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Journal of Bacteriology, February 2005, p. 961-971, Vol. 187, No. 3
0021-9193/05/$08.00+0 doi:10.1128/JB.187.3.961-971.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
K
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan1
Received 18 August 2004/ Accepted 21 October 2004
During sporulation of Bacillus subtilis, pro-
K is activated by regulated intramembrane proteolysis (RIP) in response to a signal from the forespore. RIP of pro-
K removes its prosequence (amino acids 1 to 20), releasing
K from the outer forespore membrane into the mother cell cytoplasm, in a reaction catalyzed by SpoIVFB, a metalloprotease in the S2P family of intramembrane-cleaving proteases. The requirements for pro-
K to serve as a substrate for RIP were investigated by producing C-terminally truncated pro-
K fused at different points to the green fluorescent protein (GFP) or hexahistidine in sporulating B. subtilis or in Escherichia coli engineered to coexpress SpoIVFB. Nearly half of pro-
K (amino acids 1 to 117), including part of sigma factor region 2.4, was required for RIP of pro-
K-GFP chimeras in sporulating B. subtilis. Likewise, pro-
K-hexahistidine chimeras demonstrated that the N-terminal 117 amino acids of pro-
K are sufficient for RIP, although the N-terminal 126 amino acids, which includes all of region 2.4, allowed much better accumulation of the chimeric protein in sporulating B. subtilis and more efficient processing by SpoIVFB in E. coli. In contrast to the requirements for RIP, a much smaller N-terminal segment (amino acids 1 to 27) was sufficient for membrane localization of a pro-
K-GFP chimera. Addition or deletion of five amino acids near the N terminus allowed accurate processing of pro-
K, ruling out a mechanism in which SpoIVFB measures the distance from the N terminus to the cleavage site. A charge reversal at position 13 (substituting glutamate for lysine) reduced accumulation of pro-
K and prevented detectable RIP by SpoIVFB. These results elucidate substrate requirements for RIP of pro-
K by SpoIVFB and may have implications for substrate recognition by other S2P family members.
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