Insights into the potential function and membrane organization of the TP0435 (Tp17) lipoprotein from Treponema pallidum derived from structural and biophysical analyses

Abstract

The sexually transmitted disease syphilis is caused by the bacterial spirochete Treponema pallidum. This microorganism is genetically intractable, accounting for the large number of putative and undercharacterized members of the pathogen's proteome. In an effort to ascribe a function(s) to the TP0435 (Tp17) lipoprotein, we engineered a soluble variant of the protein (rTP0435) and determined its crystal structure at a resolution of 2.42 Å . The structure is characterized by an eight-stranded b-barrel protein with a shallow "basin" at one end of the barrel and an ahelix stacked on the opposite end. Furthermore, there is a disulfide-linked dimer of the protein in the asymmetric unit of the crystals. Solution hydrodynamic experiments established that purified rTP0435 is monomeric, but specifically forms the disulfide-stabilized dimer observed in the crystal structure. The data herein, when considered with previous work on TP0435, imply plausible roles for the protein in either ligand binding, treponemal membrane architecture, and/or pathogenesis.

Syphilis

“…Shown in the outer membrane are TP0751 (as known as pallilysin) 79,81 and Tpp17 (also known as TP0435) 82,241 — two surface-exposed lipoproteins; TP0453, a lipoprotein attached to the inner leaflet of the outer membrane 83 ; BamA (also known as TP0326) 84,94 ; a full-length T. pallidum repeat (Tpr) attached by its N-terminal portion to the peptidoglycan 93,94 ; and a generic β-barrel that represents other non-Tpr outer-membrane proteins identified by computational mining of the T. pallidum genome 112 . Substrates and nutrients present in high concentration in the extracellular milieu (such as, glucose) traverse the outer membrane through porins, such as TprC.…”

Treponema pallidum, the syphilis spirochete: making a living as a stealth pathogen

“…Also unclear is how, without known redox regulatory proteins (for example, OxyR, SoxR, and PerR), the bacterium senses oxidative stress, although in vitro studies indicate it has the capacity to do so 130 . The degree of disulfide bonding between TpF1 131 and Tpp17 132 monomers may serve as non-transcriptional means for redox sensing in the cytosol and periplasm, respectively.…”

Active Site Metal Identity Alters Histone Deacetylase 8 Substrate Selectivity: A Potential Novel Regulatory Mechanism

“…45 In this case, Fe(II)-LpxC has 8-fold higher activity than the zinc-bound enzyme. We would expect a similar model for metal-dependent HDACs; Fe(II)-HDAC8 ( K D 0.2 – 1 μM) 14, 46 and/or apo-HDAC8 may exist when the Zn(II) concentration is low. However, upon an increase in the exchangeable Zn(II) concentration HDAC8 could exchange the active site metal ion to form Zn(II)-HDAC 14,46 , maintaining active HDAC8 but altering the activity level and substrate selectivity.…”