Structural Mechanisms and Engineering of Transmembrane Signaling

How does binding outside the cell control signaling inside the cell?

Cells receive signals outside the plasma membrane but initiate most signaling reactions inside the cell. Our laboratory studies three transmembrane receptor systems: the T cell receptor, which controls immune recognition; EGFR, which controls cell growth and survival; and integrins, which control cell adhesion, migration, and mechanical signaling.

Although these receptors have different structures, they share fundamental features. They bind extracellular ligands, change their conformation or organization in the membrane, and activate intracellular signaling pathways. Our goal is to understand these processes structurally and use this knowledge to design molecules that activate, inhibit, or redirect receptor signaling.

pMHC↓TCR–CD3↓Signal

1. Early Activation of the T Cell Receptor

T cells recognize antigens through the T cell receptor (TCR). Antigen binding occurs outside the cell, while phosphorylation of CD3 signaling motifs occurs inside the cell. The molecular connection between these events remains unclear.

Questions

  • What changes in the TCR–CD3 complex immediately after antigen binding?
  • How do membrane lipids, receptor clustering, and mechanical force affect early activation?
  • Why do some TCR antibodies activate signaling while others block it?

Approach

We reconstitute intact TCR–CD3 complexes in nanodiscs and liposomes; compare structures with peptide–MHC, antibodies, and synthetic binders; test structural interfaces by mutation; measure signaling in cells; and engineer antibody epitopes, angles, and valencies.

Goal

To identify the structural events that initiate TCR signaling and design blocking antibodies, agonists, partial agonists, and synthetic binders for controlling immune-cell responses.

7 ligands→EGFR dimer→Distinct signals

2. How Seven Ligands Produce Different EGFR Signals

EGFR is activated by EGF, transforming growth factor-α, amphiregulin, epiregulin, betacellulin, heparin-binding EGF-like growth factor, and epigen. These seven ligands bind the same receptor but can produce different signaling strength, duration, trafficking, and cellular responses.

Questions

  • Do the seven ligands produce different EGFR dimer structures?
  • How are extracellular ligand differences transmitted to intracellular kinase domains?
  • How do receptor states select downstream pathways, and why can antibodies inhibit, cluster, or partially activate EGFR?

Approach

We compare full-length EGFR complexes with each ligand in detergent, nanodiscs, and liposomes; measure receptor phosphorylation, trafficking, and RAS–MAPK, PI3K–AKT, and PLCγ signaling; and test mutations, antibodies, and binders that stabilize selected states.

Goal

To control not only whether EGFR is activated, but also how strongly, how long, and through which pathway it signals.

3. Bidirectional Signaling through Integrins

During inside-out signaling, talin and kindlin activate integrins and increase extracellular ligand affinity. During outside-in signaling, ligand binding promotes receptor clustering, cytoskeletal coupling, and intracellular signaling.

Questions

  • How do talin and kindlin activate integrins from inside the cell?
  • How does extracellular ligand binding initiate intracellular signaling?
  • Which structures correspond to inactive, intermediate, and active states?
  • How do antibodies stabilize or block particular conformations?

Approach

We reconstitute full-length integrins in defined lipid membranes; add talin, kindlin, ligands, or antibodies in controlled combinations; determine inactive and active structures; mutate transmembrane and cytoplasmic interfaces; and measure ligand binding, adhesion, spreading, and migration.

Goal

To connect adaptor binding, transmembrane rearrangement, ligand affinity, receptor clustering, and adhesion—and design blocking, activating, diagnostic, or state-selective binders.

Detergent↔Nanodisc↔Native membrane

4. Membrane Proteins in Native Lipid Environments

Detergents are useful for membrane-protein purification, but they cannot fully reproduce native membrane composition and physical properties. Lipids can directly affect receptor conformation, stability, clustering, and signaling.

Questions

  • How are receptor structures changed by native lipids?
  • Which complexes are lost during detergent purification?
  • Can liposomes or extracellular vesicles preserve native conformations?
  • Can the same membrane systems support targeted drug delivery?

Approach

We compare receptors in detergent, liposomes, nanodiscs, extracellular vesicles, and native membrane fractions; test cholesterol, phospholipids, and membrane asymmetry; visualize ligand-induced organization; and engineer targeted membrane systems.

Goal

To obtain structures closer to true cellular states and develop targeted liposomes, engineered extracellular vesicles, receptor-directed delivery systems, and membrane-displayed binders.

Structure-Guided Antibody and Binder Design

Antibodies do more than occupy receptor surfaces. Epitope, binding angle, affinity, valency, and receptor clustering can determine whether signaling is activated or inhibited. Across the TCR, EGFR, and integrin programs, we use one shared workflow:

  1. Determine receptor structures in different functional states.
  2. Identify conformational changes associated with activation or inhibition.
  3. Map antibody and ligand binding sites.
  4. Design mutations that change binding geometry or receptor state.
  5. Test signaling effects in biochemical and cellular assays.
  6. Improve antibodies and binders through repeated structure-guided engineering.

Our long-term path: structure → mechanism → molecular design → therapeutic control.