Rand protease is a serine protease that shared common characteristics with members of the MEROPS S8 subtilisin family. It is thermostable, highly stable in organic solvent and broad in specificity. Many structures of homologous protein solved by X-ray crystallography and NMR have been deposited to Protein Data Bank (PDB) which allowed this study to rely on structure prediction by deep learning to build three-dimensional (3D) structure of full length and mature Rand protease (flRP and mRP). In silico cysteine mutation to 7 predicted high affinity Ca2+ coordinating residues were introduced, and the mutants were subjected to molecular dynamics simulation to study its effect on flRP and mRP. MD simulation showed a marked increase in flexibility of the pro-peptide segment indicating the impact of single cysteine substitution at high affinity Ca2+ coordinating residues to autolysis of flRP. MD simulation for mRP reaffirmed the role of Ca2+ coordinating sites in providing stability to Rand protease. In addition, these residues also affect the autolysis, folding and hydrophobicity of RP. Essential dynamics observed large contribution of the first few eigenvectors of flRP, mRP and their high affinity Ca2+ coordinating residues mutants to the TMSF values which indicates that these values account for a large portion of the overall atomic fluctuations. These results have given a more comprehensive understanding on the role of cysteine substituted Ca2+ coordinating surface loop to the structure of flRP and mRP which are important in contributing to the structural stability of subtilisin.Communicated by Ramaswamy H. Sarma.
Polymer blends have attracted significant research interest due to their potential use as power cable insulating materials. Specifically, polypropylene (PP) blends offer improved dielectric properties over conventional crosslinked polyethylene insulating materials attributable to PP's high melting temperatures, hence high rated voltages. Despite numerous promising findings have been reported regarding the potential application of PP blends as power cable insulating materials, there have been relatively less investigations into the dielectric effects of incorporating nanofillers into PP blends. The current work therefore explores the influence of calcined magnesia (MgO) nanofiller on the structure and dielectric properties of PP blended with ethylene-octene copolymer (EOC). Nanofiller-wise, calcination of MgO does not significantly affect the structure of MgO, albeit that water-related molecules are removed from MgO. Upon adding the calcined MgO to the PP/EOC blend, the breakdown performance of the PP/EOC/MgO blend nanocomposites becomes jeopardized, especially under the direct current field. This is primarily attributed to the presence of residue water molecules within the PP/EOC/MgO blend nanocomposites, even after MgO calcination. Although the addition of the calcined MgO to the PP blend does not result in favorable dielectric properties, the findings suggest that nanostructuration of PP blends could be further explored to pave the way for the development of nanostructured PP blends for use in advanced power cable insulation applications.