Surface Mutation Thr34His Facilitates Purification of Haemophilus influenza Carbonic Anhydrase via Metal Affinity Chromatography

In order to pursue Haemophilus influenza carbonic anhydrase (HICA) as a potential drug target, easy and efficient purification methods must be developed. While immobilized metal affinity chromatography (IMAC) may be used, complications with polyhistidine tags is a concern. Inspired by the endogenous metal affinity of Escherichia coli β-carbonic anhydrase (ECCA), we suggest that the generation of histidine clusters on HICA’s surface will facilitate its purification by metal affinity chromatography without the potential interference of His-tags. Here we investigate the Thr34His mutation as a method to generate metal affinity in HICA. Since Thr34His is located only 5.3 Å away from His32, the two residues make a vicinal histidine pair that can interact with nickel resin. We report successful generation of Thr34His HICA mutant plasmid via site-directed mutagenesis. To obtain mutant protein for metal affinity chromatography, Thr34His HICA was overexpressed in E. coli cells and isolated as a cell lysate with a concentration of 20.2 ± 0.6 mg/mL. Metal affinity chromatography was performed on the sample, and the chromatography fractions were analyzed by SDS-PAGE in order to assess the metal affinity of the mutant. SDS-PAGE revealed that while Thr34His HICA eluted at low 10 mM and 25 mM concentrations of imidazole, 150 mM imidazole was required to fully elute the mutant. These results suggest that through the generation of surface histidine pairs, HICA can be engineered to have metal affinity and thus be easily purified via IMAC

Ile126His and Lys129His Surface Mutations Aid in Purification of Haemophilus influenzae Carbonic Anhydrase Through Increased Metal Ion Affinity

Carbonic anhydrase (CA) is an enzyme that plays a major role in the survival of many bacterial, chiefly Haemophilus influenzae. Because of its crucial role in bacteria, recent research has turned to CA as a possible target for drug development to kill bacteria and possibly cure different bacterial diseases. While research has focused on this drug target, the isolation and purification of specific types of CA has remained a major obstacle for further research. The current method of immobilized metal affinity chromatography (IMAC) with a Ni-NTA column is used widely for CA purification; however, the H. influenzae carbonic anhydrase (HICA) has very low binding affinity to Ni-NTA column and cannot be effectively purified. Previous research has shown that the addition of a surface histidine residue at D125 increases HICA protein binding affinity to the nickel column. In our research, we suggest that the further insertion of surface histidine residues will increase the HICA protein binding affinity to a Ni-NTA column. The addition of the Ile126His and Lys129His mutations to the Asp125His HICA mutant through site directed mutagenesis is presented here to observe the binding affinity of the mutant HICA to a nickel column, The newly synthesized HICA mutant is reported here to enhance the binding affinity of HICA to the Ni-NTA column, eluting from the column upon addition of between 50 and 100 mM imidazole, as opposed to wild-type HICA protein that elutes upon the addition of 25 mM imidazole. To confirm the presence of the mutant HICA protein in the 50 and 100 mM fractions, SDS-PAGE analysis was used and it is reported here that molecular weight of the monomer of the protein was 19.6 kDa. These promising results indicate that the addition of multiple histidine residues to the HICA enzyme can increase its binding affinity to a Ni-NTA column. As opposed to adding polyhistidine tags to the HICA protein, these results suggest a straightforward strategy to purify the HICA enzyme as well as other proteins for further research in drug development

Cluster M Mycobacteriophages Bongo, PegLeg, and Rey with Unusually Large Repertoires of tRNA Isotopes

Genomic analysis of a large set of phages infecting the common hostMycobacterium smegmatis mc2155 shows that they span considerable genetic diversity. There are more than 20 distinct types that lack nucleotide similarity with each other, and there is considerable diversity within most of the groups. Three newly isolated temperate mycobacteriophages, Bongo, PegLeg, and Rey, constitute a new group (cluster M), with the closely related phages Bongo and PegLeg forming subcluster M1 and the more distantly related Rey forming subcluster M2. The cluster M mycobacteriophages have siphoviral morphologies with unusually long tails, are homoimmune, and have larger than average genomes (80.2 to 83.7 kbp). They exhibit a variety of features not previously described in other mycobacteriophages, including noncanonical genome architectures and several unusual sets of conserved repeated sequences suggesting novel regulatory systems for both transcription and translation. In addition to containing transfer-messenger RNA and RtcB-like RNA ligase genes, their genomes encode 21 to 24 tRNA genes encompassing complete or nearly complete sets of isotypes. We predict that these tRNAs are used in late lytic growth, likely compensating for the degradation or inadequacy of host tRNAs. They may represent a complete set of tRNAs necessary for late lytic growth, especially when taken together with the apparent lack of codons in the same late genes that correspond to tRNAs that the genomes of the phages do not obviously encode

Comparative genomics of Cluster O mycobacteriophages

Mycobacteriophages - viruses of mycobacterial hosts - are genetically diverse but morphologically are all classified in the Caudovirales with double-stranded DNA and tails. We describe here a group of five closely related mycobacteriophages - Corndog, Catdawg, Dylan, Firecracker, and YungJamal - designated as Cluster O with long flexible tails but with unusual prolate capsids. Proteomic analysis of phage Corndog particles, Catdawg particles, and Corndog-infected cells confirms expression of half of the predicted gene products and indicates a non-canonical mechanism for translation of the Corndog tape measure protein. Bioinformatic analysis identifies 8-9 strongly predicted SigA promoters and all five Cluster O genomes contain more than 30 copies of a 17 bp repeat sequence with dyad symmetry located throughout the genomes. Comparison of the Cluster O phages provides insights into phage genome evolution including the processes of gene flux by horizontal genetic exchange

Comparative Genomics of Cluster O Mycobacteriophages

Mycobacteriophages – viruses of mycobacterial hosts – are genetically diverse but morphologically are all classified in the Caudovirales with double-stranded DNA and tails. We describe here a group of five closely related mycobacteriophages – Corndog, Catdawg, Dylan, Firecracker, and YungJamal – designated as Cluster O with long flexible tails but with unusual prolate capsids. Proteomic analysis of phage Corndog particles, Catdawg particles, and Corndog-infected cells confirms expression of half of the predicted gene products and indicates a non-canonical mechanism for translation of the Corndog tape measure protein. Bioinformatic analysis identifies 8–9 strongly predicted SigA promoters and all five Cluster O genomes contain more than 30 copies of a 17 bp repeat sequence with dyad symmetry located throughout the genomes. Comparison of the Cluster O phages provides insights into phage genome evolution including the processes of gene flux by horizontal genetic exchange

WSES guidelines for management of Clostridium difficile infection in surgical patients

In the last two decades there have been dramatic changes in the epidemiology of Clostridium difficile infection (CDI), with increases in incidence and severity of disease in many countries worldwide. The incidence of CDI has also increased in surgical patients. Optimization of management of C difficile, has therefore become increasingly urgent. An international multidisciplinary panel of experts prepared evidenced-based World Society of Emergency Surgery (WSES) guidelines for management of CDI in surgical patients.Peer reviewe

Whole genome comparison of a large collection of mycobacteriophages reveals a continuum of phage genetic diversity

The bacteriophage population is large, dynamic, ancient, and genetically diverse.Limited genomic information shows that phage genomes are mosaic, and the genetic architecture ofphage populations remains ill-defined. To understand the population structure of phages infectinga single host strain, we isolated, sequenced, and compared 627 phages of Mycobacteriumsmegmatis. Their genetic diversity is considerable, and there are 28 distinct genomic types (clusters)with related nucleotide sequences. However, amino acid sequence comparisons show pervasivegenomic mosaicism, and quantification of inter-cluster and intra-cluster relatedness revealsa continuum of genetic diversity, albeit with uneven representation of different phages. Furthermore,rarefaction analysis shows that the mycobacteriophage population is not closed, and there isa constant influx of genes from other sources. Phage isolation and analysis was performed by a largeconsortium of academic institutions, illustrating the substantial benefits of a disseminated, structuredprogram involving large numbers of freshman undergraduates in scientific discovery