The Arabidopsis (Arabidopsis thaliana) genome encodes 51 proteins annotated as serine carboxypeptidase-like (SCPL) enzymes. Nineteen of these SCPL proteins are highly similar to one another, and represent a clade that appears to be unique to plants. Two of the most divergent proteins within this group have been characterized to date, sinapoyl-glucose (Glc):malate sinapoyltransferase and sinapoyl-Glc:choline sinapoyltransferase. The fact that two of the least related proteins within this clade are acyltransferases rather than true serine carboxypeptidases suggests that some or all of the remaining members of this group may have similar activities. The gene that encodes sinapoyl-Glc:malate sinapoyltransferase (sinapoyl-Glc accumulator1 [SNG1]: At2g22990) is one of five SCPL genes arranged in a cluster on chromosome 2. In this study, an analysis of deletion mutant lines lacking one or more genes in this SCPL gene cluster reveals that three of these genes also encode sinapoyl-Glc-dependent acyltransferases. At2g23000 encodes sinapoyl-Glc:anthocyanin acyltransferase, an enzyme that is required for the synthesis of the sinapoylated anthocyanins in Arabidopsis. At2g23010 encodes an enzyme capable of synthesizing 1,2-disinapoyl-Glc from two molecules of sinapoyl-Glc, an activity shared by SNG1 and At2g22980. Sequence analysis of these SCPL proteins reveals pairwise percent identities that range from 71% to 78%, suggesting that their differing specificities for acyl acceptor substrates are due to changes in a relatively small subset of amino acids. The study of these SCPL proteins provides an opportunity to examine enzyme structure-function relationships and may shed light on the role of evolution of hydroxycinnamate ester metabolism and the SCPL gene family in Arabidopsis and other flowering plants.

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11
9,2	xXSin	126.7	107.1	149.6	139.8	149.6	107.1	148.0	115.7	168.6	56.9	56.9
9	bDGlcp	94.2	74.4	76.2	71.4	79.3	62.4
	xXSin	126.3	107.3	149.6	140.3	149.6	107.3	149.1	114.7	167.4	56.9	56.9


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9	H10	H11
9,2	xXSin	-	6.85	-	-	-	6.85	7.63	6.41	-	3.84	3.84
9	bDGlcp	5.80	5.07	3.73	3.518	3.515	3.76-3.89
	xXSin	-	6.89	-	-	-	6.89	7.64	6.32	-	3.86	3.86


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9	C10/H10	C11/H11
9,2	xXSin		107.1/6.85				107.1/6.85	148.0/7.63	115.7/6.41		56.9/3.84	56.9/3.84
9	bDGlcp	94.2/5.80	74.4/5.07	76.2/3.73	71.4/3.518	79.3/3.515	62.4/3.76-3.89
	xXSin		107.3/6.89				107.3/6.89	149.1/7.64	114.7/6.32		56.9/3.86	56.9/3.86

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

COc1cc(/C=C/C(=O)O[C@@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@H]2OC(=O)/C=C/c2cc(OC)c(O)c(OC)c2)cc(OC)c1O

592.55 g/mol (C₂₈H₃₂O₁₄)