MIT Chemistry Directory

Mei Hong

Professor

Our laboratory focuses on the development and application of solid-state NMR spectroscopy to elucidate the structure and dynamics of biological macromolecules, especially membrane proteins. Our research spans fundamental spectroscopy and applications to biology, pharmacology, and biomaterials. We have a long-term interest in ion channels and curvature-inducing membrane proteins. We are also interested in biological complexes such as polysaccharides and glycoproteins of plant cell walls. Magic-angle-spinning (MAS) solid-state NMR spectroscopy is our principal tool for these biophysical studies, because it provides atomic-resolution structural and dynamical information on noncrystalline and insoluble macromolecules in their native environments.

Influenza M2 proteins
Ion channels and transporters provide conduits for the passage of ions and polar compounds across the hydrophobic barrier of lipid membranes. The influenza M2 protein is a multifunctional protein with proton-channel activity as well as membrane scission activity; the former is important for virus entry while the latter is required for virus budding. M2 of influenza A viruses (AM2) is also the target of one of two classes of antiviral drugs against flu. We have been investigating the proton-conduction mechanism, drug-inhibition mechanism, and curvature-inducing mechanism of M2 using solid-state NMR. A wide range of NMR techniques for measuring distances, conformation, membrane-bound orientation, and motional geometry is developed and applied. Our results on the transmembrane domain of AM2 have revealed the drug-binding site, the dynamic structure of the proton-selective histidine and channel-gating tryptophan, and the lipid interactions of an amphipathic helix that causes membrane curvature. How the ectodomain and the cytoplasmic domain modulate the proton-channel activity and mediate the virus-budding function is being investigated through structure determination of the full-length protein. With our collaborators we are also studying new drugs that target mutant M2 proteins that are resistant to the current family of amantadine drugs.

Viral fusion proteins
Many membrane proteins cause membrane curvature for function. An example is the family of viral fusion proteins, which merge the virus envelope and the target-cell membrane during virus entry into cells. Existing models of viral fusion postulate specific oligomeric structures and lipid interactions of two hydrophobic domains in these proteins: the fusion peptide domain and the transmembrane domain. Using solid-state NMR spectroscopy, we are probing the conformation, oligomeric structure and lipid- and water-interactions of these two domains of parainfluenza and related viruses, to understand how these hydrophobic domains perturb the lipid bilayer and reduce the hydration pressure to achieve fusion.

Cationic membrane peptides
Although the interior of lipid membranes is highly hydrophobic, a surprising number of cationic membrane-active peptides exist in biology. Examples are antimicrobial peptides produced by animals and plants for immune defense against microbes, cell-penetrating peptides that act as the Trojan horse of macromolecular cargos into cells, and voltage-sensing domains of ion channels. All these membrane peptides and protein domains contain many arginine and lysine residues, whose transport from aqueous solution to lipid bilayers presumably encounters a large free-energy barrier. We are interested in the structure, dynamics and lipid interactions of these membrane peptides, to understand the mechanism with which these cationic molecules overcome the free-energy barrier to insert into the lipid membrane.  31P, 13C and 2H solid-state NMR experiments are used to measure the membrane morphology and domain structure induced by these peptides, the peptide structure and dynamics, and the interactions among the cationic residues, lipid and water.

Plant cell walls
The polysaccharides and glycoproteins of plant cell walls form functional but still poorly understood three-dimensional structures. We have pioneered the first 2D and 3D MAS correlation solid-state NMR studies of the primary cell walls of the model plants Arabidopsis thaliana and Brachypodium distachyon. These multidimensional NMR studies are made possible by isotopic enrichment of whole plants and by the use of the sensitivity-enhancing dynamic nuclear polarization technique developed by Griffin and coworkers. Our results reveal, for example, that cellulose, hemicellulose and pectins form a single spatial network, which revises the long-held “tethered network” model of the primary cell wall. With our collaborators, we are investigating how proteins bind to polysaccharides to achieve their functions, the detailed conformation of key polysaccharides in intact plants, hydration of wall polysaccharides, and pectin-cellulose and hemicellulose-cellulose interactions. Intermolecular correlation, spin diffusion, and dynamics NMR techniques are developed and applied for these studies.

Solid-state NMR techniques for biomolecular structure determination
We continue to expand the capability of solid-state NMR spectroscopy to address cutting-edge biological questions. Some of our long-standing interest are: multinuclear distance-measuring techniques (e.g. 19F-19F, 13C-2H, 13C-31P and 13C-1H distances); intermolecular correlation experiments that probe protein-lipid, protein-water and polysaccharide-water interactions; 2D and 3D correlation techniques and computational methods for resonance assignment of NMR spectra; anisotropic-isotropic correlation techniques to measure torsion angles and molecular motion; and isotopic labeling strategies for proteins and other biological molecules.
 

Contact Information

t: 6172535521
e: MEIHONG@MIT.EDU

Office

NW14-3212

Education

B.A. 1992, MOUNT HOLYOKE COLLEGE
Ph.D. 1996, UNIVERSITY OF CALIFORNIA-BERKELEY

Administrative Assistant

Jillian Haggerty

Email:jhaggert@mit.edu
Tel: (617) 253-5478
Room NW14-3218
77 Massachusetts Ave.
Cambridge, MA 02139