate recognition. Much remains to be discovered about how ResT processes so many substrates and how the DNA hairpins of the hairpin telomeres are formed during the processing reaction. An understanding of the biochemical basis of hairpin formation by ResT may lead to new Borrelia-specific therapies by inhibition or poisoning of ResT. It has become clear from the phenotype of ResT depletion in vivo and from the discovery that ResT possesses DNA annealing/unwinding activities that ResT is multifunctional.