The Laboratory of Structural Cell Biology

Research

Icosahedral assembly of L1 protein from human papillomavirus 16

The long-term objective of our research is to determine how protein interactions determine subcellular structures. One component of our work concerns the structure, assembly, and cell-entry properties of virus particles; a second, the structural basis for integration of diverse molecular signals, both in transmission of information from the cell membrane to the nucleus and in regulating gene expression; a third, the molecular machinery for various transport steps in membrane traffic; a fourth, the molecular organization of kinetochores.

Structural studies of viruses have contributed significantly 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, with an emphasis on mechanisms of membrane penetration by these non-enveloped particles, and studies of flavivirus envelope proteins. We are also analyzing receptor-binding and fusion activities of the HIV envelope glycoprotein. (Our work in structural virology includes collaborations with Max Nibert, HMS; Philip Dormitzer, Children's Hospital; Richard Bellamy, University of Aukland, NZ; scientists at Hawaii Biotech, Aiea, HI).

Protein assemblies act as integrators for the many inputs that converge on the decision to active (or repress) transcription from a given promoter. The interaction of multiple transcription factors with a composite site in a promoter or enhancer "encodes" this integration in the interfaces between participating proteins.

Reovirus core

To determine structures that actually carry out this integration, we are investigating the components (transcription factors, co-activators, and so forth) that form the b-interferon enhanceosome. Our goal is to visualize directly how they assemble into a large, protein-DNA complex. (Collaboration with Tom Maniatis, Harvard Dept. of Molecular and Cellular Biology.)

The molecular machinery that carries out vesicular transport 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 (CBR). Some of our most exciting recent progress includes use of electron cryomicroscopy to study clathrin assemblies, in collaboration with Thomas Walz (HMS) and Niko Grigorieff (Brandeis University). We are also engaged in a collaboration with Tom Rapoport (HMS) to study the structural basis of protein translocation across membranes.

A recently initiated, long-term project in our laboratory is an effort to work out the molecular organization of a kinetochore, the assembly that links the centromeric DNA of a chromosome to the microtubules of the mitotic spindle. The yeast kinetochore, as analyzed by our collaborator (Peter Sorger, MIT), is an assembly of defined subcomplexes. We plan to use x-ray crystallography and electron microscopy to determine three-dimensional structures for these subcomplexes and ultimately to reconstruct how they form a functional kinetochore.