Crystal structure of SsfS6, the putative C‐glycosyltransferase involved in SF2575 biosynthesis

Abstract

The molecule known as SF2575 from Streptomyces sp. is a tetracycline polyketide natural product that displays antitumor activity against murine leukemia P388 in vivo. In the SF2575 biosynthetic pathway, SsfS6 has been implicated as the crucial C-glycosyltransferase (C-GT) that forms the C-C glycosidic bond between the sugar and the SF2575 tetracycline-like scaffold. Here, we report the crystal structure of SsfS6 in the free form and in complex with TDP, both at 2.4 Å resolution. The structures reveal SsfS6 to adopt a GT-B fold wherein the TDP and docked putative aglycon are consistent with the overall C-glycosylation reaction. As one of only a few existing structures for C-glycosyltransferases, the structures described herein may serve as a guide to better understand and engineer C-glycosylation.

The C-glycosyltransferase IroB from pathogenic Escherichia coli: Identification of residues required for efficient catalysis

“…3b) exhibits a two-domain GT-B fold characteristic of C-glycosyltransferases of known structure. 19,20 The 279-WVPQ-282 was found to structurally align with IroB residues 264-WIPM-267 ( Fig. 3c).…”

“…2P6P) 19 and the C-glycosyltransferase SsfS6 from Streptomyces sp. (PDB code: 4G2T) 20 as the C-GT orthologues with the highest degree of structural alignment. We therefore used 2P6P and 4G2T as templates for homology modeling using Modeller v9.…”

A comprehensive review of glycosylated bacterial natural products

“…314 The structural elucidation of the TAN-X C -glycosyltransferase SsfS6 was recently reported as one among only a few C -glycosyltransferases to be structurally characterized to date. 322 …”

Structural Characterization of O‐ and C‐Glycosylating Variants of the Landomycin Glycosyltransferase LanGT2

“…[14] On the side of the base distal from W267, the side chain of L270 is situated above the base, in a motif that is typically observed in TDP-sugar-utilizing GTs, such as GtfA, CalG3, SpnG, and SsfS6 (Figure 3B). [14,15] H283 in LanGT2 and LanGT2-S8Ac is conserved throughout the GT-1 family and has been proposed to stabilize the accumulation of charge on the phosphate during catalysis. [16] Additionally, the negative charges of the central pyrophosphate of the ligand are compensated by positioning this part of the molecule at the positively charged end of helix h 10 of the enzyme.…”