Review Article Open Access Kohli et al., J Bioprocess Biotech 2015, 5:5 DOI: 10.4172/2155-9821.1000227 Volume 5 • Issue 5 • 1000227 J Bioprocess Biotech ISSN:2155-9821 JBPBT, an open access journal *Corresponding author: Reena Gupta, Professor, Department of Biotechnology, Himachal Pradesh University, Summer Hill, Shimla-171005, India, Tel: 91-177-283- 1948; Fax: 91-177-283-1948; E-mail: reenagupta_2001@yahoo.com Received February 17, 2015; Accepted May 15, 2015; Published May 20, 2015 Citation: Kohli P, Kalia M, Gupta R (2015) Pectin Methylesterases: A Review. J Bioprocess Biotech 5: 227 doi:10.4172/2155-9821.1000227 Copyright: © 2015 Kohli P et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract Pectin methylesterase (PME) is the frst enzyme acting on pectin, a major component of plant cell wall. PME catalyzes reactions according to the double-displacement mechanism. In plants, PMEs can be classifed on the basis of presence or absence of the PRO domain in pectin methylesterase into Type 1 and Type II. Type1 contains one to three PRO domains and two or three introns, type II PMEs are without PRO domain and with fve or six introns. Once PMEs are secreted into the cell wall, mature PMEs exhibit three different modes of action: single chain mechanism, multiple chain mechanism and multiple attack mechanism. For bacterial and plant PMEs, single chain and multiple chain mechanism is used and for fungal PMEs only multiple chain mechanism has been proposed. PME activity is regulated by differential expression both spatially and temporally. Pectin Methylesterases: A Review Pooja Kohli, Manmohit Kalia and Reena Gupta Department of Biotechnology, Himachal Pradesh University, Summer Hill, Shimla-171005, INDIA Keywords: Pectin methylesterase; Demethylestrifcation; Catalysis; Transacylation; Fruit frming Introduction Pectinolytic enzymes or pectinases are a heterogeneous group of enzymes that hydrolyze the pectic substances present in plants. Tey include polygalacturonases, pectin lyase, and PME that hydrolyze the glycosidic bonds of pectic substances. Pectin methylesterase (E.C. 3.1.1.11), a methyl ester group hydrolytic enzyme is produced by plants, pathogenic fungi, and bacteria also constantly being used in the wine, juice, and other food industries [1]. In Arabidopsis PMEs, it was revealed that PMEs have unique patterns of methylesterifcation that provide immunity to Pseudomonas syringae pv maculicola ES4326 (Pma ES4326) [2]. Pectin methylesterase catalyzes reactions according to the double-displacement mechanisms, de-esterifcation through transferring the C 6 carboxyl groups in the pectin-PME complexes to water molecules altering the degree and pattern of methyl esterifcation and transacylation through transferring the C 6 carboxyl groups to the hydroxyl groups of another pectin molecules and resulting in the formation of high molecular weight pectins with new non-methoxy ester linkages [3-8]. PME has been purifed and characterized from several fruit sources including tomato [9], orange, papaya [10], apple [11], kiwi [12], grapefruit pulp and mandarin orange fruit [13]. PMEs having diverse and well-defned activities could be useful for making “designer pectins” for fulflling new demands from food industry. It has been reported that PME activity is partly regulated by PMEI (Pectin methylestearse inhibitor) [14,15] For example, in fax (Linum usitatissimum) Lu PMEs gene family, most highly conserved residues were catalytic residues, while in Lu PMEIs gene family, cysteine’s forming disulphide bridges between helices α2 and α3 were found to be conserved residues [16]. Te modifcation of pectin by PMEs is known to modify the quality of plant-based food products. It has been recently confrmed that PME has a defnite role in plant defence system by virus induced gene silencing of PME gene in Nicotiana benthamiana [17]. Types of Pectin Methylesterases Several pectin methylesterase isoforms difering in molecular weight, pI and biochemical activity were detected in all higher plants examined so far as well as in a number of plant pathogenic fungi and bacteria [18]. In a study, a basic PME which is an isoform of B3a found to be encoded by LuPME3 from Linum usitatissimum and play great role in fax root development [19]. Pectin methylesterase belongs to class 8 (CE-8) of the carbohydrate esterase [20]. Plant pectin methylesterase belong to large multigene families. For instance, in Arabidopsis thaliana, 66 open reading frames (ORF) have been annotated as putative full- length PMEs. Tere are 89 PME ORFs in Populus trichocarpa [21] whereas this number is substantially lower in Oryza sativa with 35 ORFs, probably due to the low level of pectin in their cell wall. Higher plant PMEs are frequently organised in pre-pro-proteins. Te PRE domain leading to the export of PMEs to the cell wall is formed by a common type signal peptide (SP) and by a transmembrane domain (TM or signal anchor). Diferent PMEs possess one, both, or neither of these motifs. Tose with neither motif are classifed as putatively soluble isoforms. Te mature, active part of the protein (PME domain) is preceded by an N-terminal extension (PRO region) that shares similarities with the pectin methylesterase inhibitors. Te PRO-regions can vary in length and shows a relatively low level of amino acid identity between isoforms [22]. In Arabidopsis, the isoelectric point of the 26 PME domains tends to be basic whereas that of the PRO region is neutral or acidic [23,24]. Similar diferences in length and isoelectric point between PRO and PME domains have also been found in several other species [25], and might infuence the optimal pH activities of specifc isoforms. Pectin methylesterases can be classifed on the basis of presence or absence of the PRO domain into Type I and Type II. In PMEs Type I (500-900 amino acids; 52-105 kDa) there are 1-3 PRO domains and two or three introns (Figure 1) whereas PMEs Type II (250 to 400 amino acids; 27-45 kDa) contain no PRO domain with fve or six introns [26,27]. Te Type II sequences have a structure close to that of the PMEs identifed in phytopathogenic organisms (bacteria, fungi). Mode of Action of Mature Pectin Methylesterase Afer their secretion into the cell wall, mature PMEs could exhibit three diferent modes of action (I) a single-chain mechanism where the enzyme converts all substrate sites on the polymeric chain, (II) Journal of Bioprocessing & Biotechniques J o u r n a l o f B i o p r o c e s s i n g & B i o t e c h n i q u e s ISSN: 2155-9821