Main characterized components of the disulfide bond formation pathway in the ER, chloroplasts, and mitochondria of plant cells. (a) Schematic illustration of ERO1 and PDIs in the plant ER. (b) Schematic illustration of a VKOR homolog (LTO1) and thiol-disulfide oxidoreductases (PDIL1;3, LQY1, and CYO1) in chloroplasts. (c) Schematic illustration of ERV1 and MIA40 in mitochondria. In disulfide-generating enzymes (ERO1, LTO1, and ERV1), the predicted active-site Cys pairs, shuttle Cys pairs, and regulatory Cys pairs are indicated with red, blue, and green circles, respectively. The FAD cofactor is shown in yellow. No cofactor of LTO1 has been identified yet (question mark circled in orange). In disulfide carrier proteins and TRX domain of LTO1, the predicted redox-active Cys pairs (CxxC in TRX domains and Zn finger domains, CPC in MIA40) are indicated with white circles. The predicted structural Cys pairs in MIA40 (Cx9C) and ERV1 (Cx16C) are indicated with brown lines. Redox-active TRX (a and domains; blue boxes), redox-inactive TRX (b and ; white boxes), α-helical D (white box), VKOR (green box), DnaJ Zn finger (Znf; orange boxes), and Erv1/ALR (cyan box) domains are predicted by NCBI Conserved Domain searches (http://www.ncbi.nlm.nih.gov/Structure/cdd/cdd.shtml). Transmembrane helices (TMD; purple boxes) are predicted by TMHMM v. 2.0 (http://www.cbs.dtu.dk/services/TMHMM/). Acidic N-terminal c domains are also indicated (white boxes). Amino acid sequence data can be found in the GenBank/EMBL databases under the following accession numbers: OsERO1, OSJNEc05N03; OsPDIL1;1, NP_001067436; AtPDIL1;4, NP_001190581; AtPDIL2;1, NP_973708; OsPDIL2;3, NP_001063331; AtPDIL1;3, NP_191056; AtLTO1, NP_567988; AtLQY1, NP_177698; AtCYO1, NP_566627; AtERV1, NP_564557; AtMIA40, NP_680211.
