Project Summary Supplement funds are requested under PA-18-591 and NOT-GM-20-013 to purchase a BD FACS Melody cell sorting instrument. The system will support NIGMS award R35GM118166. Research in this award emphasizes the interface between structural biology, molecular biophysics, and immunology. Broadly speaking, work in this project strives to connect the fundamental biophysical principles that govern protein behavior with molecular recognition in the immune system. This work is also instructional for understanding the basic rules of molecular recognition and elucidating principles for protein modeling and design in complex systems. Major amounts of work in the project now relies on library screening. This is used to identify mutations which govern specificity, to understand how specificity and affinity can be altered, and to identify which targets are recognized and which are not. The screening processes rely on fluorescent activated cell sorting. Technology currently available to the laboratory is aging, unnecessarily complex, requires advance scheduling, and necessitates paying expensive user fees. The streamlined, single laboratory system requested here will permit more a rapid advance towards the project goals. 85% of the system cost is requested from NIGMS. The remaining 15% will be contributed by the University of Notre Dame.