The crystal structure of HldC from B. pseudomallei (BpHldC), the fourth enzyme of the heptose bio- In previous studies, the mutant cells lacking heptoses in the inner core oligosaccharide of LPS are viable but show a deep-rough phenotype which produces outer membranes with decreased protein content and more sensitive to hydrophobic agents. 12,13 Therefore, the ADP-Lb-D-heptose biosynthesis pathway has been suggested as a good target to design novel antibiotics or antibiotic adjuvants. Burkholderia pseudomallei, a Gram-negative bacterium causing melioidosis, has been considered as a potential bioterrorism agent due to high accessibility, environmental persistence, high mortality and the lack of available vaccine 14 and exhibits extraordinary resistance to a wide range of antibiotics. 15 Therefore, intensive research for developing novel antibiotics and vaccines against melioidosis is required. The X-ray crystal structures of