Structural and Thermodynamic Characterization of the Interaction between Two Periplasmic Treponema pallidum Lipoproteins that are Components of a TPR-Protein-Associated TRAP Transporter (TPAT)

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• 作者：Chad A. Brautigam¹ ; ^&dagger ; ; Ranjit K. Deka² ; ^&dagger ; ; Peter Schuck³ ; Diana R. Tomchick¹ ; Michael V. Norgard² ; ^{Michael.Norgard@UTSouthwestern.edu}
• 关键词：TPAT ; tetratricopeptide repeat-protein associated TRAP transporter ; TRAP-T ; tripartite ATP-independent periplasmic transporter ; OM ; outer membrane ; IM ; inner membrane ; SBP ; substrate-binding protein ; cTPR ; cryptic tetratricopeptide repeat ; CF ; cleft finge
• 刊名：Journal of Molecular Biology
• 出版年：2012
• 期刊代码：102_00222836
• 类别：imm
• 出版时间：29 June, 2012
• 卷：420
• 期：1-2
• 页码：70-86
• 文件大小：2419 K

摘要

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 鈥淭 component鈥? 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.