Binding interactions between barley thaumatin-like proteins and (1,3)-beta-D-glucans. Kinetics, specificity, structural analysis and biological implications.
The specificity and kinetics of the interaction between the pathogenesis-related group of thaumatin-like proteins (PR5) in higher plants and (1,3)-beta-D-glucans have been investigated. Two thaumatin-like proteins with 60% amino-acid sequence identity were purified from extracts of germinated barley grain, and were designated HvPR5b and HvPR5c. Purified HvPR5c interacted with insoluble (1,3)-beta-D-glucans, but not with cellulose, pustulan, xylan, chitin or a yeast mannoprotein. Tight binding was observed with unbranched and unsubstituted (1,3)-beta-D-glucans, and weaker binding was seen if (1,6)-beta-linked branch points or beta-glucosyl substituents were present in the substrate. The HvPR5b protein interacted weakly with insoluble (1,3)-beta-D-glucans and did not bind to any of the other polysaccharides tested. This indicated that only specific barley PR5 isoforms interact tightly with (1,3)-beta-D-glucans. The complete primary structures of HvPR5b and HvPR5c were determined and used to construct molecular models of HvPR5b and HvPR5c, based on known three-dimensional structures of related thaumatin-like proteins. The models were examined for features that may be associated with (1,3)-beta-D-glucan binding, and a potential (1,3)-beta-D-glucan-binding region was located on the surface of HvPR5c. No obvious structural features that would prevent binding of (1,3)-beta-D-glucan to HvPR5b were identified, but several of the amino acids in HvPR5c that are likely to interact with (1,3)-beta-D-glucans are not present in HvPR5b.
Osmond
R I
RI
The Department of Plant Science, University of Adelaide, Glen Osmond, Australia.
Hrmova
M
M
Fontaine
F
F
Imberty
A
A
Fincher
G B
GB
D000327:Adsorption; D000595:Amino Acid Sequence; D001665:Binding Sites; D018076:DNA, Complementary / Q000378:metabolism; D005936:Glucans / Q000737:chemistry* / Q000378:metabolism; D001467:Hordeum / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D013549:Sweetening Agents; D013997:Time Factors; D047071:beta-Glucans
D018076:DNA, Complementary; D005936:Glucans; D010940:Plant Proteins; D011134:Polysaccharides; D013549:Sweetening Agents; D047071:beta-Glucans; C003427:thaumatin protein, plant; C033363:beta-1,3-glucan