Karen Allen, PhD (Boston University)

"An Evolutionary Tale: Phosphatase Dynamics Dictate Specificity and Regulation"

When Oct 28, 2014
from 11:00 AM to 12:00 PM
Where Bioinformatics 1131
Contact Name
Attendees Open to the public
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"An Evolutionary Tale: Phosphatase Dynamics Dictate Specificity and Regulation"

Karen Allen

Professor
Department of Chemistry
Boston University

Allen Lab

Bio: Karen Allen received her BS in Biology  from Tufts University in 1984 and her PhD in Biochemistry from Brandeis University in 1989. She was an American Cancer Society Postdoctoral Fellow in X-ray Crystallography, Massachusetts Institute of Technology, 1989 and Brandeis University, 1990. Prior to joining the Department of Chemistry in 2008, she was Professor of Physiology and Biophysics at the Boston University School of Medicine. A leader in the American Chemical Society, she is currently an Associate Editor of the ACS journal, Biochemistry.

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. Notably, members show activity toward a number of substrates and significant substrate overlap between “paralogs”. Other family members have been honed to a specific substrate with high catalytic efficiency and proficiency. The construction of the family is functionally modular, with conserved chemistry provided by the Rossmann fold “core” domain and specificity provided by the accessorizing cap domain. We offer evidence, through bioinformatic analysis at the sequence and structure level, for coevolution of the cap and core domains. Moreover, the observed correlated variation is a global phenomenon with contributions from all residues of the core fold. These findings are supported by experimental thermodynamic stability studies showing cooperative unfolding of the two enzyme domains. Solution X-ray scattering studies, combined with molecular dynamics of a mutase member of the HADSF, β-phosphoglucomutase, in complex with ligands representing various substrate moieties show that occupation of the “non-transferring” phosphate-binding site is required for closure of the enzyme complex. These results show a large synergistic contribution to the conformational change between the two phosphate sites. However, covalent connection via the sugar ring has little energetic benefit indicating that substrate is not optimally aligned in the binding site. Other mutases in the family can also be regulated via dynamics and control of the catalytically competent conformation. Overall, our findings highlight the use of the cap domain structure and enzyme conformational dynamics in delineating specificity.

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