B.S., University of Pittsburgh, Biochemistry & Chemistry (2012)
Doctor of Philosophy, University of Pennsylvania (2018)
Brian Kobilka, Postdoctoral Faculty Sponsor
Membrane Proteins Have Distinct Fast Internal Motion and Residual Conformational Entropy.
Angewandte Chemie (International ed. in English)
For a variety of reasons, the internal motions of integral membrane proteins have largely eluded comprehensive experimental characterization. Here the fast side chain dynamics of the 7-transmembrane helix protein sensory rhodopsin II and the beta-barrel bacterial outer membrane channel protein W have been investigated in lipid bilayers and detergent micelles by solution NMR relaxation techniques. Though of quite different topologies, both proteins are found to have a similar and striking distribution of methyl-bearing amino acid side chain motion that is independent of membrane mimetic. The methyl-bearing side chains of both proteins are, on average, more dynamic in the ps-ns time regime than any soluble protein characterized to date. Approximately one third of methyl-bearing side chains in both proteins exhibit extreme rotameric averaging on this timescale. Accordingly, both proteins retain an extraordinary residual conformational entropy in the folded state, which provides a counterbalance to the absence of the hydrophobic effect that normally stabilizes the folded state of water-soluble proteins. Furthermore, the large reservoir of conformational entropy that is observed provides the potential to greatly influence the thermodynamics underlying a plethora of membrane protein functions including ligand binding, allostery and signaling.
View details for DOI 10.1002/anie.202003527
View details for PubMedID 32277554
Structural insights into differences in G protein activation by family A and family B GPCRs.
Science (New York, N.Y.)
2020; 369 (6503)
Family B heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) play important roles in carbohydrate metabolism. Recent structures of family B GPCR-Gs protein complexes reveal a disruption in the α-helix of transmembrane segment 6 (TM6) not observed in family A GPCRs. To investigate the functional impact of this structural difference, we compared the structure and function of the glucagon receptor (GCGR; family B) with the β2 adrenergic receptor (β2AR; family A). We determined the structure of the GCGR-Gs complex by means of cryo-electron microscopy at 3.1-angstrom resolution. This structure shows the distinct break in TM6. Guanosine triphosphate (GTP) turnover, guanosine diphosphate release, GTP binding, and G protein dissociation studies revealed much slower rates for G protein activation by the GCGR compared with the β2AR. Fluorescence and double electron-electron resonance studies suggest that this difference is due to the inability of agonist alone to induce a detectable outward movement of the cytoplasmic end of TM6.
View details for DOI 10.1126/science.aba3373
View details for PubMedID 32732395