We study the response of proteins found on the surface of cell membranes to various binding constitutions and the related cellular response to the binding.
We propose that cellular responses to stimuli in health and disease can be understood and predicted based on quantitative knowledge of interaction strengths between proteins involved in signaling. Towards this goal, we have developed experimental methods that yield a quantitative description of lateral interactions and activation of receptor tyrosine kinases (RTKs) in cellular membranes.
RTKs play key roles in cell growth, differentiation, metabolism, and migration. Enhanced dimerization leads to persistent autocrine activation and tumorigenesis, or impaired growth. Some RTK mutations are expected to induce pathologies by stabilizing the active dimeric state. Examples are the Ala391Glu mutation in human fibroblast growth factor receptor 3 (FGFR3), linked to Crouzon syndrome with acanthosis nigricans, and the oncogenic Val664Glu mutation in rat Neu. Both mutations occur in the transmembrane (TM) domains of the receptors and are believed to mediate stabilizing hydrogen bonding interactions within the membrane.
To address quantitatively the effect of the mutations on receptor activation, we have measured the fraction of activated Neu receptors (both the wild-type and the Val664Glu mutant), as well as the fraction of activated chimeric Neu receptors with the TM domain substituted with FGFR3 TM domain (both the wild-type and Ala391Glu mutant).
The experimental data are well-described by theoretical predictions describing a simple equilibrium between inactive monomers and active dimers. The increase in activation propensities due to the Neu Val664Glu mutation and the FGFR3 Ala391Glu mutation were measured as -1.0 kcal/mole and -0.6 kcal/mole, respectively. These results are similar to FRET-based measurements for the isolated TM domains in model lipid systems. Thus, the same physical-chemical interactions stabilize the pathogenic mutants in model systems and in cells, and a common physical basis may underlie diverse RTK-mediated human pathologies.