PMC

Proposed subcellular localization, topology, and function of StoA in the intermembrane space of a forespore engulfed by the mother cell. The sporulation protein(s) (X) that requires disulfide bond reduction catalyzed by StoA and the electron donor (Y) to StoA remain to be identified. Thioredoxin (TrxA) in the mother-cell cytoplasm might be the donor of reducing equivalents to the electron donor and indirectly to StoA.

The active site of StoA in oxidized and reduced states. A, electron density (contoured at 1.2 σ) of the active site CPPC motif of StoA reveals a mixture of oxidized and reduced states. B and C, separated representations of the active site region in oxidized and reduced states, respectively. Intercysteine sulfur distances are indicated (in Å).

Amino acid residue sequence alignment of B. subtilis sStoA used in structural and biochemical analyses, full-length StoA, and full-length ResA proteins. Invariant residues are marked in gray. The N-terminal sequence of sStoA is as confirmed by Edman degradation. Vector pGEX4T1-encoded residues in sStoA are indicated in italics. The predicted transmembrane segments of StoA and ResA are in bold letters. Stars indicate the active site residues Cys-65 and Cys-68 and conserved residue Glu-71 of StoA. Secondary structural elements are indicated above the sequence. The alignment was obtained using AlignX, Vector NTI Suite 6.0.

Electron microscopy analysis of B. subtilis endospores of strains LU60A1 (CcdA-deficient strain) (A), LUL21 (StoA- and CcdA-deficient strain) (B), and LUL30 (YkvU- and StoA-deficient strain) (C) grown for 24 h after onset of sporulation.