Small molecule-inducible protein oligomerization constitutes a versatile post-translational regulatory mechanism, from control of individual proteins' function and stability, to the fidelity and fates of important life processes. We here present our exciting findings on the oligomeric regulatory mechanisms of the enzyme ribonucleotide reductase (RNR) orchestrated by FDA-approved chemotherapeutics.  RNR catalyzes all four nucleoside diphosphates (NDPs) to dNDPs. As a rate-limiting enzyme in dNTP biosynthesis, RNR is an essential gene for DNA replication and repair, and a major determinant of genomic integrity. Although RNR catalytic chemistry that is hard-wired from E. coli to mammals is well-studied over the past thirty years, RNR oligomeric regulation is known to be highly divergent between bacteria and animals, presenting a unique opportunity to orthogonal anti-bacterial vs. anti-cancer drug development. We use a dual combination of small-molecule chemistry and mechanistic biology to elucidate the drug-driven pathways to RNR inhibition-coupled oligomerization. First, successful engineering of a functional hybrid RNR wherein catalytic and allosteric domains of human and E. coli RNRs are swapped, enabled a new way to interrogate ligand-promoted RNR-oligomerization (Biochemistry 2013 DOI:  10.1021/bi400781z). Second, by using transient kinetic methods, we delineate mechanistic details of individual steps dictating RNR oligomerization process. Third, we develop a platform that for the first time directly reports on small-molecule-governed RNR oligomerization, opening the doors toward discovery of potent RNR inhibitors that are oligomerization-inducers. Principles that we discover here are applicable to other regulatory proteins whose functional properties are intricately linked to protein oligomeric states.  Insights into the mechanisms of small-molecule-induced macromolecular self-assembly advance the understanding of fundamental biological processes.

Deconstructing the mechanisms of small molecule-driven protein oligomeric regulation

247th National Meeting (2014)

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