Bifunctional glycosyltransferases catalyze both extension and termination of pectic galactan oligosaccharides

TY - JOUR

T1 - Bifunctional glycosyltransferases catalyze both extension and termination of pectic galactan oligosaccharides

AU - Laursen, Tomas

AU - Stonebloom, Solomon H.

AU - Pidatala, Venkataramana R.

AU - Birdseye, Devon S.

AU - Clausen, Mads H.

AU - Mortimer, Jenny C.

AU - Scheller, Henrik Vibe

N1 - © 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.

PY - 2018/4

Y1 - 2018/4

N2 - Pectins are the most complex polysaccharides of the plant cell wall. Based on the number of methylations, acetylations and glycosidic linkages present in their structures, it is estimated that up to 67 transferase activities are involved in pectin biosynthesis. Pectic galactans constitute a major part of pectin in the form of side-chains of rhamnogalacturonan-I. In Arabidopsis, galactan synthase 1 (GALS1) catalyzes the addition of galactose units from UDP-Gal to growing β-1,4-galactan chains. However, the mechanisms for obtaining varying degrees of polymerization remain poorly understood. In this study, we show that AtGALS1 is bifunctional, catalyzing both the transfer of galactose from UDP-α-d-Gal and the transfer of an arabinopyranose from UDP-β-l-Arapto galactan chains. The two substrates share a similar structure, but UDP-α-d-Gal is the preferred substrate, with a 10-fold higher affinity. Transfer of Arapto galactan prevents further addition of galactose residues, resulting in a lower degree of polymerization. We show that this dual activity occurs both in vitro and in vivo. The herein described bifunctionality of AtGALS1 may suggest that plants can produce the incredible structural diversity of polysaccharides without a dedicated glycosyltransferase for each glycosidic linkage.

AB - Pectins are the most complex polysaccharides of the plant cell wall. Based on the number of methylations, acetylations and glycosidic linkages present in their structures, it is estimated that up to 67 transferase activities are involved in pectin biosynthesis. Pectic galactans constitute a major part of pectin in the form of side-chains of rhamnogalacturonan-I. In Arabidopsis, galactan synthase 1 (GALS1) catalyzes the addition of galactose units from UDP-Gal to growing β-1,4-galactan chains. However, the mechanisms for obtaining varying degrees of polymerization remain poorly understood. In this study, we show that AtGALS1 is bifunctional, catalyzing both the transfer of galactose from UDP-α-d-Gal and the transfer of an arabinopyranose from UDP-β-l-Arapto galactan chains. The two substrates share a similar structure, but UDP-α-d-Gal is the preferred substrate, with a 10-fold higher affinity. Transfer of Arapto galactan prevents further addition of galactose residues, resulting in a lower degree of polymerization. We show that this dual activity occurs both in vitro and in vivo. The herein described bifunctionality of AtGALS1 may suggest that plants can produce the incredible structural diversity of polysaccharides without a dedicated glycosyltransferase for each glycosidic linkage.

U2 - 10.1111/tpj.13860

DO - 10.1111/tpj.13860

M3 - Journal article

C2 - 29418030

SN - 0960-7412

VL - 94

SP - 340

EP - 351

JO - Plant Journal

JF - Plant Journal

IS - 2

ER -