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2.3.1.141

Accepted name:

galactosylacylglycerol O-acyltransferase

Reaction:

an acyl-[acyl-carrier protein] + a 2-acyl-3-O-(β-D-galactosyl)-sn-glycerol = an [acyl-carrier protein] + a 1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol

Other name(s):

acyl-acyl-carrier protein: lysomonogalactosyldiacylglycerol acyltransferase; acyl-ACP:lyso-MGDG acyltransferase; acyl-[acyl-carrier-protein]:D-galactosylacylglycerol O-acyltransferase

Systematic name:

acyl-[acyl-carrier protein]:2-acyl-3-O-(β-D-galactosyl)-sn-glycerol O-acyltransferase

Comments:

Transfers long-chain acyl groups to the sn-1 position of the glycerol residue.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 119129-68-9

References:

1.	Chen, H.-H., Wickrema, A. and Jaworski, J.G. Acyl-acyl-carrier protein: lysomonogalactosyldiacylglycerol acyltransferase from the cyanobacterium Anabaena variabilis. Biochim. Biophys. Acta 963 (1988) 493–500. [DOI] [PMID: 3143419]

[EC 2.3.1.141 created 1992]

2.4.1.46

Accepted name:

monogalactosyldiacylglycerol synthase

Reaction:

UDP-α-D-galactose + a 1,2-diacyl-sn-glycerol = UDP + a 1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol

For diagram of galactosyl diacylglycerol, click here

Other name(s):

uridine diphosphogalactose-1,2-diacylglycerol galactosyltransferase; UDP-galactose:diacylglycerol galactosyltransferase; MGDG synthase; UDP galactose-1,2-diacylglycerol galactosyltransferase; UDP-galactose-diacylglyceride galactosyltransferase; UDP-galactose:1,2-diacylglycerol 3-β-D-galactosyltransferase; 1β-MGDG; 1,2-diacylglycerol 3-β-galactosyltransferase; UDP-galactose:1,2-diacyl-sn-glycerol 3-β-D-galactosyltransferase

Systematic name:

UDP-α-D-galactose:1,2-diacyl-sn-glycerol 3-β-D-galactosyltransferase

Comments:

This enzyme adds only one galactosyl group to the diacylglycerol; EC 2.4.1.241, digalactosyldiacylglycerol synthase, adds a galactosyl group to the product of the above reaction. There are three isoforms in Arabidopsis that can be divided into two types, A-type (MGD1) and B-type (MGD2 and MGD3). MGD1 is the isoform responsible for the bulk of monogalactosyldiacylglycerol (MGDG) synthesis in Arabidopsis [4].

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 37277-55-7

References:

1.	Veerkamp, J.H. Biochemical changes in Bifidobacterium bifidum var. pennsylvanicus after cell-wall inhibition. VI. Biosynthesis of the galactosyldiglycerides. Biochim. Biophys. Acta 348 (1974) 23–34. [DOI] [PMID: 4838219]
2.	Wenger, D.A., Petipas, J.W. and Pieringer, R.A. The metabolism of glyceride glycolipids. II. Biosynthesis of monogalactosyl diglyceride from uridine diphosphate galactose and diglyceride in brain. Biochemistry 7 (1968) 3700–3707. [PMID: 5681471]
3.	Miège, C., Maréchal, E., Shimojima, M., Awai, K., Block, M.A., Ohta, H., Takamiya, K., Douce, R. and Joyard, J. Biochemical and topological properties of type A MGDG synthase, a spinach chloroplast envelope enzyme catalyzing the synthesis of both prokaryotic and eukaryotic MGDG. Eur. J. Biochem. 265 (1999) 990–1001. [DOI] [PMID: 10518794]
4.	Benning, C. and Ohta, H. Three enzyme systems for galactoglycerolipid biosynthesis are coordinately regulated in plants. J. Biol. Chem. 280 (2005) 2397–2400. [DOI] [PMID: 15590685]

[EC 2.4.1.46 created 1972, modified 2003, modified 2005]

2.4.1.184

Accepted name:

galactolipid galactosyltransferase

Reaction:

2 a 1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol = a 1,2-diacyl-3-O-[β-D-galactosyl-(1→6)-β-D-galactosyl]-sn-glycerol + a 1,2-diacyl-sn-glycerol

For diagram of galactosyl diacylglycerol, click here

Glossary:

a 1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol = monogalactosyldiacylglycerol

Other name(s):

galactolipid-galactolipid galactosyltransferase; galactolipid:galactolipid galactosyltransferase; interlipid galactosyltransferase; GGGT; DGDG synthase (ambiguous); digalactosyldiacylglycerol synthase (ambiguous); 3-(β-D-galactosyl)-1,2-diacyl-sn-glycerol:mono-3-(β-D-galactosyl)-1,2-diacyl-sn-glycerol β-D-galactosyltransferase; 3-(β-D-galactosyl)-1,2-diacyl-sn-glycerol:3-(β-D-galactosyl)-1,2-diacyl-sn-glycerol β-D-galactosyltransferase; SFR2 (gene name)

Systematic name:

1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol:1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol β-D-galactosyltransferase

Comments:

The enzyme converts monogalactosyldiacylglycerol to digalactosyldiacylglycerol, trigalactosyldiacylglycerol and tetragalactosyldiacylglycerol. All residues are connected by β linkages. The activity is localized to chloroplast envelope membranes, but it does not contribute to net galactolipid synthesis in plants, which is performed by EC 2.4.1.46, monogalactosyldiacylglycerol synthase, and EC 2.4.1.241, digalactosyldiacylglycerol synthase. Note that the β,β-digalactosyldiacylglycerol formed by this enzyme is different from the more common α,β-digalactosyldiacylglycerol formed by EC 2.4.1.241. The enzyme provides an important mechanism for the stabilization of the chloroplast membranes during freezing and drought stress.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 66676-74-2

References:

1.	Dorne, A.-J., Block, M.A., Joyard, J. and Douce, R. The galactolipid-galactolipid galactosyltransferase is located on the outer surface of the outer-membrane of the chloroplast envelope. FEBS Lett. 145 (1982) 30–34.
2.	Heemskerk, J.W.M., Wintermans, J.F.G.M., Joyard, J., Block, M.A., Dorne, A.-J. and Douce, R. Localization of galactolipid:galactolipid galactosyltransferase and acyltransferase in outer envelope membrane of spinach chloroplasts. Biochim. Biophys. Acta 877 (1986) 281–289.
3.	Heemskerk, J.W.M., Jacobs, F.H.H. and Wintermans, J.F.G.M. UDPgalactose-independent synthesis of monogalactosyldiacylglycerol. An enzymatic activity of the spinach chloroplast envelope. Biochim. Biophys. Acta 961 (1988) 38–47. [DOI]
4.	Kelly, A.A., Froehlich, J.E. and Dörmann, P. Disruption of the two digalactosyldiacylglycerol synthase genes DGD1 and DGD2 in Arabidopsis reveals the existence of an additional enzyme of galactolipid synthesis. Plant Cell 15 (2003) 2694–2706. [DOI] [PMID: 14600212]
5.	Benning, C. and Ohta, H. Three enzyme systems for galactoglycerolipid biosynthesis are coordinately regulated in plants. J. Biol. Chem. 280 (2005) 2397–2400. [DOI] [PMID: 15590685]
6.	Fourrier, N., Bedard, J., Lopez-Juez, E., Barbrook, A., Bowyer, J., Jarvis, P., Warren, G. and Thorlby, G. A role for SENSITIVE TO FREEZING2 in protecting chloroplasts against freeze-induced damage in Arabidopsis. Plant J. 55 (2008) 734–745. [DOI] [PMID: 18466306]
7.	Moellering, E.R., Muthan, B. and Benning, C. Freezing tolerance in plants requires lipid remodeling at the outer chloroplast membrane. Science 330 (2010) 226–228. [DOI] [PMID: 20798281]

[EC 2.4.1.184 created 1990, modified 2005, modified 2015]

2.4.1.241

Accepted name:

digalactosyldiacylglycerol synthase

Reaction:

UDP-α-D-galactose + 1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol = UDP + 1,2-diacyl-3-O-[α-D-galactosyl-(1→6)-β-D-galactosyl]-sn-glycerol

For diagram of galactosyl diacylglycerol, click here

Other name(s):

DGD1; DGD2; DGDG synthase (ambiguous); UDP-galactose-dependent DGDG synthase; UDP-galactose-dependent digalactosyldiacylglycerol synthase; UDP-galactose:MGDG galactosyltransferase; UDP-galactose:3-(β-D-galactosyl)-1,2-diacyl-sn-glycerol 6-α-galactosyltransferase

Systematic name:

UDP-α-D-galactose:1,2-diacyl-3-O-(β-D-galactosyl)-sn-glycerol 6-α-galactosyltransferase

Comments:

Requires Mg²⁺. Diacylglycerol cannot serve as an acceptor molecule for galactosylation as in the reaction catalysed by EC 2.4.1.46, monogalactosyldiacylglyerol synthase. When phosphate is limiting, phospholipids in plant membranes are reduced but these are replaced, at least in part, by the glycolipids digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol [3]. While both DGD1 and DGD2 are increased under phosphate-limiting conditions, DGD2 does not contribute significantly under optimal growth conditions. DGD2 is responsible for the synthesis of DGDG molecular species that are rich in C₁₆ fatty acids at sn-1 of diacylglycerol whereas DGD1 leads to molecular species rich in C₁₈ fatty acids [3]. The enzyme has been localized to the outer side of chloroplast envelope membranes.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 69913-00-4

References:

1.	Kelly, A.A. and Dörmann, P. DGD2, an Arabidopsis gene encoding a UDP-galactose-dependent digalactosyldiacylglycerol synthase is expressed during growth under phosphate-limiting conditions. J. Biol. Chem. 277 (2002) 1166–1173. [DOI] [PMID: 11696551]
2.	Härtel, H., Dörmann, P. and Benning, C. DGD1-independent biosynthesis of extraplastidic galactolipids after phosphate deprivation in Arabidopsis. Proc. Natl. Acad. Sci. USA 97 (2000) 10649–10654. [DOI] [PMID: 10973486]
3.	Kelly, A.A., Froehlich, J.E. and Dörmann, P. Disruption of the two digalactosyldiacylglycerol synthase genes DGD1 and DGD2 in Arabidopsis reveals the existence of an additional enzyme of galactolipid synthesis. Plant Cell 15 (2003) 2694–2706. [DOI] [PMID: 14600212]
4.	Benning, C. and Ohta, H. Three enzyme systems for galactoglycerolipid biosynthesis are coordinately regulated in plants. J. Biol. Chem. 280 (2005) 2397–2400. [DOI] [PMID: 15590685]

[EC 2.4.1.241 created 2005]