title: Identification of Novel Peptidyl Serine α-Galactosyltransferase Gene Family in Plants.
abstract: In plants, serine residues in extensin, a cell wall protein, are glycosylated with O-linked galactose. However, the enzyme that is involved in the galactosylation of serine had not yet been identified. To identify the peptidyl serine O-α-galactosyltransferase (SGT), we chose Chlamydomonas reinhardtii as a model. We established an assay system for SGT activity using C. reinhardtii and Arabidopsis thaliana cell extracts. SGT protein was partially purified from cell extracts of C. reinhardtii and analyzed by tandem mass spectrometry to determine its amino acid sequence. The sequence matched the open reading frame XP_001696927 in the C. reinhardtii proteome database, and a corresponding DNA fragment encoding 748 amino acids (BAL63043) was cloned from a C. reinhardtii cDNA library. The 748-amino acid protein (CrSGT1) was produced using a yeast expression system, and the SGT activity was examined. Hydroxylation of proline residues adjacent to a serine in acceptor peptides was required for SGT activity. Genes for proteins containing conserved domains were found in various plant genomes, including A. thaliana and Nicotiana tabacum. The AtSGT1 and NtSGT1 proteins also showed SGT activity when expressed in yeast. In addition, knock-out lines of AtSGT1 and knockdown lines of NtSGT1 showed no or reduced SGT activity. The SGT1 sequence, which contains a conserved DXD motif and a C-terminal membrane spanning region, is the first example of a glycosyltransferase with type I membrane protein topology, and it showed no homology with known glycosyltransferases, indicating that SGT1 belongs to a novel glycosyltransferase gene family existing only in the plant kingdom.
authors.affiliation: From the Research Center for Medical Glycoscience and Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566.
authors.forename: Fumie
authors.initials: F
authors.lastname: Saito
authors.affiliation: the Laboratory of Plant Nutrition, Faculty of Agriculture, Kyushu University, Higashi-ku, Fukuoka 812-8581.
authors.forename: Akiko
authors.initials: A
authors.lastname: Suyama
authors.affiliation: the Department of Applied Microbial Technology, Faculty of Biotechnology and Life Science, Sojo University, 4-22-1 Ikeda, Kumamoto 860-0082, and.
authors.forename: Takuji
authors.initials: T
authors.lastname: Oka
authors.affiliation: From the Research Center for Medical Glycoscience and Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Yoko-O
authors.affiliation: the Laboratory of Plant Nutrition, Faculty of Agriculture, Kyushu University, Higashi-ku, Fukuoka 812-8581, the Biotron Application Center and Organelle Homeostasis Research Center, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Matsuoka
authors.affiliation: From the Research Center for Medical Glycoscience and.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Jigami
authors.affiliation: From the Research Center for Medical Glycoscience and yohichi-shimma@aist.go.jp.
authors.forename: Yoh-Ichi
authors.initials: YI
authors.lastname: Shimma
keywords: Cell Wall; Galactose; Glycosylation; Glycosyltransferase; Plant