SpoIVFB Site-2 protease (S2P), a zinc metalloprotease (MEROPS family M50B), regulates intramembrane proteolysis (RIP), and is involved in the pro-sigmaK pathway of bacterial spore formation. In this subgroup, SpoIVFB (sporulation protein, stage IV cell wall formation, F locus, promoter-distal B) contains two tandem repeats of the cystathionine beta-synthase (CBS pair) domain. SpoIVFB is one of 4 proteins involved in endospore formation; the others are SpoIVFA (sporulation protein, stage IV cell wall formation, F locus, promoter-proximal A), BofA (bypass-of-forespore A), and SpoIVB (sporulation protein, stage IV cell wall formation, B locus). SpoIVFB is negatively regulated by SpoIVFA and BofA and activated by SpoIVB. It is thought that SpoIVFB, SpoIVFA, and BofA are located in the mother-cell membrane that surrounds the forespore and that SpoIVB is secreted from the forespore into the space between the two where it activates SpoIVFB. It has been proposed that the CBS domain may play a regulatory role, although its exact function is unknown.
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