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Antigenic determinants of a plant proteoglycan, the Gladiolus style arabinogalactan-protein.

ABSTRACT: Antiserum has been raised to the arabinogalactan-protein of Gladiolus style mucilage. This macromolecule has been characterized and has a structure consistent with a 1 leads to 3-linked beta-galactan backbone with side branches of 1 leads to 6-linked beta-galactosyl residues, some of which carry terminal alpha-L-arabinofuranoside residues [Gleeson & Clarke (1979) Biochem. J. 181, 607-621]. The specificity of the antiserum has been investigated by immunoprecipitation with [3H]arabinogalactan-protein. THe 3H label was introduced into the arabinogalactan-protein by oxidation of the terminal galactose residues with galactose oxidase, followed by reduction with NaB3H4. The antigenic specificity of the antiserum was shown to be directed towards the carbohydrate component of the arabinogalactan-protein. D-galactose and L-arabinose were the most effective hapten inhibitors of the antiserum; other monosaccharides, N-acetyl-D-galactono-1,4-lactone, D-glucose, D-mannose, L-rhamnose. L-fucose and D-xylose, were all poor inhibitors. The antiserum showed preference for beta-galactosides over alpha-galactosides. Of the haptens examined, the disaccharide 6-O-beta-D-galactopyranosyl-D-galactopyranose was the most potent inhibitor. The antigenic features of the arabinogalactan-protein were investigated by examining the interaction of the antiserum with chemically and enzymically modified arabinogalactan-protein. Also, the cross-reactivity of structurally related polysaccharides and glycoproteins with the specific antiserum was assessed by a haemagglutination assay using erythrocytes coupled with specific antiserum. The results indicate that the dominant antigenic determinants of the arabinogalactan-protein are probably the side branches of 1 leads to 6 -linked beta-galactose residues bearing the terminal alpha-L-arabinose residues.

SUBMITTER: Gleeson PA

PROVIDER: S-EPMC1162234 | biostudies-other | 1980 Nov

REPOSITORIES: biostudies-other

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Project description:BackgroundPollen tube growth and fertilization are key processes in angiosperm sexual reproduction. The transmitting tract (TT) of Nicotiana tabacum controls pollen tube growth in part by secreting pistil extensin-like protein III (PELPIII), transmitting-tract-specific (TTS) protein and 120 kDa glycoprotein (120 K) into the stylar extracellular matrix. The three arabinogalactan proteins (AGP) are referred to as stylar AGPs and are the focus of this research. The transmitting tract regulates pollen tube growth, promoting fertilization or rejecting pollen tubes.ResultsThe N-terminal domain (NTD) of the stylar AGPs is proline rich and polymorphic among Nicotiana spp. The NTD was predicted to be mainly an intrinsically disordered region (IDR), making it a candidate for protein-protein interactions. The NTD is also the location for the majority of the predicted O-glycosylation sites that were variable among Nicotiana spp. The C-terminal domain (CTD) contains an Ole e 1-like domain, that was predicted to form beta-sheets that are similar in position and length among Nicotiana spp. and among stylar AGPs. The TTS protein had the greatest amino acid and predicted O-glycosylation conservation among Nicotiana spp. relative to the PELPIII and 120 K. The PELPIII, TTS and 120 K genes undergo negative selection, with dn/ds ratios of 0.59, 0.29 and 0.38 respectively. The dn/ds ratio for individual species ranged from 0.4 to 0.9 and from 0.1 to 0.8, for PELPIII and TTS genes, respectively. These data indicate that PELPIII and TTS genes are under different selective pressures. A newly discovered AGP gene, Nicotiana tabacum Proline Rich Protein (NtPRP), was found with a similar intron-exon configuration and protein structure resembling other stylar AGPs, particularly TTS.ConclusionsFurther studies of the NtPRP gene are necessary to elucidate its biological role. Due to its high similarity to the TTS gene, NtPRP may be involved in pollen tube guidance and growth. In contrast to TTS, both PELPIII and 120 K genes are more diverse indicating a possible role in speciation or mating preference of Nicotiana spp. We hypothesize that the stylar AGPs and NtPRP share a common origin from a single gene that duplicated and diversified into four distinct genes involved in pollen-style interactions.

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Antigenic determinants of a plant proteoglycan, the Gladiolus style arabinogalactan-protein.

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