2IU9

Structure and Reactivity of Lpxd, the N-Acyltransferase of Lipid a Biosynthesis

(2007) Proc Natl Acad Sci U S A 104: 4321

• PubMed: 17360522 Search on PubMedSearch on PubMed Central
• DOI: https://doi.org/10.1073/pnas.0606356104
• Primary Citation of Related Structures:  
  2IU8, 2IU9, 2IUA


• PubMed Abstract: 
  

  The external layer of the Gram-negative bacterial outer membrane is primarily composed of a protective, selectively permeable LPS. The biosynthesis of LPS relies on UDP-3-O-acyl-glucosamine N-acyltransferase (LpxD), which transfers 3-hydroxy-arachidic acid from acyl carrier protein to the 2' amine of UDP-3-O-myristoyl glucosamine in Chlamydia trachomatis. Our crystallographic study reveals that LpxD is a homotrimer, each subunit of which is constructed from a novel combination of an N-terminal uridine-binding domain, a core lipid-binding domain, and a C-terminal helical extension. Highly conserved residues dominate nucleotide binding. Phe-43 and Tyr-49 form pi-stacking interactions with uracil, and Asn-46 and His-284 form hydrogen bonds with the phosphate groups. These interactions place the glucosamine moiety at the catalytic center formed by two adjacent subunits. Here His-247 and His-284 contribute to a mechanism involving nucleophilic attack by the amine of one substrate on the carbonyl carbon of an acyl carrier protein thioester conjugate. Serendipitously, our study reveals a fatty acid (FA) binding groove near the catalytic center. MS elucidated the presence of a FA mixture binding to LpxD, with palmitic acid the most prevalent. The placement of UDP-N-acetylglucosamine and the FA provides details of N-acyltransferase ligand interactions and allows for a description of structure and reactivity at an early stage of LPS assembly.

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Organizational Affiliation: 

Division of Biological Chemistry and Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.