Structural and thermodynamic characterization of the interaction between two periplasmic Treponema pallidum lipoproteins that are components of a TPR-protein-associated TRAP transporter (TPAT)

Chad A Brautigam, Ranjit K. Deka, Peter Schuck, Diana R Tomchick, Michael V Norgard

Research output: Contribution to journalArticle

17 Scopus citations


Tripartite ATP-independent periplasmic transporters (TRAP-Ts) are bacterial transport systems that have been implicated in the import of small molecules into the cytoplasm. A newly discovered subfamily of TRAP-Ts [tetratricopeptide repeat-protein associated TRAP transporters (TPATs)] has four components. Three are common to both TRAP-Ts and TPATs: the P component, a ligand-binding protein, and a transmembrane symporter apparatus comprising the M and Q components (M and Q are sometimes fused to form a single polypeptide). TPATs are distinguished from TRAP-Ts by the presence of a unique protein called the T component. In Treponema pallidum, this protein (TatT) is a water-soluble trimer whose protomers are each perforated by a pore. Its respective P component (TatP T) interacts with the TatT in vitro and in vivo. In this work, we further characterized this interaction. Co-crystal structures of two complexes between the two proteins confirm that up to three monomers of TatP T can bind to the TatT trimer. A putative ligand-binding cleft of TatP T aligns with the pore of TatT, strongly suggesting ligand transfer between T and P T. We used a combination of site-directed mutagenesis and analytical ultracentrifugation to derive thermodynamic parameters for the interactions. These observations confirm that the observed crystallographic interface is recapitulated in solution. These results prompt a hypothesis of the molecular mechanism(s) of hydrophobic ligand transport by the TPATs.

Original languageEnglish (US)
Pages (from-to)70-86
Number of pages17
JournalJournal of Molecular Biology
Issue number1-2
Publication statusPublished - Jun 29 2012



  • protein interactions
  • syphilis
  • TPR motif
  • TRAP transporter
  • Treponema pallidum

ASJC Scopus subject areas

  • Molecular Biology

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