Northwestern University Feinberg School of Medicine

Kathleen Green Lab

What We Do in the Green Lab: From Molecules to Man

Within multicellular organisms, cells depend on the proper synthesis and folding of individual molecular building blocks, assembly of these into larger structures and the proper deployment and functioning to maintain tissue homeostasis.  In the Green lab we study all of these levels of cell biology, from molecule to man.  We are trying to understand the nature of the machinery that holds cells together, allowing them to mechanically and chemically communicate, and why this machinery is critical for human health.

This figure illustrates the organizational levels of biology, from gross anatomic to atomic levels of resolution:  Starting with a human hand from a patient with SPPK, we can analyze the tissue at the cellular, subcellular, molecular and sub-molecular (atomic levels).  We can also assess how human mutations alter protein dynamics in cells, and through all of these approaches better understand the underlying molecular basis for the disease, and how to treat it.

The upper left panel shows the hand from a patient with Striate Palmar Plantar Keratoderma (SPPK), the first reported disease caused by mutations in desmoplakin (DK Armstrong et al. 1999. Hum. Mol. Genet. 8:143). To the right, the next panel is an immunofluorescence micrograph of epidermal cells stained for desmosomes (green), keratin intermediate filaments (red) and nuclei (blue), where we can visualize the localization of both wild type and mutant proteins and their effect on this supracellular scaffold that links all cells in the epithelial sheet. Next, an electron micrograph of a desmosome shows the organelle’s structure with a dense mat of intermediate filaments closely associated on either side of the two highly specialized plasma membranes. Rotary shadowing in the bottom image, courtesy of Ed O’Keefe (EJ O’Keefe, et al. 1989. J. Biol. Chem. 264:8310) illustrates our ability to look at the structure of proteins in vitro, such as that of the desmoplakin homodimer shown here depicted as a dumbbell shaped protein with an alpha-helical coiled-coil central domain are flanked by globular N and C termini. In the final image the X-ray crystal structure of the individual protein is used to elucidate the amino acid interactions of each molecule, shown here is a single plakin repeat domain from the C-terminal IF binding domain of desmoplakin with each of the 38 residue plakin repeats labeled (R1-R5), courtesy of W. Weis (Choi, et al. Nat. Struct. Biol. 9:612).