Figure 1.

Proposed Topological Arrangement of Plastid Arabidopsis LTO1.

The proposed topological arrangement of Arabidopsis LTO1 in the thylakoid membrane was deduced from the analysis of PhoA/LacZα sandwich fusions expressed in bacteria (Table 1). The p-side corresponds to the lumen of the thylakoid, and the n-side corresponds to the stroma of the chloroplast. LTO1 is represented as a thick thread with its transmembrane domains in the lipid bilayer and extramembranous regions. The LTO1 N-terminal end faces the stroma, while the C-terminal domain, corresponding to the thioredoxin-like domain, is exposed to the thylakoid lumen. The arrows indicate the positions of in-frame sandwich fusions with the Pho-Lac minireporter, which corresponds to alkaline phosphatase fused to the α fragment of β-galactosidase. Fusions at positions 74 (1), 113 (2), 191 (3), 195 (4), and 573 (5) are indicated on the drawing by arrows. Strictly conserved Cys residues are marked (C). Conserved Cys residues within CXXC motifs are highlighted in white.