Pectin is a major component of primary cell walls of all land plants and encompasses a range of galacturonic acid-rich polysaccharides Three major pectic polysaccharides (homogalacturonan, rhamnogalacturonan-I and rhamnogalacturonan-II) are thought to occur in all primary cell walls This review surveys what is known about the structure and function of these pectin domains The high degree of structural complexity and heterogeneity of the pectic matrix is produced both during biosynthesis in the endomembrane system and as a result of the action of an array of wall-based pectin-modifying enzymes Recent developments in analytical techniques and in the generation of anti-pectin probes have begun to place the structural complexity of pectin in cell biological and developmental contexts The in muro de-methyl-esterification of homogalacturonan by pectin methyl esterases is emerging as a key process for the local modulation of matrix properties Rhamnogalacturonan-I comprises a highly diverse population of spatially and developmentally regulated polymers, whereas rhamnogalacturonan-II appears to be a highly conserved and stable pectic domain Current knowledge of biosynthetic enzymes, plant and microbial pectinases and the interactions of pectin with other cell wall components and the impact of molecular genetic approaches are reviewed in terms of the functional analysis of pectic polysaccharides in plant growth and development

https://link.springer.com/content/pdf/10.1023/A:1010662911148.pdf

Pectin: cell biology and prospects for functional analysis

β Galactosidases have been obtained from microorganisms such as fungi, bacteria and yeasts; plants, animals cells, and from recombinant sources. The enzyme has two main applications; the removal of lactose from milk products for lactose intolerant people and the production of galactosylated products. In order to increase their stability, reusability, and use in continuous reactors, these enzymes have been immobilized on both organic and inorganic support via adsorption, covalent attachment, chemical aggregation, microencapsulation, and entrapment. Free and immobilized preparations of β galactosidases have been exploited in various applications such as industrial, biotechnological, medical, analytical, and in different other applications. β galactosidase is widely used in food industry to improve sweetness, solubility, flavor, and digestibility of dairy products. Immobilized β galactosidases are employed for the continuous hydrolysis of lactose from whey and milk in a number of reactors such as hollow fiber reactors, tapered column reactors, packed bed reactors, fluidized bed reactors etc.

β Galactosidases and their potential applications: a review

During our search for a cDNA encoding β-galactosidase II, a β-galactosidase/exogalactanase (EC 3.2.1.23) present during tomato (Lycopersicon esculentum Mill.) fruit ripening, a family of seven tomato β-galactosidase (TBG) cDNAs was identified. The shared amino acid sequence identity among the seven TBG clones ranged from 33% to 79%. All contained the putative active site-containing consensus sequence pattern G-G-P-[LIVM]-x-Q-x-E-N-E-[FY] belonging to glycosyl hydrolase family 35. Six of the seven single-copy genes were mapped using restriction fragment length polymorphisms of recombinant inbred lines. RNA gel-blot analysis was used to evaluate TBG mRNA levels throughout fruit development, in different fruit tissues, and in various plant tissues. RNA gel-blot analysis was also used to reveal TBG mRNA levels in fruit of the rin, nor, and Nr tomato mutants. The TBG4-encoded protein, known to correspond to β-galactosidase II, was expressed in yeast and exo-galactanase activity was confirmed via a quantified release of galactosyl residues from cell wall fractions containing β(1→4)-d-galactan purified from tomato fruit.

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A Family of at Least Seven β-Galactosidase Genes Is Expressed during Tomato Fruit Development

Mobilisation of storage cell wall polysaccharides in seeds.

Plant glycoside hydrolases involved in cell wall polysaccharide degradation.

The main polysaccharide component of the thickened cell walls in the storage parenchyma of Lupinus angustifolius L. cotyledons is a linear (1 → 4)-β-linked d-galactan, which is mobilised after germination (L.A. Crawshaw and J.S.G Reid, 1984, Planta 160, 449–454). The isolation from the germinated cotyledons of a β-d-galactosidase or exo-(1 → 4)-β-d-galactanase with a high specificity for the lupin galactan is described. The enzyme, purified using diethylaminoethyl-cellulose, carboxymethyl-cellulose and affinity chromatography on lactose-agarose, gave two bands (major 60 kDa, minor 45 kDa) on sodium dodecyl sulphate-gel electrophoresis, and two similar bands on isoelectric focusing (major, pI 7.0, minor pI 6.7, both apparently possessing enzyme activity). The minor component cross-reacted with an antiserum raised against, and affinity-purified on, the major band. Both components had a common N-terminal sequence. The minor component was probably a degradation product of the major one. The enzyme had limited β-galactosidase action, catalysing the hydrolysis of p-nitrophenyl-β-d-galactopyranoside and (1→ 4)- and (1 → 6)-β-linked galactobioses. Lactose [β-d-galactopyranosyl-(1 → 4)-d-glucose] was hydrolysed only very slowly and methyl-β-d-galactopyranoside not at all. Lupin galactan was hydrolysed rapidly and extensively to galactose, whereas other cell-wall polysaccharides (xyloglucan and arabinogalactan) with terminal non-reducing β-d-galactopyranosyl residues were not substrates. A linear (1 → 4)-β-linked galactopentaose was hydrolysed efficiently to the tetraose plus galactose, but further sequential removals of galactose to give the tetraose and lower homologues occurred more slowly. Galactose, γ-galactonolactone and Cu+2 were inhibitory. No endo-β-d-galactanase activity was detected in lupin cotyledonary extracts, whereas exo-galactanase activity varied pari passu with galactan mobilisation. Exo-galactanase protein was detected, by Western immunoblotting of cotyledon extracts, just before the activity could be assayed and then increased and decreased in step with the enzyme activity. The exo-galactanase is clearly a key enzyme in galactan mobilisation and may be the sole activity involved in depolymerising the dominant (1 → 4)-β-galactan component of the cell wall.

Purification and properties of a novel beta-galactosidase or exo-(1-->4)-beta-D-galactanase from the cotyledons of germinated Lupinus angustifolius L. seeds.

M. S. Buckeridge

Papers

Purification and properties of a novel beta-galactosidase or exo-(1-->4)-beta-D-galactanase from the cotyledons of germinated Lupinus angustifolius L. seeds.