Structure and ligand binding of the soluble domain of a Thermotoga maritima membrane protein of unknown function TM1634.

As a part of the Joint Center for Structural Genomics (JCSG) biological targets, the structures of soluble domains of membrane proteins from Thermotoga maritima were pursued. Here, we report the crystal structure of the soluble domain of TM1634, a putative membrane protein of 128 residues (15.1 kDa) and unknown function. The soluble domain of TM1634 is an alpha-helical dimer that contains a single tetratrico peptide repeat (TPR) motif in each monomer where each motif is similar to that found in Tom20. The overall fold, however, is unique and a DALI search does not identify similar folds beyond the 38-residue TPR motif. Two different putative ligand binding sites, in which PEG200 and Co(2+) were located, were identified using crystallography and NMR, respectively.