Evidence that the Bacillus subtilis SpoIIGA protein is a novel type of signal-transducing aspartic protease.
The bacterium Bacillus subtilis undergoes endospore formation in response to starvation. sigma factors play a key role in spatiotemporal regulation of gene expression during development. Activation of sigma factors is coordinated by signal transduction between the forespore and the mother cell. sigma(E) is produced as pro-sigma(E), which is activated in the mother cell by cleavage in response to a signal from the forespore. We report that expression of SpoIIR, a putative signaling protein normally made in the forespore, and SpoIIGA, a putative protease, is necessary and sufficient for accurate, rapid, and abundant processing of pro-sigma(E) to sigma(E) in Escherichia coli. Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of aspartic protease whose C-terminal half forms a dimer similar to the human immunodeficiency virus type 1 protease. Previous studies suggest that the N-terminal half of SpoIIGA is membrane-embedded. We found that SpoIIGA expressed in E. coli is membrane-associated and that after detergent treatment SpoIIGA was self-associated. Also, SpoIIGA interacts with SpoIIR. The results support a model in which SpoIIGA forms inactive dimers or oligomers, and interaction of SpoIIR with the N-terminal domain of SpoIIGA on one side of a membrane causes a conformational change that allows formation of active aspartic protease dimer in the C-terminal domain on the other side of the membrane, where it cleaves pro-sigma(E).
Imamura
Daisuke
D
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
Zhou
Ruanbao
R
Feig
Michael
M
Kroos
Lee
L
D016282:Aspartic Acid Endopeptidases / Q000096:biosynthesis* / Q000235:genetics; D001412:Bacillus subtilis / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D008565:Membrane Proteins; D008958:Models, Molecular; D010447:Peptide Hydrolases; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
D001426:Bacterial Proteins; D008565:Membrane Proteins; D011498:Protein Precursors; D012808:Sigma Factor; C092468:spoIIR protein, Bacillus subtilis; C063202:sporulation-specific sigma factors; D010447:Peptide Hydrolases; D016282:Aspartic Acid Endopeptidases; C071976:SpoIIGA protein, Bacillus subtilis