Multiple Forms of Pectinesterase are Present in Tomato and Other Fruit

Pectinesterase Isoforms

There are now a large number of tomato PE N-terminal protein sequences available in the literature. These are shown in the table below:

Table 1. Tomato PE N-terminal sequences
Sequence	Name	Cultivar	Reference
IIANAVVAQDGTGDYQYLAEAVAAA	?	Immuna	Markovic & Jörnvall (1986)
IIANAVVAQDGTGDYQLTAEAVAAA	PE-A	Ailsa Craig	Warrilow et al. (1994)
LSXGQVESGLAPXLPYLQGKGPLGG	PE-C	Ailsa Craig	Warrilow et al. (1994)
EDPYRYFDW	PE3	Ailsa Craig	Zhang, 1994
IIANAVVAQDGTGKYRTLAEAV	PEIII	Short Red	Pressey & Woods, (1992)
IIANAVVAQDGTGDYQTLAEAV	PEIV	Better Boy	Pressey & Woods (1992)
IGANAVVAKDGTGKYRTLAEAVAAA	pPE1	Ailsa Craig	Ray et al. (1988)
IIANAVVAQDGTGDYQTLAEAVAAA	pB8	Ailsa Craig	Hall et al. (1994)
IGANAVVAKDGTGKYRTLAEAVAAA	pB16	Ailsa Craig	Hall et al. (1994)

As can be seen from the table, virtually all of the sequences are very similar to the first PE protein sequenced by Markovic & Jörnvall. This corresponds to the main isoform known as PE2. Some of the minor differences between the N-terminal sequences were thought to be due to differences between the tomato varieties studied. However, the pB8 & pB16 sequences were both derived from distinct cDNA clones of the cultivar Ailsa Craig, so perhaps there are "sub-isoforms" of PE2. To confuse matters further, the sequences of PE-C (PE1) and PE3 share no homology to the rest. Our sequencing of the putative cDNA for PE3 shows no homology to PE2, so these could be PEs unrelated to PE2.

Multiple Forms of Pectinesterase are Present in Tomato and Other Fruit

Pectinesterase Isoforms

Further Reading