Stephen C. HarrisonDepartment of Biological Chemistry and Molecular Pharmacology
Harvard Medical School
Seeley G. Mudd Building, Room 130
250 Longwood Avenue, Boston, MA 02115
tel: (617) 432-5609; fax: (617) 432-5600
Howard Hughes Medical Institute Laboratory of Molecular Medicine
The overall objective of our research is to understand how protein interactions determine subcellular structure. We use direct structural approaches - principally X-ray crystallography, often in combination with electron microscopy, - to determine the atomic organization of macromolecular complexes. Our present work tackles three broad questions about molecular localization in cells: (1) How do protein assemblies that control transcription integrate diverse signals in switching on or off the expression of specific genes?; (2) How do proteins that control transcription recognize, both individually and in combination, their DNA binding sites?; and (3) What is the nature of the molecular machinery for various transport steps in membrane traffic? Our Howard Hughes Medical Institute laboratory is at two locations - the Seeley Mudd Building and the Enders Building at Boston Children's Hospital.
Structural studies of viruses have contributed significantly over the years to understanding the principles of protein assembly, as well as to elucidating the molecular basis of viral pathogenesis. Recent work in structural virology in our laboratory includes studies of reo- and rotaviruses, of polyoma and papillomaviruses and flavivirus envelope proteins. We are also analyzing receptor-binding and fusion activities of the HIV-1 envelope glycoprotein. A recently determined structure of L1 protein from human papillomavirus shows important parallels with polyomavirus VP1 and a striking concentration of variability in the outward-facing surface loops.
Crystallographic analysis of the reovirus core, a particle approximately 700A in diameter, has revealed the working of an elegant molecular machine that exports mRNA and modifies its 5' end. We are following that effort with structural analyses of the reo- and rotavirus proteins that mediate the receptor binding and penetration. The reovirus penetration protein is proving to be a particularly suitable target for dissecting the mechanism of membrane perforation that must accompany viral entry.
Protein assemblies act as integrators for the many inputs that converge on the decision to activate (or repress) transcription from a given promoter. The interaction of multiple transcription factors with a composite site in a promoter or enhancer in effect "encodes" this integration in the interfaces between participating proteins. The crystal structure of a complex of the nuclear factor of activated T-cells (NF-AT), Fos and Jun on a DNA site from the IL-2 promoter has given us an informative view of one assembly of this kind. Longer-range goals include even more elaborate assemblies.
The molecular machinery that carries out vesicular transport I in eukaryotic cells includes components (e.g., clathrin, in one of the important transport pathways) that help drive vesiculation, as well as components that determine specific incorporation of protein cargo (e.g., adaptor complexes). We have begun to analyze the structures of these proteins and the specificity of their interactions, in collaboration with Tomas Kirchhausen. We have also initiated a collaborative effort with Tom Rapoport to study the structural basis of protein translocation across membranes.
Chen, L., Glover, J.N.M., Hogan, Patrick G., Rao, A., Harrison, S.C. "Structure of the DNA Binding Domains from NFAT, Fos and Jun Bound Specifically to DNA", Nature 392, 42-48 (1998).
Huang, H., Chopra, R., Verdine, G.L., and Harrison, S.C. "Structure of a Covalently-Trapped Catalytic Complex of HIV-1 Reverse Transcriptase: Implications for Nucleoside Analog Drug Resistance." Science, 282, 1669-1675 (1998).
Musacchio, A., Smith, C.J., Roseman, A.M., Harrison, S.C., Kirchhausen, T., Pearse, B.M.F. "Functional Organization of Clathrin Coats: Combining Cryo-Electron Microscopy and X-ray Crystallography. Molecular Cell 3: 761-770 (1999).
Lei, M., Lu, W., Meng, W., Parrini, M-C., Eck, M.J., Mayer, B.J., Harrison, S.C. "Structure of PAK1 in an Autoinhibited Conformation Reveals a Multistage Activation Switch." Cell 102: 387-397 (2000).
Reinisch, K.M., Nibert, M., Harrison, S.C. "The Reovirus Core: Structure of a complex molecular machine." Nature 404: 960-967 (2000).
Liemann, S., Chandran, K., Baker, T.S., Nibert, M., Harrison, S.C., "Structure of the reovirus membrane-penetration protein, m1, in a complex with its protector protein, s3". Cell 108: 283-295 (2002).
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