CryoSHIELDs: tunable amphipathic peptide additives for cryo-EM
While cryogenic electron microscopy (cryo-EM) has transformed structural biology, sample preparation remains a major determinant of success. Specifically, the air-water interface (AWI) can damage complexes, impose preferred orientation, and reduce particle density. Here, we introduce cryoSHIELDs, a chemically diverse library of peptide additives designed to passivate the AWI and improve cryo-EM grid preparation. Across 24 protein systems spanning GPCRs, ABC and SLC transporters, soluble and Fab-containing complexes, and enzymes, cryoSHIELDs increased the success rate of structure determination. Individual cryoSHIELDs improved particle density, angular sampling, complex stability, and, for routine targets, map quality and resolution. This toolkit enabled the structural characterization of important targets, including the ABCC6 transporter, revealing unique TMD0-mediated stabilization, and DAMGO-bound -opioid receptor-Gi complex using substantially lower protein concentration. CryoSHIELDs provide a simple, tunable, and broadly applicable platform for more reliable cryo-EM in discovery biology and structure-based drug development.