Crystallographic analysis of NosA, which catalyzes terminal amide formation in the biosynthesis of nosiheptide

Nosiheptide is a member of the thiopeptide family of antibiotics which demonstrates potent activities against various bacterial pathogens. The formation of its C-terminal amide is catalysed by NosA in an unusual strategy for maturating certain thiopeptides by processing precursor peptides featuring a serine extension. Here, a recombinant C-terminally truncated selenomethionine-derivatized NosA1–111variant fromStreptomyces actuosusconsisting of residues 1–111, named SeMet NosA1–111, was crystallized using the sitting-drop vapour-diffusion method. Diffraction data were collected to 2.40 Å resolution using synchrotron radiation. The crystals belonged to the primitive cubic space groupP4132, with unit-cell parametersa=b=c= 143.3 Å. Assuming the presence of three molecules in the asymmetric unit, the calculated Matthews coefficient was 3.94 Å3 Da−1and the corresponding solvent content was 40.3%.