Table I.
Important protein families involved in primary wall metabolism
| CWN Abr | CAZy | ||||
|---|---|---|---|---|---|
| 1 | Monosaccharide activation and interconversion | ||||
| 1.1 | Sugar 1-kinases (Ara1) | S1K | |||
| 1.2 | Nucleotide-sugar pyrophosphorylases | NSPP | |||
| 1.2.1 | GDP-Man pyrophosphorylase (CYT1) | GMP | |||
| 1.2.2 | UDP-Glc pyrophosphorylase | UGP | |||
| 1.3 | Nucleotide-sugar interconversion: NAD-dependent epimerase/dehydratase superfamily | ||||
| 1.3.1 | UDP-d-Glc 4-epimerases (UGE1-5) | UGE | |||
| 1.3.2 | UDP-d-GalUA 4-epimerases (GAE1-6) | GAE | |||
| 1.3.3 | UDP-l-rhamnose synthases (RHM1-3, UER1) | RHM | |||
| 1.3.4 | UDP-d-apiose/Xyl synthases (AXS1-2, AUD1-3, SUD1-3) | UXS | |||
| 1.3.5 | UDP-d-Xyl 4-epimerase (UXE1-4; MUR4) | UXE | |||
| 1.3.6 | GDP-d-Man 3,5-epimerase | GME | |||
| 1.3.7 | GDP-4-keto-6-deoxy-d-Man-3,5-epimerase-4-reductase (GER1-2) | GER | |||
| 1.3.8 | GDP-d-Man-4,6-dehydratase (GMD1-2; MUR1) | GMD | |||
| 1.4 | Nucleotide-sugar interconversion: nucleotide sugar dehydrogenase superfamily | ||||
| 1.4.1 | UDP-d-Glc dehydrogenases (UGD1-4) | UGD | |||
| 2 | Polysaccharide synthesis | ||||
| 2.1 | Cellulose and galactomannan | ||||
| 2.1.1 | Cellulose synthases (CESAx) | CES | GT2 | ||
| 2.1.2 | Cellulose and β-mannan synthase-like (CSLx) | CSL | GT2 | ||
| 2.2 | Hemicellulose | ||||
| 2.2.1 | Reversibly glycosylated polypeptides | RGP | |||
| 2.2.2 | Xyloglucan galactosyltransferases (MUR3) | XGT | GT47 | ||
| 2.2.3 | Xyloglucan fucosyltransferase (MUR2) | XFT | GT37 | ||
| 2.2.4 | Xyloglucan xylosyltransferases and galactomannan gal-transferases | XXT | GT34 | ||
| 2.2.5 | Glucuronoarabinoxylan* | GAX | |||
| 2.3 | Pectin (selection) | ||||
| 2.3.1 | Homogalacturonan (HG, involvement of GT8) | ||||
| 2.3.2 | Xylogalacturonan (XGA)* | ||||
| 2.3.3 | Rhamnogalacturonan I (RG-I, involvement of RHM)* | ||||
| 2.3.4 | Rhamnogalacturonan II (RG-II, involvement of XGT; GUT1) | ||||
| 2.3.5 | Arabinogalactan I (AG-I)* | ||||
| 2.3.6 | Arabinogalactan II (AG-II)* | ||||
| 2.3.7 | Arabinan (A)* | ||||
| 2.4 | Callose | ||||
| 2.4.1 | Glucan synthase-like | GSL | GT48 | ||
| 2.5 | Other glycosyl transferases | ||||
| 2.5.1 | Glycosyltransferases (Qua1; associated with HG biosynthesis) | GT8 | GT8 | ||
| 3 | Reassembly and Degradation | ||||
| 3.1 | Cell expansion | ||||
| 3.1.1 | Expansins (EXP10) | EXP | |||
| 3.1.2 | Yieldins | GH18 | GH18 | ||
| 3.2 | Hemicellulose reassembly | ||||
| 3.2.1 | Xyloglucan endotransglucosylases/hydrolases | XTH | GH16 | ||
| 3.3 | Glycoside hydrolases | ||||
| 3.3.1 | β-Galactosidase | BGAL | GH35 | ||
| 3.3.2 | Endo-1,4-β-glucanase | GH9 | GH9 | ||
| 3.3.3 | Glucan 1,3-β-glucosidase | GH17 | GH17 | ||
| 3.3.4 | Glycoside hydrolase: polyGalAase, Rha-GalAase | GH28 | GH28 | ||
| 3.3.5 | Xylan degradation | GH10 | GH10, 43 & 51 | ||
| 3.4 | Lyases | ||||
| 3.4.1 | Pectate and pectin lyases | PL1 | PL1 | ||
| 3.4.2 | Rhamnogalacturonan I lyases | PL4 | PL4 | ||
| 3.5 | Esterases | ||||
| 3.5.1 | Pectin methyl esterases | PME | CE8 | ||
| 3.5.2 | Pectin acetylesterases | PAE | CE13 | ||
| 3.5.3 | Feruloyl esterases | FE | CE1 | ||
| 4 | Structural proteins | ||||
| 4.1 | Hyp-rich glycoproteins or extensins | HRGP | |||
| 4.2 | Leu-rich repeat extensins | LRX | |||
| 4.3 | Pro-rich proteins | PRP | |||
| 4.4 | Gly-rich proteins | GRP | |||
| 4.5 | Arabinogalactan proteins | AGP | |||
| 5 | Glycoprotein glycosyltransferases | ||||
| 5.1 | Glycoprotein fucosyltransferases | GFT | GT10 | ||
| 5.2 | Glycosyltransferases | GT31a/b | GT31 | ||
The protein classes in this table are primarily organized by sequence similarity. The superimposed product classifications are not intended to be complete. *, Several listed polysaccharide classes are still lacking sequence information associated with the biosynthesis of their backbone structure. Additionally, the boundaries of sequence- and product-based categorization are often not in alignment. For instance, the β-mannan synthase is functionally involved in hemicellulose synthesis, and by sequence similarity it is a member of the CSL superfamily. CWN Abr, Family abbreviations used in CWN. The corresponding family identifiers of the CAZy database are listed in the last column: GH, glycoside hydrolase; GT, glycosyltransferase; PL, polysaccharide lyase; CE, carbohydrate esterase.