Associate Professor, CMMB and Center for Drug Discovery and Innovation (CDDI)
Office: ISA 6211 & IDRB
Lab: IDRB 1st Floor
Ph.D. University of Oregon, 1997
Research in my group is focused on identifying fundamental relationships between protein structure and function. We are particularly interested in proteins, like the tumor suppressor p53, that are involved in the development and maintenance of cancer. p53 is a tumor suppressor and cell cycle regulator that is activated by protein-protein interactions and posttranslational modifications (PTMs). Deletion or mutation of p53 can dramatically increase susceptibility to cancer. p53 is also an intrinsically disordered protein (IDP). IDPs are highly dynamic, do not form stable tertiary structures, and contain variable amounts of transient secondary structure. IDP domains are hotspots for PTMs and they frequently mediate protein-protein interactions through coupled folding and binding. IDP domains that interact with other proteins can contain defined levels of transient secondary structure that resemble their complex-bound structure. These levels of residual structure can modulate binding affinities with other proteins by tuning the change in conformational entropy that occurs during the coupled folding and binding reaction.
We are currently testing whether intrinsic levels of disorder and residual helicity within IDP domains, combined with regulation by PTMs, determine the binding affinity with protein partners and ultimately permit fine adjustments to cellular function. We have already shown that levels of residual helicity in the disordered p53 transcriptional activation domain (p53TAD) controlled the binding affinity to the E3 ubiquitin ligase Mdm2, both in vitro and inside living cells. The levels of residual helicity in free p53TAD were controlled by conserved prolines flanking the Mdm2 binding site. Mutating these prolines to alanine resulted in higher p53TAD helicity and stronger Mdm2 binding. This stronger Mdm2 binding abrogates the effects of PTMs leading to more rapid degradation of p53 following DNA damage. Lower levels of p53 reduce target gene expression and prevent cell cycle arrest. Our results suggest that precise levels of intrinsic disorder and residual helicity are necessary for regulating the p53-signaling network and changing the levels of disorder can modify the effects of phosphorylation and other PTMs. Studies from other groups have shown that PTMs can change intrinsic levels of disorder. Together levels of intrinsic disorder and PTM status allow IDP domains to dynamically respond to signaling changes in cellular networks. We are changing the levels of intrinsic disorder in p53 and determining the effects on activation dynamics and target gene expression. We are also investigating how intrinsic disorder combines with PTMs to control protein-protein interactions and how the levels of intrinsic disorder in other cancer-associated IDPs control structure and function.
If you choose to join my group, you will be exposed to the latest techniques in protein expression and purification. Protein structure and function is investigated using a variety of techniques including nuclear magnetic resonance (NMR) spectroscopy. The protein NMR facility in the Center for Drug Discovery and Innovation contains 600 and 800 MHz instruments.
Anusha Poosapati, Oluwakemi Sowemimo