Margy Glasner, Ph.D.
Research Summary
Understanding the co-evolution of protein structure and function is a fundamental problem in molecular biology with implications for genome annotation, protein engineering, and drug development. The canonical paradigm for protein evolution is that new functions emerge through gene duplication and divergence and that residues required for protein function are conserved, while amino acids distant from the active site are under less stringent selection and evolve more rapidly.
These processes are readily apparent in mechanistically diverse superfamilies like the enolase superfamily, in which a subset of the catalytic residues are conserved to maintain a common partial chemical reaction (stabilization of an enolate anion intermediate). On this background of common function, additional active site residues that distinguish the different families within the superfamily have divergently evolved. Each family catalyzes a very different reaction using different substrates (e.g., dehydration of acid sugars or racemization of N-succinylamino acids). Since all members of such families share a common function, we expect all members within a single family to conserve additional residues that determine substrate and reaction specificity.
The o-succinylbenzoate synthase (OSBS) family confounds this expectation. An important enzyme required for Vitamin K synthesis in >100 diverse microorganisms and plants, OSBSs can share < 15% identity, well below any reasonable threshold for assigning proteins to the same family based on sequence similarity. However, phylogenetic analysis and examination of operon context demonstrate that these proteins share both a common evolutionary origin and a common function. In addition, the only universally conserved residues in the family are also conserved in other enolase superfamily members that catalyze different reactions. In the absence of family-specific conserved residues, how has OSBS function been conserved? We hypothesize that different subfamilies employ different structural strategies for binding and orienting the substrate for catalysis. These analyses reveal at least five OSBS subfamilies, one of which is comprised of promiscuous and potentially bifunctional enzymes that also catalyze N-succinylamino acid racemization. We are identifying the specificity determinants in these subfamilies using structural comparisons as well as mutational and enzymatic analysis.
Education
Ph.D. 2003, Biology
Massachusetts Institute of Technology, Cambridge, MA
B.S. with Honors, 1995, Molecular Biology
B.M. with Honors, 1995, Music Performance
University Honors Program
University of Wyoming, Laramie, WY
Publications
BOOK CHAPTERS AND REVIEWS
Glasner ME, Gerlt JA, Babbitt PC (2007) Mechanisms of Protein Evolution and Their Application to Protein Engineering. In Advances in Enzymology and Related Areas of Molecular Biology, Volume 75: Protein Evolution. Edited by Toone EA: Wiley & Sons, pp.193-239. Glasner ME, Gerlt JA, Babbitt PC (2006) Evolution of enzyme superfamilies. Curr Opin Chem Biol 10:492-497.RESEARCH ARTICLES Rakus, JF, Fedorov AA, Fedorov EV, Glasner ME, Vick JE, Babbitt PC, Almo SC, Gerlt JA (2007) Evolution of Enzymatic Activities in the Enolase Superfamily: D-Mannonate Dehydratase from Novosphingobium aromaticivorans. Biochemistry in press. Song L, Kalyanaraman C, Fedorov AA, Fedorov EV, Glasner ME, Brown S, Imker HJ, Babbitt PC, Almo SC, Jacobson MP, Gerlt JA (2007) Prediction and assignment of function for a divergent N-succinyl amino acid racemase. Nat Chem Biol. 3, 486-91. Epub 2007 Jul 1. Glasner ME, Fayazmanesh N, Chiang RA, Sakai A, Jacobson MP, Gerlt JA, Babbitt PC (2006) Evolution of Structure and Function in the o-Succinylbenzoate Synthase/N-Acylamino Acid Racemase Family of the Enolase Superfamily. J Mol Biol 360:228-250. Giraldez AJ, Cinalli RM, Glasner ME, Enright AJ, Thomson JM, Baskerville S, Hammond SM, Bartel DP, and Schier AF (2005) MicroRNAs regulate brain morphogenesis in zebrafish. Science 308:833-838. Lim* LP, Glasner* ME, Yekta* S, Burge CB, and Bartel DP (2003) Vertebrate microRNA genes. Science 299:1540. Glasner ME, Bergman NH, and Bartel DP (2002) Metal ion requirements for structure and catalysis of an RNA ligase ribozyme. Biochemistry 41:8103-8112. Johnston WK, Unrau PJ, Lawrence MS, Glasner ME, and Bartel DP (2001) RNA-catalyzed RNA polymerization: accurate and general RNA-templated primer extension. Science 292:1319-1325. Glasner ME, Yen CC, Ekland EH, and Bartel DP (2000) Recognition of nucleoside triphosphates during RNA-catalyzed primer extension. Biochemistry 39:15556-15562. *These authors contributed equally.
