NifS-like proteins are ubiquitous, homodimeric, proteins which belong to the alpha-family of pyridoxal-5'-phoshate dependent enzymes. They are proposed to donate elementary sulphur, generated from cysteine, via a cysteinepersulphide intermediate during iron sulphur cluster biosynthesis, an important albeit not well understood process. Here, we report on the crystal structure of a NifS-like protein from the hyperthermophilic bacterium Thermotoga maritima (tmNifS) at 2.0 A resolution. The tmNifS is structured into two domains, the larger bearing the pyridoxal-5'-phosphate-binding active site, the smaller hosting the active site cysteine in the middle of a highly flexible loop, 12 amino acid residues in length. Once charged with sulphur the loop could possibly deliver S(0) directly to regions far remote from the protein. Based on the three-dimensional structures of the native as well as the substrate complexed form and on spectrophotometric results, a mechanism of sulphur activation is proposed. The His99, which stacks on top of the pyridoxal-5'-phosphate co-factor, is assigned a crucial role during the catalytic cycle by acting as an acid-base catalyst and is believed to have a pK(a) value depending on the co-factor redox state.
PDB ID: 1EG5Download
MMDB ID: 12892
PDB Deposition Date: 2000/2/13
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 1EG5: dimeric; determined by author and by software (PISA)
Molecular Components in 1EG5
Label Count Molecule
Proteins (2 molecules)
Molecule annotation
Chemicals (4 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB