Molecular evolution of plant β‐glucan endohydrolases

Abstract

now present opportunities to explore the precise molecular and atomic details of substrata-binding, catalytic mechanisms and the sequence of molecular events that resulted in the evolution of the substrata specificities of the two classes of enzyme. SummaryThe evolutionary relationships of two classes of plant ~-glucan endohydroleses have been examined by comparison of their substrata specificities, their three-dimensional conformations and the structural features of their corresponding genes. These comparative studies provide compelling evidence that the (1-~3)-~-glucaneses and (l~3,1~4)-~-glucaneses from higher plants share a common ancestry and, in all likelihood, that the (l~3,1~4)-~-glucaneses diverged from the (l~3)-~-glucaneses during the appearance of the graminaceous monocotyledons. The evolution of (1-~3,1~4)-~-glucaneses from (1-~3)-~-glucaneses does not appear to have invoked 'modular' mechanisms of change, such as those caused by exon shuffling or recombination. Instead, the shift in specificity has been acquired through a limited number of point mutations that have resulted in amino acid substitutions along the substrate-binding cleft. This is consistent with current theories that the evolution of new enzymic activity is often achieved through duplication of the gene encoding an existing enzyme which is capable of performing the required chemistry, in this case the hydrolysis of a glycosidic linkage, followed by the mutational alteration and fine-tuning of substrate specificity.The evolution of a new specificity has enabled a dramatic shift in the functional capabilities of the enzymes. (1-~3)-~-Glucanases that play a major role, inter alia, in the protection of the plant against pathogenic microorganisms through their ability to hydrolyse the (l---~3)-~-glucans of fungal cell walls, appear to have been recruited to generate (1-~3,1-~4)-13-glucaneses, which quite specifically hydrolyse plant cell wall (l~3,1-~4)-~-glucans in the graminaecous monocotyledons during normal wall metabolism. Thus, one class of J3-glucan endohydrolese can degrade ~-glucans in fungal walls, while the other hydrolyses structurally distinct ~-glucans of plant cell walls. Detailed information on the three-dimensional structures of the enzymes and the identification of catalytic amino acids

Ole e 9, a Major Olive Pollen Allergen Is a 1,3-β-Glucanase

“…Although many 1,3-␤-glucanases have been described as PR proteins because of their induction by pathogens, others have been found to be constitutive enzymes (PR-like proteins) expressed during physiological and developmental processes of healthy plants, such as germination, senescence, fertilization, and responses to environmen- tal conditions (55,58,60,61). Based on the length of the polypeptide chain, two types of 1,3-␤-glucanases have been described: 1) short 1,3-␤-glucanases, which exhibit basic or acidic pI, and molecular masses comprised between 33 and 41 kDa (300 -350 amino acids) and 2) long 1,3-␤-glucanases with molecular masses of ϳ45 kDa (420 -480 amino acid residues) and being moderately acidic (1,3-␤-glucanase from wheat Alintoxicated roots (56)) or basic (A6 proteins from A. thaliana and rapeseed anthers (36) and SgGN1 from willow male catkins (38)).…”

Glycoside Hydrolases in Plant Cell Wall Proteomes: Predicting Functions That Could Be Relevant for Improving Biomass Transformation Processes

“…Noteworthy, β-1,3-glucanases can accumulate in vacuoles of root cells or mature leaf cells in response to pathogen infection, whereas others are secreted to the extracellular space, but they can also be secreted in the absence of pathogen infection [55]. They are, thus, also important during plant development, being involved in cell division, pollen development, seed germination, and maturation as well as in signaling [55,59,60].…”

Plant Allergens and Pathogenesis-Related Proteins

“…These enzymes catalyse endo-type hydrolytic cleavage of the 1,3-β- D -glucosidic linkages in β-1,3-glucans, the abundant component of plant cell walls. The β-1,3-glucanases are highly regulated enzymes, especially in seed-plant species [6]. These enzymes are thought to play a role in response of plants to microbial pathogens, but it is also evident that they are implicated in a number of physiological and developmental processes in uninfected plants, like pollen germination and tube growth, fertilisation, fruit ripening, seed germination, mobilisation of storage products in the endosperm of cereal grains [7, 8]and last but not least they represent a response to wounding, cold, ozone, and UV-B [8].…”