OPEN ACCESS ARTICLE

This Article Free via Open Access: OA OA Full Text Full Text (PDF) Supplemental Data OA All Versions of this Article: 145/2/504    most recent pp.107.104679v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Plant Physiol. Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ibar, C. Articles by Orellana, A. Search for Related Content PubMed PubMed Citation Articles by Ibar, C. Articles by Orellana, A. Agricola Articles by Ibar, C. Articles by Orellana, A.

BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

The Import of S-Adenosylmethionine into the Golgi Apparatus Is Required for the Methylation of Homogalacturonan^1,[W],[OA]

Millennium Nucleus in Plant Cell Biology, Center of Plant Biotechnology, Andrés Bello University, República 217, Santiago, Chile

S-adenosylmethionine (SAM) is the substrate used in the methylation of homogalacturonan (HGA) in the Golgi apparatus. SAM is synthesized in the cytosol, but it is not currently known how it is then transported into the Golgi. In this study, we find that HGA methyltransferase is present in Golgi-enriched fractions and that its catalytic domain faces the lumen of this organelle. This suggests that SAM must be imported into the Golgi. We performed uptake experiments using [methyl-¹⁴C]SAM and found that SAM is incorporated into the Golgi vesicles, resulting in the methylation of polymers that are sensitive to pectinase and pectin methylesterase but not to proteases. To avoid detecting the transfer reaction, we also used [carboxyl-¹⁴C]SAM, the uptake of which into Golgi vesicles was found to be sensitive to temperature, detergents, and osmotic changes, and to be saturable with a K_m of 33 µM. Double-label uptake experiments using [methyl-³H]SAM and [carboxyl-¹⁴C]SAM also revealed a time-dependent increase in the ³H to ¹⁴C ratio, suggesting that upon transfer of the methyl group, the resulting S-adenosylhomocysteine is not accumulated in the Golgi. SAM incorporation was also found to be inhibited by S-adenosylhomocysteine, whereas UDP-GalA, UDP-GlcA, and acetyl-CoA had no effect. DIDS, a compound that inhibits nucleotide sugar transporters, also had little effect upon SAM incorporation. Interestingly, the combination of UDP-GalA + acetyl-CoA or UDP-GlcA + acetyl-CoA produced a slight increase in the uptake of SAM. These results support the idea that a SAM transporter is required for HGA biosynthesis.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ariel Orellana (aorellana{at}unab.cl).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.104679

^* Corresponding author; e-mail aorellana{at}unab.cl.

Received June 26, 2007; accepted August 23, 2007; published August 31, 2007.

Related articles in Plant Physiol.:

On the Inside

Peter V. Minorsky
Plant Physiol. 2007 145: 291-292. [Full Text]