A coiled-coil domain acts as a molecular ruler to regulate O-antigen chain length in lipopolysaccharide
A coiled-coil domain acts as a molecular ruler to regulate O-antigen chain length in lipopolysaccharide
Hagelueken, G., et al. Nature structural & molecular biology 22, 50-56 (2015)
Speaker: Jui-Chieh Yin (尹睿婕) Time: 14:10~15:00, Apr.15, 2015
Commentator: Dr. Shang-Rung Wu (吳尚蓉老師) Place: Room 601
Abstract
Lipopolysaccharide (LPS) is major component of the outer membrane in most Gram-negative bacteria. LPS is also known as endotoxin and composed of lipid A, core oligosaccharide andantigenic O-antigen polysaccharide (O-PS). O-PS is associated with virulence, and there are over 180 O-antigen serogroups found in Escherichia coli1. The O-PS of E. coli O9a is exported by the ATP-binding cassette transporter-dependent pathway with interactions of multiple proteins. The length of the O9a O-PS is determined by WbdA and WbdD. In addition, WbdD contains kinase andmethyltransferase domain and terminates polymerization of O-PS2. However, the mechanism of length determination of O-PS chain is still unclear. Therefore, the authors combined X-ray crystallography and small-angle X-ray scattering (SAXS) to investigate the assembly of O-PS in E. coli O9a. Crystallographic data were collected for Wbd1-556 showed that the C-terminus ofWbdD contained a coiled-coil domain. Furthermore, the coiled-coil domain interacts with the kinase active site resulting in two active site loops interaction with each other between W408 and W382. Moreover, the authors modeled the missing structure of coiled-coil domain at the N-terminus of WbdD. The model of coiled-coil domain in Wbd1-556 structure is rectified and validated with the SAXS data. Furthermore, they designed four constructs which were either deleting consecutive heptads or inserting additional blocks of heptads in coiled-coil domain to elucidate the structural basis of of O-PS synthesis by WbdD. LPS with deletion residues caused shorter O-PS chain length than wild-type by deletion and vice versa. Taken together, this work combined X-ray crystallography and SAXS to reveal the atomic structure of coiled-coil domain in WbdD and discovered the coiled-coil domain of WbdD plays a role as molecular ruler during O-PS synthesis in E. coli O9a. This discovery provides insights into molecular ruler and it may be modified to design a novel drug against enteric disease.
References
1. Hagelueken, G., et al. Structure of WbdD: a bifunctional kinase and methyltransferase that regulates the chain length of the O antigen in Escherichia coli O9a. Molecular microbiology 86, 730-742 (2012).
2. King, J.D., et al. Lipopolysaccharide O antigen size distribution is determined by a chain extension complex of variable stoichiometry in Escherichia coli O9a. Proceedings of the National Academy of Sciences of the United States of America 111, 6407-6412 (2014).