How integration of positive and negative regulatory signals by a STAND signaling protein depends on ATP hydrolysis

The role of nucleotide hydrolysis in signaling by signal transduction ATPases with numerous domains (STAND) is poorly understood. Here we use MaIT, the transcription activator of the Escherichia coli maltose regulon, as a model system to address this question. We have constructed the MaIT-D1 29A variant that binds ATP but does not hydrolyze it and have characterized it in vivo and in vitro. ATP hydrolysis is not essential for transcription activation but is crucial in controlling MaIT activity. MaIT cycles between an ADP-bound, resting form that is the target of negative effectors and an ATP-bound, active form, which oligomerizes. Conversion to the active form involves nucleotide exchange and depends on maltotriose binding, whereas resetting to the inactive state relies on ATP hydrolysis, which ensues MaIT multimerization. Such a controlled binary switch most likely applies to the other STAND NTPases, including Apaf-1 and the human innate immunity proteins NOD2, and CIAS1.