Structural Basis for the Interaction between Pectin Methylesterase and a Specific Inhibitor Protein

Abstract

Pectin, one of the main components of the plant cell wall, is secreted in a highly methyl-esterified form and subsequently deesterified in muro by pectin methylesterases (PMEs). In many developmental processes, PMEs are regulated by either differential expression or posttranslational control by protein inhibitors (PMEIs). PMEIs are typically active against plant PMEs and ineffective against microbial enzymes. Here, we describe the three-dimensional structure of the complex between the most abundant PME isoform from tomato fruit (Lycopersicon esculentum) and PMEI from kiwi (Actinidia deliciosa) at 1.9-Å resolution. The enzyme folds into a right-handed parallel b-helical structure typical of pectic enzymes. The inhibitor is almost all helical, with four long a-helices aligned in an antiparallel manner in a classical up-and-down fourhelical bundle. The two proteins form a stoichiometric 1:1 complex in which the inhibitor covers the shallow cleft of the enzyme where the putative active site is located. The four-helix bundle of the inhibitor packs roughly perpendicular to the main axis of the parallel b-helix of PME, and three helices of the bundle interact with the enzyme. The interaction interface displays a polar character, typical of nonobligate complexes formed by soluble proteins. The structure of the complex gives an insight into the specificity of the inhibitor toward plant PMEs and the mechanism of regulation of these enzymes.

Arabidopsis PECTIN METHYLESTERASEs Contribute to Immunity against Pseudomonas syringae

“…The significance of these domains for PME activity is not clear (Micheli, 2001;Di Matteo et al, 2005;Pelloux et al, 2007). We did not detect any correlation between the type of PME mutated and disease susceptibility to Pma ES4326 (Supplemental Table S1).…”

Inhibition of pectin methyl esterase activity by green tea catechins

“…Proteinaceous PME inhibitor (PMEI) from kiwi fruit inhibits by direct contact with the relatively wide active binding site cleft of PME , thus covering the binding site access point (D'Avino et al, 2003;Di Matteo et al, 2005). The FRET behavior exhibited in our samples ( Figure S3), in which emissions of fluorescence from the binding site tryptophan of PME are absorbed by EGCG and re-emitted at around 390 nm, suggests that the aromatic system in EGCG is interacting closely with tryptophan groups located on the PME molecule.…”

Isolation and characterization of ripening related pectin methylesterase inhibitor gene from banana fruit

“…The PMEI inhibitor protein has also been reported to be up-regulated during ripening in kiwifruit (Balestrieri et al 1990;Jolie et al 2009;Vandevenne et al 2011). Apart from the transcriptional control, the PME-PMEI complex has also been shown at structural level (Di Matteo et al 2005;Hao et al 2008;Hothorn et al 2004) for the regulation of PMEs. Furthermore, PMEIs have been shown to have a broad specificity towards different PME isoforms (Wu et al 2002).…”

“…Based on the sequence and phylogenetic analysis, the putative PME/Invertase inhibitor obtained in the present study appears to be a pectin methylesterase inhibitor (PMEI) and thus it was christened as MaPMEI. The PMEIs and their inhibitory activity have also been reported from different plants (Di Matteo et al 2005;Hao et al 2008;Hong et al 2010;Irifune et al 2004;Wu et al 2002). The production of transgenic crops containing PMEI genes is also an attractive possibility for inactivating endogenous PME activity (Irifune et al 2004;Jiang et al 2002).…”