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The focal adhesion kinase (FAK) scaffold provides FAK-targeted cancer therapeutics with greater efficacy and specificity than traditional kinase inhibitors. The FAK scaffold function largely involves the interaction between FAK’s focal adhesion targeting (FAT) domain and paxillin, ultimately regulating many hallmarks of cancer. We report the design of paxillin LD-motif mimetics that successfully inhibit the FAT-paxillin interaction. Chemical and biochemical screening identifies stapled peptide 1907, a high affinity binder of the FAT four-helix bundle with ~100-fold greater binding affinity than the native LD2-sequence. The X-ray co-crystal structure of the FAT-1907 complex is solved. Myristoylated 1907-analog, peptide 2012, delocalizes FAK from focal adhesions, induces cancer cell apoptosis, reduces in vitro viability and invasion, and decreases tumor burden in B16F10 melanoma female mice. Enzymatic FAK inhibition produces no comparable effects. Herein, we describe a biologically potent therapeutic strategy to target the FAK-paxillin complex, a previously deemed undruggable protein-protein interaction. 

Abstract Serial femtosecond crystallography (SFX) with X-ray free electron lasers (XFELs) allows structure determination of membrane proteins and time-resolved crystallography. Common liquid sample delivery continuously jets the protein crystal suspension into the path of the XFEL, wasting a vast amount of sample due to the pulsed nature of all current XFEL sources. The European XFEL (EuXFEL) delivers femtosecond (fs) X-ray pulses in trains spaced 100 ms apart whereas pulses within trains are currently separated by 889 ns. Therefore, continuous sample delivery via fast jets wastes >99% of sample. Here, we introduce a microfluidic device delivering crystal laden droplets segmented with an immiscible oil reducing sample waste and demonstrate droplet injection at the EuXFEL compatible with high pressure liquid delivery of an SFX experiment. While achieving ~60% reduction in sample waste, we determine the structure of the enzyme 3-deoxy-D-manno-octulosonate-8-phosphate synthase from microcrystals delivered in droplets revealing distinct structural features not previously reported.