Evidence that SpoIVFB is a novel type of membrane metalloprotease governing intercompartmental communication during Bacillus subtilis sporulation

Processing of pro-sigma(K) in the mother cell compartment of sporulating Ba cillus subtilis involves SpoIVFB and is governed by a signal from the fores pore. SpoIVFB has an HEXXH motif characteristic of metalloproteases embedde d in one of its transmembrane segments. Several conservative single amino a cid changes in the HEXXH motif abolished function. However, changing the gl utamic acid residue to aspartic acid, or changing the isoleucine residue th at precedes the motif to proline, permitted SpoIVFB function. Only one othe r putative metalloprotease, site 2 protease has been shown to tolerate aspa rtic acid rather than glutamic acid in its HEXXH sequence. Site 2 protease and SpoIVFB share a second region of similarity with a family of putative m embrane metalloproteases. A conservative change in this region of SpoIVFB a bolished function. Interestingly, SpoIVFA increased the accumulation of cer tain mutant SpoIVFB proteins but was unnecessary for accumulation of wild-t ype SpoIVFB.