Crystal structures and kinetic properties of enoyl-acyl carrier protein reductase I from Candidatus Liberibacter asiaticus

Authors

  • Ling Jiang,

    1. Ministry of Education Key Laboratory of Plant Biology, Department of Horticulture and Forestry, Huazhong Agricultural University, China
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  • Zengqiang Gao,

    1. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
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  • Yanhua Li,

    1. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
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  • Shennan Wang,

    1. Ministry of Education Key Laboratory of Plant Biology, Department of Horticulture and Forestry, Huazhong Agricultural University, China
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  • Yuhui Dong

    Corresponding author
    1. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
    • Correspondence to: Y. Dong, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. E-mail: dongyh@ihep.ac.cn

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  • Ling Jiang and Zengqiang Gao contributed equally to this work.

Abstract

Huanglongbing (HLB) is a destructive citrus disease. The leading cause of HLB is Candidatus Liberibacter asiaticus. Fatty acid biosynthesis is essential for bacterial viability and has been validated as a target for the discovery of novel antibacterial agents. Enoyl−acyl carrier protein reductase (also called ENR or FabI and a product of the fabI gene) is an enzyme required in a critical step of bacterial fatty acid biosynthesis and has attracted attention as a target of novel antimicrobial agents. We determined the crystal structures of FabI from Ca. L. asiaticus in its apoform as well as in complex with b-nicotinamide adenine dinucleotide (NAD) at 1.7 and 2.7 Å resolution, respectively, to facilitate the design and screening of small molecule inhibitors of FabI. The monomeric ClFabI is highly similar to other known FabI structures as expected; however, unlike the typical tetramer, ClFabI exists as a hexamer in crystal, whereas as dimer in solution, on the other hand, the substrate binding loop which always disordered in apoform FabI structures is ordered in apo-ClFabI. Interestingly, the structure of ClFabI undergoes remarkable conformational change in the substrate-binding loop in the presence of NAD. We conclude that the signature sequence motif of FabI can be considered as Gly-(Xaa)5-Ser-(Xaa)n-Val-Tyr-(Xaa)6-Lys-(Xaa)n-Thr instead of Tyr-(Xaa)6-Lys. We have further identified isoniazid as a competitive inhibitor with NADH.

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