TY - JOUR
T1 - Substrate preference of an ABC importer corresponds to selective growth on β-(1,6)-galactosides in Bifidobacterium animalis subsp. lactis
AU - Theilmann, Mia Christine
AU - Fredslund, Folmer
AU - Svensson, Birte
AU - Lo Leggio, Leila
AU - Abou Hachem, Maher
PY - 2019/8/2
Y1 - 2019/8/2
N2 - Bifidobacteria are exposed to substantial amounts of dietary-galactosides. Distinctive preferences for growth on different-galactosides are observed within Bifidobacterium members, but the basis of these preferences remains unclear. We previously described the first -(1,6)/(1,3)-galactosidase from Bifidobacterium animalis subsp. lactis Bl-04. This enzyme is relatively promiscuous, exhibiting only 5-fold higher efficiency on the preferred -(1,6)-galactobiose than the -(1,4) isomer. Here, we characterize the solute-binding protein (Bal6GBP) that governs the specificity of the ABC transporter encoded by the same-galactoside utilization locus. We observed that although Bal6GBP recognizes both -(1,6)- and -(1,4)-galactobiose, Bal6GBP has a 1630-fold higher selectivity for the former, reflected in dramatic differences in growth, with several hours lag on less preferred -(1,4)- and -(1,3)-galactobiose. Experiments performed in the presence of varying proportions of -(1,4)/-(1,6)-galactobioses indicated that the preferred substrate was preferentially depleted from the culture supernatant. This established that the poor growth on the nonpreferred -(1,4) was due to inefficient uptake. We solved the structure of Bal6GBP in complex with -(1,6)-galactobiose at 1.39 Å resolution, revealing the structural basis of this strict selectivity. Moreover, we observed a close evolutionary relationship with the human milk disaccharide lacto-N-biose-binding protein from Bifidobacterium longum, indicating that the recognition of the nonreducing galactosyl is essentially conserved, whereas the adjacent position is diversified to fit different glycosidic linkages and monosaccharide residues. These findings indicate that oligosaccharide uptake has a pivotal role in governing selectivity for distinct growth substrates and have uncovered evolutionary trajectories that shape the diversification of sugar uptake proteins within Bifidobacterium.
AB - Bifidobacteria are exposed to substantial amounts of dietary-galactosides. Distinctive preferences for growth on different-galactosides are observed within Bifidobacterium members, but the basis of these preferences remains unclear. We previously described the first -(1,6)/(1,3)-galactosidase from Bifidobacterium animalis subsp. lactis Bl-04. This enzyme is relatively promiscuous, exhibiting only 5-fold higher efficiency on the preferred -(1,6)-galactobiose than the -(1,4) isomer. Here, we characterize the solute-binding protein (Bal6GBP) that governs the specificity of the ABC transporter encoded by the same-galactoside utilization locus. We observed that although Bal6GBP recognizes both -(1,6)- and -(1,4)-galactobiose, Bal6GBP has a 1630-fold higher selectivity for the former, reflected in dramatic differences in growth, with several hours lag on less preferred -(1,4)- and -(1,3)-galactobiose. Experiments performed in the presence of varying proportions of -(1,4)/-(1,6)-galactobioses indicated that the preferred substrate was preferentially depleted from the culture supernatant. This established that the poor growth on the nonpreferred -(1,4) was due to inefficient uptake. We solved the structure of Bal6GBP in complex with -(1,6)-galactobiose at 1.39 Å resolution, revealing the structural basis of this strict selectivity. Moreover, we observed a close evolutionary relationship with the human milk disaccharide lacto-N-biose-binding protein from Bifidobacterium longum, indicating that the recognition of the nonreducing galactosyl is essentially conserved, whereas the adjacent position is diversified to fit different glycosidic linkages and monosaccharide residues. These findings indicate that oligosaccharide uptake has a pivotal role in governing selectivity for distinct growth substrates and have uncovered evolutionary trajectories that shape the diversification of sugar uptake proteins within Bifidobacterium.
U2 - 10.1074/jbc.ra119.008843
DO - 10.1074/jbc.ra119.008843
M3 - Journal article
C2 - 31186348
SN - 0021-9258
VL - 294
SP - 11701
EP - 11711
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 31
ER -