Fall Seminar Series: Dr. Karen Allen
Boston University, Department of Chemistry
Friday, November 17, 2017 · 12 - 1 PM
Adaptation of Phosphatases as Regulators, Catalysts and Housekeepers
Abstract: In
order to identify and assess sequence markers that support structure and
specificity, we have undertaken the study of a large enzyme superfamily,
comprised mostly of phosphotransferases, the haloalkanoate dehalogenase
superfamily (HADSF). Because of the occurrence of the family in all domains of
life and the number of homologues within each organism the members provide
numerous examples of orthologues to study determinants of specificity and
paralogues to study function diversification. The HADSF has successfully
evolved several forms of chemical transformation and has experienced expansion
through substrate space. The expansion includes the invention and reinvention
(pseudoconvergent evolution) of activities within branches of the family. Notably,
members show substrate ambiguity, with activity toward a number of substrates
and significant substrate overlap between “paralogues”. Other family members
have been honed to a specific substrate with high catalytic efficiency and
proficiency. However, substrate ambiguity can also be associated with high
catalytic efficiency. In order to obtain a “panoramic view” of the superfamily,
we have employed high throughput substrate screening to a diverse set of HADSF
enzymes from a sampling of bacteria across phyla. The results highlight that
substrate ambiguity is much more prevalent than one might imagine with ~45% of
all proteins showing activity against multiple substrates. The structural basis
of promiscuity in the HADSF highlights the necessity of a binding surface with
multiple enzyme candidate residues to provide potential ligands, provided in
the HADSF by the insertion of a cap domain into the Rossmann core fold. Overall, our findings are
consistent with the concept that domain insertions act to increase the substrate
range of the superfamily.