PHENOMECHANICAL · Phenotyping of protein mechanics Libraries to unravel the design principles of catch bonds

Mechanical forces that steer protein interactions and folding play pivotal roles in biology. They shape cellular fate, and are critical factors in both pathogen adhesion and immune response. Catch bonds, atypical interfaces that increase their bound lifetime under mechanical force, play a central role in these processes. At present, we have no model nor datasets large enough to predict if an interaction is a catch bond from its structure without doing experiments, let alone design new catch bonds.Single molecule force spectroscopy (SMFS) methods investigate the mechanics of proteins involved in these processes. These techniques typically have high force resolution, but extremely low throughput. An exhaustive database of proteins characterized by SMFS in the past 30 years contains only 85 entries. The overall aim of this proposal is to establish methods that allow large scale measurement of the mechanics of protein-protein interactions under force, first on hundreds, and finally on thousands of catch bonds: library-scale mechanical phenotyping. The key innovation proposed here is to link mechanostability, that is bond lifetime under an externally applied force, to a DNA-sequencing based readout by coupling phenotype to sequencing-readable genotype. Force resolution will be comparable to established flow-stretching assays, while throughput will increase by at least 2 orders of magnitude.The increased throughput will be leveraged to identify the design principles of catch bonds using de novo protein design. Ultimately, I aim to engineer new-to-nature de novo catch bonds with tunable lifetimes under force, which could find application in new biomaterials or as synthetic force-steered cell receptors. The interplay of design and high throughput testing will create large, hypothesis driven computational and experimental datasets of protein mechanics suitable to machine learning approaches, possibly opening ways to infer catch bonding behavior solely based on structure.