Characterization of the yaeL gene product and its S2P-protease motifs in Escherichia coli.

An Escherichia coli open reading frame, yaeL, encodes a predicted homolog of human site-2 protease (S2P), a putative membrane-bound zinc metalloproteinase involved in the proteolytic activation of regulatory factors for sterol biosynthesis and for stress responses. The potential importance of YaeL in processes analogous to the regulated intramembrane proteolysis in E. coli prompted us to characterize it. Cell fractionation and alkaline phosphatase fusion experiments established that YaeL has four transmembrane segments with both termini orienting toward the periplasm. A strain in which a chromosomal disruption of yaeL was combined with arabinose promoter-controlled yaeL on a plasmid enabled us to deplete this protein from the cell. The depletion was found to cause rapid loss of viability, cell elongation and growth cessation. Mutations affecting the HEXXH metalloproteinase motif and those affecting the LDG motif, conserved among S2Ps, abolished the ability of YaeL to support cell growth. These results indicate that YaeL is indispensable in E. coli, and probably functions as a metalloproteinase at the membrane.