Epsilon glutathione transferases possess a unique class-conserved subunit interface motif that directly interacts with glutathione in the active site

Analysis of a new structure of an Epsilon class glutathione transferase from Drosophila melanogaster reveals a highly conserved motif that spans the dimeric subunit interface and connects the two active sites.

Assaying the kinetics of protein denaturation catalyzed by AAA+ unfolding machines and proteases

ATP-dependent molecular machines of the AAA+ superfamily unfold or remodel proteins in all cells. For example, AAA+ ClpX and ClpA hexamers collaborate with the self-compartmentalized ClpP peptidase to unfold and degrade specific proteins in bacteria and some eukaryotic organelles. Although degradation assays are straightforward, robust methods to assay the kinetics of enzyme-catalyzed protein unfolding in the absence of proteolysis have been lacking. Here, we describe a FRET-based assay in which enzymatic unfolding converts a mixture of donor-labeled and acceptor-labeled homodimers into heterodimers. In this assay, ClpX is a more efficient protein-unfolding machine than ClpA both kinetically and in terms of ATP consumed. However, ClpP enhances the mechanical activities of ClpA substantially, and ClpAP degrades the dimeric substrate faster than ClpXP. When ClpXP or ClpAP engage the dimeric subunit, one subunit is actively unfolded and degraded, whereas the other subunit is passively unfolded by loss of its partner and released. This assay should be broadly applicable for studying the mechanisms of AAA+ proteases and remodeling chaperones.

2-Hexanoyl-1-tribromomethyl-1,2,3,4-tetrahydro-β-carboline: Crystal Structure Analysis of a Potent Inhibitor of Complex I of Mitochondrial Respiration

The molecular structure of the title compound 2-hexanoyl-1-tribromomethyl-1,2,3,4-tetra-hydro-β-carboline (3), a potent inhibitor of complex I of the mammalian mitochondrial respiratory chain, has been studied by single-crystal X-ray diffraction analysis. In the crystal, two heterochiral molecules of 3 (i.e., one R- and one S-configured molecule each) were found to be connected with one other in pairs via two intermolecular hydrogen bonds [O(215) ··· H(212)′ and O(215)′ ··· H(212)] to form an overall achiral ‘dimeric’ subunit