Kathryn M. Ferguson, PhD

We are interested in extracellular control of receptor tyrosine kinases (RTKs) in both normal and neoplastic environments. The 58 RTKs in the human proteome fall into 20 classes based on the domains of their extracellular regions (ECRs). Ligand-induced dimerization is a central component in the activation of most RTKs, but it is increasingly clear that there is great diversity in the mechanisms of regulation of receptor activation across the RTK superfamily. RTKs can be subject to complex allosteric regulation by their ligands, by co-receptors and by other modulators. We seek molecular understanding of these diverse mechanisms, and of how receptor activity can be modulated by disease linked mutations or regulated by therapeutic agents. We apply a combination of biophysical, structural, biochemical and cellular approaches.

Mechanisms of activation of RTKs that are dimeric in the unliganded state:

For most (if not all) RTKs, regulation involves more than simple ligand-induced dimerization. In some cases, RTKs form dimers in the absence of ligand so activation must proceed by some alternate mechanism. The insulin receptor (IR), for example, is a disulfide-bonded dimer that is regulated by ligand induced conformational changes. We are interested in the regulation of RTKs that form non-covalent inactive dimers, such at Tie2, that forms an unliganded dimer mediated by its membrane proximal FNIII domains, and the invertebrate epidermal growth factor receptors (EGFRs) that form dimers of varying stability and poorly characterized structure. How ligand induces activation in these cases is not well understood and may involve conformational rearrangement in a dimer or formation of higher order oligomers (or both). We are using cryo-electron microscopy to gain structural insights into the ligand induced changes for these dimeric RTKs, and test our structure derived mechanistic hypotheses with biochemical, cellular and in vivo assays.

Understanding how the membrane environment directs RTK structure and function:

As part of a new NIH-funded interdisciplinary team science program, we and several other laboratories in the Departments of Pharmacology and Cell Biology are working to understand how membrane composition directs membrane protein structure and function. We seek to define the components (lipid & protein) of functional complexes isolated from native membranes, to study the role of the local membrane environment in the function and regulation of the integral membrane proteins, and to determine the 3-dimensional structures of functional complexes. Members of the team focus on different biological systems exploiting their complementary expertise in cryo-electron microscopy, mass spectrometry, multi-omic analysis, optical imaging, biochemistry and cellular signaling. In the Ferguson group, we focus on select RTKs where modulation of function by lipid components is well characterized, and the potential to alter receptor function with drugs that modulate the local membrane environment has been suggested.

Antibody modulation of RTK regulation

Our laboratory has a long-standing interest in the mechanisms of inhibition of receptor tyrosine kinases (RTKs) by therapeutic antibodies, most notably those that bind the epidermal growth factor receptor (EGFR) - one of the first targets of antibody-based drugs to treat cancer. Most therapeutic antibodies to EGFR family members were developed before there was any structural understanding of the activation mechanism of these receptors. Whereas most therapeutic EGFR antibodies block ligand binding, inhibition of EGFR activity contributes little to the clinical effects. We seek to understand how select existing antibodies may alter receptor conformation to modulate function and whether somatic mutations in EGFR receptors may alter antibody binding. We are also developing new mechanism-based antibody therapeutics, drawing on the rich understanding of EGFR family receptor structure and dynamics. We combine X-ray crystallography, cryoEM, biochemistry, computational analysis, and cellular studies to address these questions.