Rhamnoarabinosyl and rhamnoarabinoarabinosyl side chains as structural features of coffee arabinogalactans.
The hot water soluble green coffee arabinogalactans, representing nearly 7% of total coffee bean arabinogalactans, were characterized by (1)H and (13)C NMR and, after partial acid hydrolysis, by ESI-MS/MS. Data obtained showed that these are highly branched type II arabinogalactans covalently linked to proteins (AGP), with a protein moiety containing 10% of 4-hydroxyproline residues. They possess a beta-(1-->3)-Galp/beta-(1-->3,6)-Galp ratio of 0.80, with a sugars composition of Rha:Ara:Gal of 0.25:1.0:1.5, and containing 2mol% of glucuronic acid residues. Beyond the occurrence of single alpha-L-Araf residues and [alpha-L-Araf-(1-->5)-alpha-L-Araf-(1-->] disaccharide residues as side chains, these AGPs contain unusual side chains at O-3 position of the beta-(1-->6)-linked galactopyranosyl residues composed by [alpha-L-Rhap-(1-->5)-alpha-L-Araf-(1-->] and [alpha-L-Rhap-(1-->5)-alpha-L-Araf-(1-->5)-alpha-L-Araf-(1-->] oligosaccharides. Rhamnoarabinosyl and rhamnoarabinoarabinosyl side chains are reported for the first time as structural features of plant arabinogalactan-proteins.
Nunes
Fernando M
FM
Departamento de Química, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal. fnunes@utad.pt
Reis
Ana
A
Silva
Artur M S
AM
Domingues
M Rosário M
MR
Coimbra
Manuel A
MA
D003069:Coffee / Q000737:chemistry*; D005685:Galactans / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D015394:Molecular Structure; D009844:Oligosaccharides / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry*
D003069:Coffee; D005685:Galactans; D009844:Oligosaccharides; D011134:Polysaccharides; C005653:arabinogalactan