Structure of the putative thioesterase protein TTHA1846 fromThermus thermophilusHB8 complexed with coenzyme A and a zinc ion

Abstract

TTHA1846 is a conserved hypothetical protein from Thermus thermophilus HB8 with a molecular mass of 15.1 kDa that belongs to the thioesterase superfamily (Pfam 03061). Here, the 1.9 A resolution crystal structure of TTHA1846 from T. thermophilus is reported. The crystal structure is a dimer of dimers. Each subunit adopts the so-called hot-dog fold composed of five antiparallel beta-strands flanked on one side by a rather long alpha-helix and shares structural similarity to a number of thioesterases. Unexpectedly, TTHA1846 binds one metal ion and one ligand per subunit. The ligand density was modelled as coenzyme A (CoA). Its structure was confirmed by MALDI-TOF mass spectrometry and electron-density mapping. X-ray absorption fine-structure (XAFS) measurement of the crystal unambiguously characterized the metal ion as zinc. The zinc ion is tetrahedrally coordinated by the side chains of Asp18, His22 and Glu50 and the CoA thiol group. This is the first structural report of the interaction of CoA with a zinc ion. From structural and database analyses, it was speculated that the zinc ion may play an inhibitory role in the enzymatic activity.

New Insights into Coenzyme a Interaction with Mercury Ions Provided by Mass Spectrometric and Circular Dichroism Spectroscopic Approaches

“…[17][18][19] Furthermore, CoA seems to be essential for proper cellular detoxification. 20,21 Several spectroscopic and crystallographic studies have been performed in order to investigate M-CoA (M = Hg, La, Zn) complexes 20,[22][23][24] or to estimate the CoA levels in biological samples. 25 In particular, Hg 2+ can interact with CoA, via thiol sulfur and amide groups, with a 1:1 stoichiometry.…”