Honors Capstone Project
Date of Submission
Dr. Michael Cosgrove, Professor
Dr. Sam Chan, Professor
Arts and Science
Capstone Prize Winner
Won Capstone Funding
Sciences and Engineering
Biochemistry | Biochemistry, Biophysics, and Structural Biology
Epigenetics is the study of heritable traits that are not caused by alterations to DNA. An example of such a mechanism is histone methylation, specifically histone H3 lysine 4 (H3K4). Histones are proteins that wrap and package DNA into nucleosomes. Modifications to a histone’s chemistry can up or down regulate specific gene expression programs through changes in nucleosome positioning. Human mixed lineage leukemia protein-1 (MLL1) is a member of the SET1 family of H3K4 methyltransferases. Previous studies in the Cosgrove lab have shown that an interaction between two protein sub-complexes, MLL1 and WRAD (WDR5, RbBP5, Ash2L, DPY30), leads to dimethylation. H3K4 dimethylation plays an important role in normal development and hematopoiesis in humans. Disruption of core complex formation from amino acid point mutations can lead to a decrease, or even complete loss, of dimethylation.
Kabuki Syndrome (KS) is a multiple malformation disorder that was recently discovered to be associated with mutations in mixed lineage leukemia protein-2 (MLL2), a paralog of MLL1 and member of the SET1 family of proteins. Using the experimental model established with MLL1, tests were conducted that determined the importance of a highly conserved arginine residue (R). In MLL1, this R3765 (MLL2 R5340) was mutated into leucine, which revealed a severe loss of H3K4 dimethylation resulting from failure of MLL1 to interact with WDR5. Additional KS and non-KS (control) MLL1 mutations from MLL2 screens of patients were tested and suggested a correlation between changes in H3K4 methylation and KS.
Protein arginine deiminases (PADs) are enzymes that post translationally modify arginine into citrulline, a non-standard amino acid. Previous work with KS led us to hypothesize a possible regulation system of PAD and SET1 family proteins. While PAD is able to disrupt complex formation by changing R3765 into citrulline, thereby down-regulating dimethylation, mutations in SET1 family proteins can elevate dimethylation when in complex with WRAD. Thereby creating an “on” and “off” system of protein interaction. Previous work in the Cosgrove lab showed preferential interaction between PAD2 and MLL1. Initial assays were conducted and optimized that supported this hypothesis, as well as laying the ground work for future experimentation.
Hu, Michael, "Molecular Mechanisms for Regulating the Assembly of the Mixed Lineage Leukemia-1 (MLL1) Core Complex" (2014). Honors Capstone Projects - All. 758.
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