The Department of Biochemistry's weekly BCH 252 seminar series is presented this week by:

Hiwot Anteneh, PhD Candidate, BCMB Graduate Program, UC Riverside 

Seminar Title: "DNA methylation in health and disease"

Abstract: DNA methyltransferase DNMT3A is essential for establishment of mammalian DNA methylation during development. The R882H DNMT3A is a hotspot mutation in acute myeloid leukemia (AML) causing aberrant DNA methylation. However, how this mutation affects the structure and function of DNMT3A remains unclear. Here we report structural characterization of wild-type and R882H-mutated DNMT3A in complex with DNA substrates with different sequence contexts. A loop from the target recognition domain (TRD loop) recognizes the CpG dinucleotides in a +1 flanking site-dependent manner. The R882H mutation reduces the DNA binding at the homodimeric interface, as well as the molecular link between the homodimeric interface and TRD loop, leading to enhanced dynamics of TRD loop. Consistently, in vitro methylation analyses indicate that the R882H mutation compromises the enzymatic activity, CpG specificity and flanking sequence preference of DNMT3A. Together, this study uncovers multiple defects of DNMT3A caused by the R882H mutation in AML.

Deep enzymology studies as well as whole genome bisulfite sequencing of human embryonic stem cells reveal a novel flanking sequence preference of DNMT1. To understand the mechanism behind the flanking sequence preference, structures of mDNMT1-prefereed DNA complexes (CCG and ACG-motifs) were solved and compared with a previously solved structure harboring a disfavored substrate with a central hemimethylated GCG-motif (PDB 4DA4). Marked conformational differences in DNA topology at the central hemi-mCpG site and in the catalytic helix of mDNMT1 were observed between the favored and the disfavored substrate containing complexes. These structural and biochemical observations will lead to a better understanding of how CpG-flanking sequences play part in shaping DNMT1-mediated genomic methylation patterns.

Faculty Host: Ernest Martinez; ernest.martinez@ucr.edu