<p>Lipopolysaccharides (LPS) are glycolipids that consitutes the outer monolayer of the outer membranes of most Gram-negative bacteria [<cite idref="PUB00028103"/>]. They consist of lipid A (endotoxin) which anchors LPS to the outer membrane, a non-repeating core oligosachharide, and an immunogenic O-antigen repeat polymer, which is an oligosaccharide of 1-40 units that variesbetween different strains of bacteria. Although the O-antigen and most of the core domain are not necessary for growth in the lab, they appear to help bacteria resist environmental stresses including the complement system and antibiotics.</p><p>This family consists of examples of ADP-L-glycero-D-mannoheptose-6-epimerase, an enzyme involved in biosynthesis of the inner core of LPS in Gram-negative bacteria [<cite idref="PUB00024627"/>]. This enzyme is homologous to UDP-glucose 4-epimerase (<db_xref db="INTERPRO" dbkey="IPR005886"/>) and belongs to the NAD dependent epimerase/dehydratase family. It participates in the biosynthetic pathway leading to incorporation of heptose, a conserved sugar, into the core region of LPS, performing the reaction shown below:<reaction>ADP-D-glycero-D-manno-heptose = ADP-L-glycero-D-manno-heptose</reaction>It is a homopentameric enzyme with each monomer composed of two domains: an N-terminal modified Rossman fold domain for NADP binding, and a C-terminal substrate binding domain.</p>