Poster: Cell walls

Abs # 616: Structure of Hyp-arabinogalactan polysaccharide isolated from repetitive (Ala-Hyp) expressed in Nicotiana tabacum

Presenter:	Tan, Li , lt352189@ohiou.edu
Authors	Tan, Li  (A)   Qiu, Feng  (B)   Kieliszewski, Marcia J (A)
Affiliations:	(A): Ohio University (B): Oklahoma State University

Hydroxyproline-rich glycoproteins (HRGPs) play important roles in all aspects of plant growth and development, including defense responses. Generally, HRGPs are highly O-glycosylated through the hydroxproline (Hyp) residues which means carbohydrate helps define the interactive molecular surface and therefore the function of HRGPs. The Hyp contiguity hypothesis predicts that contiguous Hyp residues are sites of HRGP arabinosylation while clustered non-contiguous Hyp residues are attachment sites of the arabinogalactan polysaccharides that characterize the arabinogalactan-proteins (AGPs). A gene encoding the repetitive sequence (AlaPro)51 was expressed in tobacco BY2 cells as enhanced green fluorescence protein (EGFP) fusion proteins. All of the Pro residues were hydroxylated and every Hyp residue was glycosylated with arabinogalactan polysaccharide, which is consistent with the hypothesis. Recently we elucidated the detailed NMR structure of the first Hyp-arabinogalactan polysaccharide, isolated from the base hydrolysates of (Ala-Hyp)51. Here, we report a second Hyp-arabinogalactan polysaccharide structure which differed from the first structure in backbone and branch lengths, and named as b-D-Galp-(1-3)-b-D-Galp-(1-3)-b-D-Galp-(1-6)-b-D-Galp-(1-3)-{[a-L-Rhap-(1-4)-b-D-GlcUA-(1-6)][(a-L-Araf-(1-3)]-b-D-Galp-(1-6)}-b-D-Galp-(1-3)-{[a-L-Rhap-(1-4)-b-D-GlcUA-(1-6)][a-L-Araf-(1-3)]-b-D-Galp-(1-6)}-b-D-Galp-(1-4)-O-Hyp. These structures confirmed the linkage between Hyp and galactose and provided the sequences of saccharides in arabinogalactan polysaccharides and arabinogalactan-proteins.