3s99 is a 1 chain structure with sequence from Brucella abortus 2308. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
PBP_BRUA2 Binds adenine and probably also other purines, such as guanine. May play a role in adenine and guanine uptake. May be part of an ABC-type uptake system for adenine and similar ligands (By similarity).