Three-dimensional structure of Serratia marcescens nuclease at 1.7 Å resolution and mechanism of its action

AbstractThe three-dimensional crystal structure of Serratia marcescens (Sm) nuclease has been refined at 1.7 Å resolution to the R-factor of 17.3% and R-free of 22.2%. The final model consists of 3678 non-hydrogen atoms and 443 water molecules. The analysis of the secondary and the tertiary structures of the Sm nuclease suggests a topology which reveals essential inner symmetry in all the three layers forming the monomer. We propose the plausible mechanism of its action based on a concerted participation of the catalytically important amino acid residues of the enzyme active site

Expression of soluble, active fragments of the morphogenetic protein SpoIIE from Bacillus subtilis using a library-based construct screen

SpoIIE is a dual function protein that plays important roles during sporulation in Bacillus subtilis. It binds to the tubulin-like protein FtsZ causing the cell division septum to relocate from mid-cell to the cell pole, and it dephosphorylates SpoIIAA phosphate leading to establishment of differential gene expression in the two compartments following the asymmetric septation. Its 872 residue polypeptide contains a multiple-membrane spanning sequence at the N-terminus and a PP2C phosphatase domain at the C-terminus. The central segment that binds to FtsZ is unlike domains of known structure or function, moreover the domain boundaries are poorly defined and this has hampered the expression of soluble fragments of SpoIIE at the levels required for structural studies. Here we have screened over 9000 genetic constructs of spoIIE using a random incremental truncation library approach, ESPRIT, to identify a number of soluble C-terminal fragments of SpoIIE that were aligned with the protein sequence to map putative domains and domain boundaries. The expression and purification of three fragments were optimised, yielding multimilligram quantities of the PP2C phosphatase domain, the putative FtsZ-binding domain and a larger fragment encompassing both these domains. All three fragments are monomeric and the PP2C domain-containing fragments have phosphatase activity