Karen Allen, PhD
Professor, Department of Chemistry, Boston University
Associate Professor, Physiology & Biophysics, Boston University School of Medicine

Host: Jiaoyang Jiang

Form Follows Function:  Evolution of Protein Scaffolds for Phosphoryl Group Transfer

In order to identify and assess sequence markers that support structure and specificity, we have undertaken the study of two enzyme superfamilies, comprising phosphotransferases and phosphoglycosyltransferases, the haloalkanoate dehalogenase superfamily (HADSF) and the phosphoglycosyl transferase superfamily (PGT). Both families enact chemistry on phosphorus through covalent phosphoaspartyl intermediates, however the PGTs have the additional challenge of utilizing membrane-bound substrates. Most HADSF members, including βPGM, consist of a catalytic core Rossmann fold and cap domain insert that folds over the substrate upon binding. β-phosphoglucomutase (βPGM), is used as a model to show how in the mutases of the family, interdomain conformational changes are coupled to ligand binding and govern the switch between mutase and phosphatase activity. Furthermore, we show that human phosphomannomutase can be “allosterically” regulated via dynamics and control of the catalytically competent conformation. In the PGT family, our study reveals the first structure of a PGT superfamily member, C. concisus PglC, revealing a novel protein fold with an unusual re-entrant membrane helix which comprises part of the protein fold rather than adopting a membrane spanning topology. Additionally, key structural motifs establish the co-facial positioning of the catalytic-dyad Asp/Glu and reveals how the alpha-helix associated beta-hairpin (AHABh) motif characteristic of this novel fold acts to activate the carboxylate nucleophile. Overall, the structure of PglC enforces placement of the active site at the membrane interface which is energetically favorable for use of a undecaprenyl phosphate substrate.