Intramembrane　proteases　hydrolyze　peptide　bonds　within　the　cell　membrane　as　the　decision-making　step　of　various　signaling　pathways.　Sporulation　factor　IV　B　protease　(SpoIVB)　and　C-terminal　processing　proteases　B　(CtpB)　play　central　roles　in　cellular　differentiation　via　regulated　intramembrane　proteolysis　(RIP)　process　which　activates　pro-σK　processing　at　the　σ　K　checkpoint　during　spore　formation.　SpoIVB　joins　CtpB　in　belonging　to　the　widespread　family　of　PDZ-proteases,　but　much　remains　unclear　about　the　molecular　mechanisms　and　structure　of　SpoIVB.　In　this　study,　we　expressed　inactive　SpoIVB　(SpoIVBS378A)　fused　with　maltose　binding　protein　(MBP)-tag　and　obtained　the　solution　structure　of　SpoIVBS378A　from　its　small　angle　X-ray　scattering　(SAXS)　data.　The　fusion　protein　is　more　soluble,　stable,　and　yields　higher　expression　compared　to　SpoIVB　without　the　tag.　MBP-tag　not　only　facilitates　modeling　of　the　structure　in　the　SAXS　envelope　but　also　evaluates　reliability　of　the　model.　The　solution　structure　of　SpoIVBS378A　fits　closely　with　the　experimental　scattering　data　(χ2=　1.76).　Comparing　the　conformations　of　PDZ-proteases　indicates　that　SpoIVB　adopts　a　PDZ-protease　pattern　similar　to　the　high　temperature　requirement　A　proteases　(HtrAs)　rather　than　CtpB.　We　not　only　propose　that　SpoIVB　uses　a　more　direct　and　simple　way　to　cleave　the　substrates　than　that　of　CtpB,　but　also　that　they　work　together　as　signal　amplifiers　to　activate　downstream　proteins　in　the　RIP　pathway.　Copyright　©　2019　Xie,　Guo,　Xue,　Xie,　Yuan,　Harrison,　Li,　Jiang　and　Huang.