Taxonomic distribution of proteins containing PMEI domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing PMEI domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Kiwi protein inhibitor of pectin methylesterase amino-acid sequence andstructural importance of two disulfide bridges.

Camardella L, Carratore V, Ciardiello MA, Servillo L, Balestrieri C, Giovane A
Eur J Biochem. 2000; 267: 4561-5

A protein acting as a powerful inhibitor of plant pectin methylesterasewas isolated from kiwi (Actinidia chinensis) fruit. The completeamino-acid sequence of the pectin methylesterase inhibitor (PMEI) wasdetermined by direct protein analysis. The sequence comprises 152amino-acid residues, accounting for a molecular mass of 16 277 Da. Thefar-UV CD spectrum indicated a predominant alpha-helix conformation in thesecondary structure. The protein has five cysteine residues but neithertryptophan nor methionine. Analysis of fragments obtained after digestionof the protein alkylated without previous reduction identified twodisulfide bridges connecting Cys9 with Cys18, and Cys74 with Cys114;Cys140 bears a free thiol group. A database search pointed out asimilarity between PMEI and plant invertase inhibitors. In particular, thefour Cys residues, which in PMEI are involved in the disulfide bridges,are conserved. This allows us to infer that also in the homologousproteins, whose primary structure was deduced only by cDNA sequencing,those cysteine residues are engaged in two disulfide bridges, andconstitute a common structural motif. The comparison of the sequence ofthese inhibitors confirms the existence of a novel class of proteins withmoderate but significant sequence conservation, comprising plant proteinsacting as inhibitors of sugar metabolism enzymes, and probably involved invarious steps of plant development.

A glycoprotein inhibitor of pectin methylesterase in kiwi fruit.Purification by affinity chromatography and evidence of a ripening-relatedprecursor.

Giovane A, Balestrieri C, Quagliuolo L, Castaldo D, Servillo L
Eur J Biochem. 1995; 233: 926-9

The pectin methylesterase inhibitor from kiwi fruit (Actinidia chinensis)was purified by a single-step procedure based on affinity chromatography.Partially purified tomato pectin methylesterase was covalently bound toSepharose. The affinity resin strongly and selectively binds theinhibitor, which could be eluted in high yield as a single, homogeneousand sharp peak by high salt concentration at pH 9.5 without loss ofinhibitory activity. The purified protein possesses a molecular mass of 18kDa, as estimated by SDS/PAGE, whereas by gel filtration under nativeconditions, its molecular mass appears to be 25 kDa. The inhibitorinteracts with pectin methylesterase, forming a 1:1 complex, asdemonstrated by gel-filtration experiments. The inhibitor wasglycosylated. Its glycidic portion can be removed by digestion withN-glycosidase F after protein denaturation and, to a minor extent, bydigestion with N-glycosidase H. No glycidic residue could be removed bydigesting the native protein with those N-glycosidases. Antibodies againstpectin methylesterase inhibitor were raised in rabbits and used toevidence protein expression during fruit ripening. The results showed thatthe inhibitor is present in the unripe fruit as an inactive precursor witha higher molecular mass (30 kDa) and is transformed into the activeprotein, most likely by proteinase action, during the course of theripening process.