Prediction of a common beta-propeller catalytic domain for fructosyltransferases of different origin and substrate specificity

The three-dimensional (3D) structure of fructan biosynthetic enzymes is sti ll unknown. Here, we have explored folding similarities between reported mi crobial and plant enzymes that catalyze transfructosylation reactions. A se quence-structure compatibility search using TOPITS, SDP, 3D-PSSM, and SAM-T 98 programs identified a beta -propeller fold with scores above the confide nce threshold that indicate a structurally conserved catalytic domain in fr uctosyltransferases (FTFs) of diverse origin and substrate specificity. The predicted fold appeared related to that of neuraminidase and sialidase, of glycoside hydrolase families 33 and 34, respectively. The most reliable st ructural model was obtained using the crystal structure of neuraminidase (P rotein Data Bank file: 5nn9) as template, and it is consistent with the loc ation of previously identified functional residues of bacterial levansucras es (Batista et al., 1999; Song & Jacques, 1999). The sequence-sequence anal ysis presented here reinforces the recent inclusion of fungal and plant FTF s into glycoside hydrolase family 32, and suggests a modified sequence patt ern {H-x(2)-[PTV]-x(4)-[LIVMA]-[NSCAYG]-[DE]-P-[NDSC]-[GA]} for this family .