Allison Kumar:
Title: The secret(ion) is out: The serine tail of PrsA2 is critical for client protein interactions
Abstract:
Listeria monocytogenes (Lm) is a Gram-positive bacterium that can survive in the environment as a saprophyte yet can cause serious life-threatening infections once ingested by a susceptible mammalian host. The switch from life outside in the environment to inside a host requires the transcriptional activator PrfA, a master regulator of bacterial virulence. Within the host, PrfA exists in a high activity state and regulates the expression of secreted virulence factors including the pore forming toxin, listeriolysin O (LLO), necessary for host cell invasion. The activity of several of these secreted virulence factors is dependent on the secreted peptidyl-prolyl isomerase (PPIase) chaperone, PrsA2. The PrsA2 PPIase and foldase domains were defined and characterized for ΔprsA2-associated phenotypes, including reduced virulence and motility. However, a PrsA2 region that remains uncharacterized is the intrinsically disordered C-terminal serine-rich tail. We hypothesize that the PrsA2 serine-tail is critical for client protein interactions. Therefore, we generated Lm prsA2 serine-tail deletion and serine-to-alanine substitution strains and characterized these mutants for ΔprsA2-dependent phenotypes. We determined that the prsA2 serine-tail is critical for functional secreted hemolytic activity and is required for mouse virulence. Then, to probe the direct interaction of PrsA2 with LLO, we used a biophysical assay, isothermal titration calorimetry, which suggests that the PrsA2 serine-tail deletion mutant interacts with LLO at lower affinity than wild-type PrsA2. In addition, using a chaperone-assisted folding assay, we demonstrate that the PrsA2 serine-tail is critical for folding LLO. This study suggests that the PrsA2 serine-tail is required for the full functional activity of LLO, and we anticipate that it is important for interaction with additional key virulence factors.
Cahoon Lab
Sanjana Parimi:
Title: Intrinsically Disordered Regions in LARP1 Enable Different Interactions in its La-mod Domain
Abstract:
In a cell, mRNAs are decoded for protein synthesis through a process called translation. RNA binding proteins (RBPs) ensure mRNA metabolism matches the needs of the cell, in part by managing successful and efficient translation. One superfamily of RBPs is the La-related proteins (LARPs). While all LARPs are characterized by a region called the La-module, each of the seven LARP subfamilies has a unique function.
The LARP1 La-module consists of a La motif, a linker, and a predicted RNA recognition motif (RRM)-like region, which work synergistically to bind RNAs. While the La-motif is structured, both the linker and the formerly proposed RRM are now believed to be intrinsically disordered regions (IDR). Since IDRs have neither regular secondary structures, nor corresponding tertiary structures, they impart dynamic flexibility to a protein. As disorder itself can be functional, IDRs challenge the classical “protein structure determines function” saying. Despite their prevalence in proteins, IDRs and their structural dynamics are not well characterized.
The LARP1 La-module associates with several binding partners, including pyrimidine-rich mRNA 5’UTRs, poly(A) RNA, and Poly(A) Binding Protein (PABP). It is important to elucidate the structural changes that facilitate and result from these binding events, as they provide insight into how LARP1 executes its biological functions. I hypothesize that the LARP1 La-module equilibrates among many conformations that allow its IDR to interact with different targets, and in some cases, become more ordered into different sets of structures. To test this, we will be using biochemical, structural, and computational tools.
Berman Lab
Friday, September 15th, 2023
12:00PM
Langley A219B