Enzymatic hydrolysis studies of arabinogalactan-protein structure from Acacia gum: The self-similarity hypothesis of assembly from a common building block

•AG molecular fraction from Acacia gum is unaffected by acidic and alkaline proteases.•AGP molecular fraction from Acacia gum is affected only by alkaline proteases.•Conformations of enzyme-treated AGPs are very similar and close to AG.•Self-ordering process governs AGP macromolecular assembly. Arab...

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Bibliographic Details
Published in:Carbohydrate polymers 2014-11, Vol.112, p.648-661
Main Authors: Renard, D., Lavenant-Gourgeon, L., Lapp, A., Nigen, M., Sanchez, C.
Format: Article
Language:English
Subjects:
Acacia gum
Applied sciences
Arabinogalactan-protein
Chromatography, Gel - methods
Circular Dichroism
Enzymes - chemistry
Enzymes - metabolism
Exact sciences and technology
Galactans - chemistry
Gum Arabic - chemistry
HPSEC-MALLS
Hydrogen-Ion Concentration
Hydrolysis
Life Sciences
Mucoproteins - chemistry
Mucoproteins - metabolism
Natural polymers
Physicochemistry of polymers
Plant Proteins - chemistry
Plant Proteins - metabolism
Scattering, Small Angle
Self-ordering
Small-angle neutron scattering
Starch and polysaccharides
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Summary:•AG molecular fraction from Acacia gum is unaffected by acidic and alkaline proteases.•AGP molecular fraction from Acacia gum is affected only by alkaline proteases.•Conformations of enzyme-treated AGPs are very similar and close to AG.•Self-ordering process governs AGP macromolecular assembly. Arabinogalactan (AG) and arabinogalactan-protein (AGP) fractions were treated enzymatically using several proteases in acidic (pH 4) and alkaline (pH 7) conditions in order to go deeper insight into the structure and conformations of the two main fractions of Acacia senegal gum. Endoproteinase Glu-C, pepsin and phosphatase acid were thus used in acidic conditions while subtilisin A, pronase, trypsin, papain and proteinase K were used in alkaline conditions to cleave protein moieties of the two fractions. Structures of AG and AGP were probed using HPSEC-MALLS, small angle neutron scattering and far-UV circular dichroism. Enzymes did not affect AG fraction structure whatever the pH conditions used, highlighting the inaccessibility of the peptide backbone and the remarkable stability of this fraction in acidic and alkaline conditions. This result was in agreement with the thin oblate ellipsoid model we previously identified for the AG fraction where the 43 amino-acid residues peptide sequence was supposed, based on spectroscopic methods, to be totally buried. Contrary to AG fraction, AGP protein component was therefore cleaved using enzymes in alkaline conditions, the absence of enzymatic efficiency in acidic conditions being probably ascribed to long range electrostatic repulsions occurring between negatively charged AGP and enzymes at pH 4. The decrease of AGP molecular weight after hydrolysis in alkaline conditions went from 1.79×106gmol−1 for control AGP to as low as 1.68×105gmol−1 for papain-treated AGP. The overall structure of the enzyme-treated AGPs was found to be surprisingly quite similar whatever the enzyme used and close, with however some subtle differences, to AG unit. A tri-axial ellipsoid conformation was found in enzyme-treated AGPs and the two main preferential distances identified in the pair distance distribution function would claim in favor of rod-like or elongated particles or alternatively would indicate the presence of two particles differing in dimensions. The secondary structures content of control and enzyme-treated AGPs were similar, highlighting both the high rigidity of the protein backbone and the overall symmetry of AGP. This conclusio
ISSN:0144-8617
1879-1344
DOI:10.1016/j.carbpol.2014.06.041