Enzyme activity and thermostability of a non-specific nuclease from Yersinia enterocolitica subsp. palearctica by site-directed mutagenesis

Background: To identify the critical amino acid residues that contribute to the high enzyme activity and good thermostability of Yersinia enterocolitica subsp. palearctica (Y. NSN), 15 mutants of Y. NSN were obtained by site-directed mutagenesis in this study. And their enzyme activity and thermostability were assayed. Effect of several factors on the enzyme activity and thermostability of Y. NSN, was also investigated. Results: The results showed that the I203F and D264E mutants retained approximately 75% and 70% enzyme activity, respectively, compared to the wild-type enzyme. In addition to the I203F and D264E mutants, the mutant E202A had an obvious influence on the thermostability of Y. NSN. According to the analysis of enzyme activity and thermostability of Y. NSN, we found that Glu202, Ile203 and Asp264 might be the key residues for its high enzyme activity and good thermostability. Conclusions: Among all factors affecting enzyme activity and thermostability of Y. NSN, they failed to explain the experimental results well. One reason might be that the enzyme activity and thermostability of Y. NSN were affected not only by a single factor but also by the entire environment.

Lys-413 of S-phase mRNA cycling sequence binding protein from Leishmania donovani (LdCSBP) is modified through monoubiquitination that is responsible for inhibition of its riboendonuclease activity.

In addition to well-known process of proteasome-mediated degradation of polyubiquitinated proteins, monoubiquitination of proteins is also an important post-translational modification that regulates various non-degradative cellular processes like protein trafficking, cellular signalling, DNA replication and DNA repair. We have previously characterized a multi-domain cycling sequence binding protein LdCSBP from Leishmania donovani, which binds specifically to a conserved CAUAGAAG octamer containing RNAs via its uniquely arranged CCCH type Zn-fingers and degrades them using its Smr endonuclease domain, indicative of its potential role in the turnover of the S-phase mRNAs. Remarkably, its riboendonuclease activity is inhibited due to the incorporation of a monoubiquitin residue in the ZnF domain, though the target Lys residue remains unknown. Here, we report through systematic mutation of Lys residue to Ala that Lys-413 in LdCSBP is the site of monoubiquitination. However, the amino acid motif around the target Lys in LdCSBP is not consensus with any previously known monoubiquitination site, though partial homology is observed with a subset of recently identified mammalian ubiquitination target sites. Interestingly, Lys-413 of LdCSBP is conserved in the homologous annotated proteins from the related kinetoplastida parasites, suggesting similar monoubiquitination-mediated regulation of RNA endonuclease activity in the organisms.

PCR-based detection of genes encoding virulence determinants in Staphylococcus aureus from bovine subclinical mastitis cases

The present study was carried out to genotypically characterize Staphylococcus aureus (S. aureus) isolated from bovine mastitis cases. A total of 37 strains of S. aureus were isolated during processing of 552 milk samples from 140 cows. The S. aureus strains were characterized phenotypically, and were further characterized genotypically by polymerase chain reaction using oligonucleotide primers that amplified genes encoding coagulase (coa), clumping factor (clfA), thermonuclease (nuc), enterotoxin A (entA), and the gene segments encoding the immunoglobulin G binding region and the X region of protein A gene spa. All of the isolates yielded an amplicon with a size of approximately 1,042 bp of the clfA gene. The amplification of the polymorphic spa gene segment encoding the immunoglobulin G binding region was observed in 34 isolates and X-region binding was detected in 26 isolates. Amplification of the coa gene yielded three different products in 20, 10, and 7 isolates. The amplification of the thermonuclease gene, nuc, was observed in 36 out of 37 isolates. All of the samples were negative for the entA gene. The phenotypic and genotypic findings of the present strategies might provide an understanding of the distribution of the prevalent S. aureus clones among bovine mastitis isolates, and might aid in the development of steps to control S. aureus infections in dairy herds.