Structural Analysis of the Mixed Lineage Leukemia 3 (MLL3) Histone Methyltransferase Complex

Restricted (Penn State Only)
Author:
Sowers, Rosalie
Area of Honors:
Biochemistry and Molecular Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Song Tan, Thesis Supervisor
  • Teh-Hui Kao, Honors Advisor
  • Wendy Hanna-Rose , Faculty Reader
Keywords:
  • chromatin
  • nucleosome
  • x-ray crystallography
  • MLL
  • MWRA
  • histone methyltransferase
Abstract:
Chromatin enzymes are an important class of enzymes that play a key role in gene regulation by covalently modifying the nucleosome packaging unit of DNA. The mixed-lineage leukemia (MLL) protein is a histone methyltransferase enzyme that specifically methylates the lysine 4 residue of histone 3 (H3K4). MLL is important not only because of its role in transcriptional activation, but also because it is implicated in at least 10% of acute leukemias through chromosomal rearrangements (Winters and Bernt, 2017). MLL has low catalytic activity on its own and requires three cofactors WDR5, Ash2L, and RbBP5 to be fully active (Li et al., 2016). These proteins collectively make up the core MLL complex. Previous work in our lab has been hindered by instability of the MLL1 protein, and therefore I replaced MLL1 with MLL3 in the complex we use for our structural work. I have expressed and purified the MLL3 complex on the milligram scale and reconstituted it with its nucleosome substrate. This reconstituted material was used to set up crystallization trials. The goal of these trials is to produce crystals that can be used for X-ray crystallography analysis to determine the structure of the MLL/nucleosome complex, thus providing insight into its molecular mechanism and the basis for its association with leukemia.