Jennifer Ekstrom Research Interests
The Ekstrom lab uses X-ray crystallography to study the three-dimensional
structures of biologically and medically important proteins. Currently, our focus is on proteins and protein complexes involved in transcriptional regulation, but we are also studying select
enzymes with interesting functional properties and potential for drug design.
In collaboration with Arul Chinnaiyan (U Mich), we are structurally characterizing the multiprotein regulatory complexes formed from the polycomb-group (PcG) family of proteins.
Polycomb-group complexes are involved in chromatin modification and in the stable repression of specific sets of genes; this repression plays a critical role in embryonic development and in maintaining the identity of differentiated cells during cell division.
The PcG protein EZH2 is upregulated in metastatic cancer, with higher concentrations of EZH2 correlating with worse prognoses, and lowered concentrations inhibiting cell proliferation in vitro.Increased EZH2 expression results in the repression of 163 different genes, including key transcription factors and cell-cycle regulators. Blocking EZH2 expression using RNA interference arrests cell growth. Therefore, EZH2 is an appealing target for novel “transcription-based” cancer therapies.
EZH2 interacts with its partner protein, EED, forming a chromatin-bound PcG complex. The PcG complex modifies the histone tails of chromatin; EZH2 methylates the N-terminal tail of histone H3, while a histone deacetylase (HDAC) associated with EED acetylates the histone H3 tail. EZH2 has no detectable homolog in the PDB by BLAST, PSI-BLAST or consensus fold-recognition servers. Mapping studies have allowed us to focus on the regions involved in the EZH2/EED intermolecular interactions and select useful constructs for crystallization.
Disulfide shuffling & chaperone activity - Protein Disulfide Isomerase
The formation of native disulfide bonds is essential for the folding and stability of many secreted proteins. Protein disulfide isomerase (PDI) is a complex multi-domain enzyme that catalyzes both the formation of disulfide bonds and the re-shuffling of existing disulfide bonds. PDI has an unusually reactive cysteine (pKa 4) that attacks the exposed disulfides of a misfolded protein; the resulting mixed disulfide may then be reshuffled to form a different disulfide bond. Native disulfide bonds are less likely to be attacked by PDI, since they are often buried in stable tertiary structure and, thus, not as easily exposed for attack.
PDI also acts as a general chaperone, binding to misfolded or poorly soluble proteins, even those without disulfide bonds. PDI is found as an integral subunit of several protein complexes such as prolyl-4-hydroxylase and the microsomal triglyceride transferase complex, effectively acting as a “permanent” chaperone for these poorly soluble proteins.
We are determining structures of mammalian PDI with a variety of peptide substrates. Our goal is an understanding how this enzyme binds to unfolded or misfolded proteins and how it catalyzes disulfide formation and exchange in target proteins.