BIOCHEMICAL FUNCTIONAL CHARACTERIZATION AND MOLECULAR BIOLOGY OF PLANT INHIBITOR PROTEINS ACTING AGAINST GLYCOSIDE HYDROLASE
Tesi di Dottorato
Data di Pubblicazione:
2017
Citazione:
BIOCHEMICAL FUNCTIONAL CHARACTERIZATION AND MOLECULAR BIOLOGY OF PLANT INHIBITOR PROTEINS ACTING AGAINST GLYCOSIDE HYDROLASE / E. Galanti ; tutor: A. Scarafoni ; coordinatore: S. Sonnino. DIPARTIMENTO DI SCIENZE PER GLI ALIMENTI, LA NUTRIZIONE E L'AMBIENTE, 2017 Mar 07. 29. ciclo, Anno Accademico 2016. [10.13130/galanti-elisabetta_phd2017-03-07].
Abstract:
Plant cell walls are composed mostly of polysaccharides and it consist of three layers (the primary cell wall, the secondary cell wall and the middle lamella) that are made up of different percentage of cellulose, pectins and hemicelluloses. These latter are composed of a linear backbone made up of (1,4)-β-D-glycans with an equatorial configuration. Based on type of glycans forming the backbone it is possible to distinguish: mannans contain β-(1,4)-linked mannose; in xyloglucan β-1,4 glucans can be substituted with a diverse array of glycosyl and nonglycosyl residues and xylans are composed by β-(1,4)-linked xylose residues. The seeds of many legumes are known to accumulate galactomannan in their endospermic cell walls. In many dicots xyloglucans constitute the major hemicellulose of growing cell walls, comprising ~20% of the dry mass of primary cell walls. Grasses - but not monocots in general - have a reduced xyloglucan content. Cell wall polysaccharide biogenesis includes polymer synthesis, secretion, assembly, and rearrangement during development. All of these modification demands the reversible ‘loosening’ of the cellulose– hemicellulose–pectin network. Glycoside hydrolase (GH) enzymes located in the wall or in the plasma membrane play a crucial role in the degradation of different cell wall polysaccharides. On the other hand, pathogenic microorganisms secrete glycoside hydrolase to penetrate plant cell walls. As a response, plants produce glycoside hydrolase inhibitor proteins (GHIPs). Xyloglucan- specific endo-β-1,4-glucanase inhibitor proteins-like (XEGIPs-like) are typical of dicots, they inhibit the hydrolytic activity of a xyloglucan-specific β-1,4-endoglucanase isolated from GH12 family. XEGIPs-like have been found widespread in dicots: they were detected in the medium of cultured tomato cells, purified from carrot callus, isolated from the nectar of ornamental tobacco, when overexpressed they were capable of protecting potato from disease caused by endo-β-1,4- glucanase GH12 from Phytophthora infestans, enhanced in apple in response to infection of Botryosphaeria dothidea, they have distinct roles in defence mechanisms in Humulus lupus. In cereals three types of GHIPs occur in a fairly coordinated fashion throughout grain development and germination: Triticum aestivum L. endoxylanase inhibitors (TAXIs-like), xylanase inhibitor proteins (XIPs-like), thaumatin-like xylanase inhibitors (TLXIs-like). The accumulation of GHIPs during the early stages of germination is consistent with the phenomenon of germination-based resistance and their highest concentrations occur in the aleuronic layer. The apoplastic localization of GHIPs in cereals may be favourable for their action as inhibitors of microbial xylanases GH10 and/or GH11 from Aspergillus niger, Bacillus subtilis and Hypocrea jecorina intruding the host plant. GHIPs homologous are also present in legume (LACGs-like): γ-conglutin is largely expressed and accumulated in Lupinus spp. and Bg7S in Glycine spp.
GHIPs have common structural features. In particular, the alignment of the primary structurer showed that the position of the 12 cysteines is fully conserved, so various GHIPs have similar three- dimensional structures. Cys10-Cys11 is located at the C-terminal region of the proteins, the sequence amongst them is called “inhibition loop 1” and a conserved arginine, in XEGIPs-like, or leucine, in TAXI-I, is involved in the bond GH12 or GH11, respectively. In the LAGCs-like it’s also present the loop, but a deletion of about five amino acids involve this region, otherwise highly conserved. The superimposition of TAXI-I 3D structure (PDB accession number: 1T6E) and EDGP 3D structure (PDB accession number: 3VLA) with γ-conglutin 3D structure (PDB ac
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
E. Galanti
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