Table 1.
Subcellular localization and biochemical properties of SERAT proteins in grapevine.
| Isoform name | Subcellular Localization | MW (kDa) | SERAT activity (μmol min−1 mg−1) | Cys Inhibition (IC50 mM) | Interaction with OASTL | SERAT activity in CSC (μmol min−1 mg−1) |
|---|---|---|---|---|---|---|
| VvSERAT1;1 | C | 32.34 | 0.94 ± 0.36 | n. d. | + | n. d. |
| VvSERAT2;1 | P, < C | 29.46 | 9.6 ± 2 | 1.9 ± 0.56 | − | n. a. |
| VvSERAT2;2 | M, < C | 32.38 | 16 ± 3.5 | 0.16 ± 0.03 | + | 25 ± 7 |
| VvSERAT3;1 | C | n.d. | 0.13 ± 0.01 | n. d. | n. d. | n. d. |
Subcellular localization of VvSERATs has been tested by ectopic expression of VvSERAT:GFP fusion proteins in grapevine protoplasts (Figure 2). C, cytosol, P, plastids, M, mitochondrion. Theoretical molecular weight (MW) was determined for the His-VvSERAT fusion proteins. Purified recombinant His-tagged VvSERATs were tested in presence or absence of 5-molar excess of AtOASTL-B for enzymatic activity according to Wirtz et al. (2001). The inhibition constant for cysteine (IC50) was determined by titration of free VvSERATs with up to 5 mM cysteine (Figure 3). Interaction of VvSERAT with OASTL has been demonstrated by inhibition of OASTL activity upon CSC formation (Figure 3). (N = 3−5, n. a., not applicable, n.d., not determined).