National Center for
5AY9: Crystal Structure Of Ruminococcus Albus 4-o-beta-d-mannosyl-d-glucose Phosphorylase (ramp1)
Structural insights into the difference in substrate recognition of two mannoside phosphorylases from two GH130 subfamilies
FEBS Lett. (2016) 590 p.828-837
In Ruminococcus albus, 4-O-beta-d-mannosyl-d-glucose phosphorylase (RaMP1) and beta-(1,4)-mannooligosaccharide phosphorylase (RaMP2) belong to two subfamilies of glycoside hydrolase family 130. The two enzymes phosphorolyze beta-mannosidic linkages at the nonreducing ends of their substrates, and have substantially diverse substrate specificity. The differences in their mechanism of substrate binding have not yet been fully clarified. In the present study, we report the crystal structures of RaMP1 with/without 4-O-beta-d-mannosyl-d-glucose and RaMP2 with/without beta-(1-->4)-mannobiose. The structures of the two enzymes differ at the +1 subsite of the substrate-binding pocket. Three loops are proposed to determine the different substrate specificities. One of these loops is contributed from the adjacent molecule of the oligomer structure. In RaMP1, His245 of loop 3 forms a hydrogen-bond network with the substrate through a water molecule, and is indispensible for substrate binding.