This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is a "MFS-family" membrane protein from E coli that stoichiometircally exchanges arginine for its decarboxylation product, agmatine. It operates as a "virtual proton pump" in the extreme acid resistance response. This protein can be easily overexpressed and crystallized, and we are currently trying to improve crystal quality to the point where we can begin serious indexing and phasing. During the past year, we have improved diffraction limit from about 20 A to 6A in the best, isotropic cases. Our trips to NSLS are used for screenng and optimization at this point. This cannot be done on our home source, as these membrane protein crystals require a high-intensity beam to assess their diffration limit. If we can achieve isotropic diffraction out to 3.5 A, we will then begin phasing, initially using MAD with SeMet derivatives, which we can readily express.