Identification of residues essential for the catalytic activity of Sec11b, one of the two type I signal peptidases of Haloferax volcanii

Sec11b is one of two signal peptidases (SPases) in the haloarchaeon Haloferax volcanii. Site-directed mutagenesis revealed Ser-72, His-137 and Asp-187 as essential for signal peptide cleavage. Thus, like the SPase of the methanoarchaeon Methanococcus voltae, H. volcanii Sec11b uses a catalytic mechanism reminiscent of its eukaryal rather than its bacterial counterpart. The availability of an additional model system to study the archaeal SPase, now in the form of the purified protein, promises additional insight into the behavior of this enzyme.