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Capillary eletrophoresis is used to show that Gne catalyze the interconversion of UDP-GlcNAc/GalNAc and UDP-Glc/Gal almost equally well. The comparison of kinetic parameters of Gne from Escherichia coli O86:B7 to those of other characterized UDP-GlcNAc/Glc 4-epimerases suggests that it has relaxed specificity toward the four substrates, the first characterized enzyme to have this activity in the O-antigen biosynthesis.

Small-angle X-ray scattering (SAXS) is applied to study the conformational state and molecular properties of chain length determinant protein (Wzz) and the Wzz.O-antigen complex under near-physiological conditions. The SAXS data corresponding to Wzz and the Wzz.O-antigen complex indicate an apparent substrate (O-antigen)-induced conformational change.

Chain length determinant protein (Wzz) has been postulated to terminate the polymerization and regulate the chain length of the O-polysaccharide (0-antigen), an important component for constructing Iipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria. The investigation to understand the mechanism of Wzz has been largely slowed down due to lack of structural information. In this report, we have applied small-angle X-ray scattering (SAXS) to study the conformational state and molecular properties of Wzz and the Wzz·O-antigen complex under near-physiological conditions. No concentration- dependent aggregation or structural changes, but repulsive intermolecular interactions between Wzz molecules, are suggested in the concentration series studies. The SAXS studies suggest that Wzz protein appears to be elongated and exists as a tetramer in solution. The reconstructed model built from SAXS data indicates that the middle regime of Wzz, most likely representing the periplasmic domain, contributes to the Wzz oligomerization, which has been proposed to be correlated to the function of Wzz. The immunoblotting analyses also demonstrate that the putative coiled-coil region in the periplasmic region contributes to the oligomerization. Further, the SAXS data corresponding to Wzz and the Wzv·O-antigen complex indicate an apparent substrate (O-antigen)-induced conformational change, consistent with previous circular dichroism studies. Our finding may shed light on the biological mechanism of Wzz as a chain length determinant of 0-antigen. [ABSTRACT FROM AUTHOR]