Evidence for posttranslational protein flavinylation in the syphilis spirochete Treponema pallidum: Structural and biochemical insights from the catalytic core of a periplasmic flavin-trafficking protein
- The University of Texas Southwestern Medical Center, Dallas, TX (United States)
The syphilis spirochete Treponema pallidum is an important human pathogen but a highly enigmatic bacterium that cannot be cultivated in vitro. T. pallidum lacks many biosynthetic pathways and therefore has evolved the capability to exploit host-derived metabolites via its periplasmic lipoprotein repertoire. We recently reported a flavin-trafficking protein in T. pallidum (Ftp_Tp; TP0796) as the first bacterial metal-dependent flavin adenine dinucleotide (FAD) pyrophosphatase that hydrolyzes FAD into AMP and flavin mononucleotide (FMN) in the spirochete’s periplasm. However, orthologs of Ftp_Tp from other bacteria appear to lack this hydrolytic activity; rather, they bind and flavinylate subunits of a cytoplasmic membrane redox system (Nqr/Rnf). To further explore this dichotomy, biochemical analyses, protein crystallography, and structure-based mutagenesis were used to show that a single amino acid change (N55Y) in Ftp_Tp converts it from an Mg²⁺-dependent FAD pyrophosphatase to an FAD-binding protein. We also demonstrated that Ftp_Tp has a second enzymatic activity (Mg²⁺-FMN transferase); it flavinylates protein(s) covalently with FMN on a threonine side chain of an appropriate sequence motif using FAD as the substrate. Moreover, mutation of a metal-binding residue (D284A) eliminates Ftp_Tp’s dual activities, thereby underscoring the role of Mg²⁺ in the enzyme-catalyzed reactions. The posttranslational flavinylation activity that can target a periplasmic lipoprotein (TP0171) has not previously been described. The observed activities reveal the catalytic flexibility of a treponemal protein to perform multiple functions. Together, these findings imply mechanisms by which a dynamic pool of flavin cofactor is maintained and how flavoproteins are generated by Ftp_Tp locally in the T. pallidum periplasm.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER); National Institutes of Health (NIH)
- Grant/Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1214713
- Journal Information:
- mBio (Online), Vol. 6, Issue 3; ISSN 2150-7511
- Publisher:
- American Society for MicrobiologyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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