TABLE 1.
Substrate specificities and affinities of substrate-binding proteins as determined by fluorescence spectroscopy
| Type of SBP | Locus | Substrate(s) bound | Kd (μM)a | Neighboring enzyme
|
|
|---|---|---|---|---|---|
| Locus | Activityb | ||||
| Archaea-related oligosaccharide SBPsg | TM0031 (bglE) | Cellobiose | 0.9 ± 0.2 | TM0024 | Laminarinase (LamA, extracellular) |
| Laminaribiose | 0.8 ± 0.2 | TM0025 | β-Glucosidase (BglB, cytoplasmic) | ||
| TM0071 (xloE) | Xylobiosec | + | TM0061 | Endo-β-1,4-xylanase A (XylA, extracellular) | |
| Xylotriosec | TM0069 | Mannonate hydrolase (cytoplasmic) | |||
| TM0070 | Endo-β-1,4-xylanase B (XynB, extracellular) | ||||
| TM0076 | Xylosidase (XloA, cytoplasmic) | ||||
| TM0300 (gloE) | Xyloglucan hepta-, octa-, and nonasaccharides with β-1,4 tetraglucosyl backbones | + | TM0305 | Endoglucanase/xyloglucanase (extracellular) | |
| TM0306 | α-Fucosidase (cytoplasmic) | ||||
| TM0308 | α-Xylosidase (XylQ, cytoplasmic) | ||||
| TM0310 | β-Galactosidase (cytoplasmic) | ||||
| TM0460 | No tested sugars bind | None | |||
| TM1150 | No tested sugars bind | None | |||
| TM1199 | No tested sugars bind (pectin hydrolysate) | TM1192 | α-Galactosidase (cytoplasmic) | ||
| TM1193 | β-Galactosidase (cytoplasmic) | ||||
| TM1195 | β-Galactosidase (cytoplasmic) | ||||
| TM1201 | Arabinogalactan endo-β-1,4-galactosidase (extracellular) | ||||
| TM1223 (manE) | β-1,4-Mannobiose | 13 ± 1 | TM1227 | Endo-β-1,4-mannosidase (extracellular) | |
| TM1226 (manD) | β-1,4-Mannobiose | 15 ± 2 | TM1227 | Endo-β-1,4-mannosidase (extracellular) | |
| β-1,4-Mannotriose | 1.05 ± 0.4 | ||||
| β-1,4-Mannotetraose | 0.38 ± 0.1 | ||||
| β-1,4-Galactosyl mannobiose | 10 ± 1 | ||||
| Cellobiose | 9.5 ± 1 | ||||
| Sugar SBPs | TM0114 (xylE) | Xylose | 0.0135 ± 0.001 | TM0113 | Xylanase (XylU, extracellular) |
| TM0116 | Putative xylulokinase | ||||
| TM0418 (inoE) | myo-Inositol | 24.0 ± 1 | None | ||
| TM0432 (aguE) | α-1,4-Digalacturonic acid | 0.25 ± 0.05 | TM0433 | Pectate lyase (PelA, extracellular) | |
| TM0434 | α-Glucuronidase (Agu, cytoplasmic) | ||||
| TM0437 | Exo-α-galacturonidase (cytoplasmic) | ||||
| TM0595 | No tested sugars bind | None | |||
| TM0810 | No tested sugars bind | TM0809d | β-N-Acetylglucosaminidase (cytoplasmic) | ||
| TM0958 (rbsB) | Ribose | 0.4 ± 0.5e | None | ||
| TM1204 (malE1)f | Maltose | 24 ± 1 | TM1192 | α-Galactosidase (cytoplasmic) | |
| Maltotriose | 0.008 ± 0.0005 | TM1193 | β-Galactosidase (cytoplasmic) | ||
| β-1,4-Mannotetraose | 38 ± 1 | TM1195 | β-Galactosidase (cytoplasmic) | ||
| TM1201 | Arabinogalactan endo-β-1,4-galactosidase (extracellular) | ||||
| TM1839 (malE2)f | Maltose | 8.4 ± 1 | TM1834 | α-Glucosidase (cytoplasmic) | |
| Maltotriose | 11 ± 1.5 | TM1835 | Cyclomaltodextrinase (cytoplasmic) | ||
| Trehalose | 9.5 ± 1 | TM1840 | α-Amylase (extracellular) | ||
| TM1845 | Pullulanase (extracellular) | ||||
| TM1855 | No tested sugars bind (xanthan gum) | TM1851 | α-Mannosidase (cytosolic) | ||
+, a change in fluorescence is detectable, but the data do not fit a simple model to determine a Kd value. Values are shown ±1 standard deviation. Dissociation constants were measured at 20°C, except for that of RbsB, which was measured at 55°C.
Enzymes whose genes encode potential signal peptides are listed as “extracellular,” while those that do not are listed as “cytoplasmic.”
Ninety-five-percent pure; remainder, other xylooligosaccharides.
TM0809 is similar (E value of 10−178) to a β-N-acetylglucosaminidase from T. neapolitana (CbsA, GenBank accession number AF34391).
Value determined by equilibrium dialysis using radiolabeled ribose, as described in the text.
Data for substrate affinities for MalE1 and MalE2 were published previously (33).
Annotated as oligopeptide SBPs.