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

Dr. James Stivers, Professor, Johns Hopkins University 

Seminar Title: “A tale of a tail: A role for disorder in DNA damage recognition”

Bio: Dr. Stivers has over 25 years of accumulated expertise in enzymology, high-throughput screening, fragment-based ligand design, cancer pharmacology and innate immunity research to guide the DNA repair studies in this proposal.  Over the years, his research program has focused on the basic science of uracil DNA glycosylase (UNG) and the uracil base excision repair pathway (UBER), fluorodeoxyuridine (floxuridine) chemotherapy and its connection with human UNG activity, antiviral/anticancer drug therapy, and the role of APOBEC DNA cytidine deaminases and SAMHD1 dNTPase in adaptive and innate immunity pathways. In particular, his lab has made unique contributions in the use of small-molecule fragment tethering to develop inhibitors of human UNG and to understand how the key dNTP regulatory protein SAMHD1 switches between its potent dNTPase activity and its DNA replication fork activity involved in nucleic acid immune sensing.  His ongoing collaborations with Pfizer-CTI have recently resulted in highly effective inhibitors of human UNG with low nanomolar activity in vitro and strong synergy with FdU in cell culture as well as a mouse xenograft model for colorectal cancer.   

Abstract: Many human DNA repair proteins have disordered domains at their N- or C-termini with poorly defined biological functions. We recently reported that the partially structured N-terminal domain (NTD) of human uracil DNA glycosylase 2 (hUNG2), functions to enhance DNA translocation in crowded environments and also targets the enzyme to single-stranded/double-stranded DNA junctions. To understand the structural basis for these effects, we now report high-resolution heteronuclear NMR studies of the isolated NTD in the presence and absence of an inert macromolecular crowding agent (PEG8K). Compared to dilute buffer, we find that crowding reduces the degrees of freedom for the structural ensemble, increases the order of a PCNA binding motif and dramatically promotes binding of the NTD for DNA through a conformational selection mechanism. These findings shed new light on the function of this disordered domain in the context of the crowded nuclear environment. 

Dr. Li Fan, li.fan@ucr.edu