Short repeats in the spa gene of Staphylococcus aureus are prone to nonsense mutations: stop codons can be found in strains isolated from patients with generalized infection

Protein A of Staphylococcus aureus strain NCTC8325 interacted with heparin

Heparin, known for its anticoagulant activity, is commonly used as the coatings of medical devices. The attaching of Staphylococcus aureus, a prominent human and animal pathogen, to the heparin coatings usually leads to catheter-related bloodstream infections. Hence, the study of the interaction between heparin and S. aureus surface proteins is desired. Here, we found that protein A (SpA) of S. aureus was a heparin-binding protein, contributing to the interaction between S. aureus and heparin. The cell-wall-anchored SpA was one of the most critical S. aureus virulence factors with a lysin-like motif (LysM). When SpA was mutated to remove the LysM motif, the heparin-binding capability of SpA dropped 50%. The in-frame deletion of spa also reduced the heparin-binding capability of S. aureus. There was 1.3-fold more of heparin bound to wild type S. aureus than the Δspa::Em strain. These results would help understand the host-microbe interaction and the infection by S. aureus.

The history of mutational pressure changes during the evolution of adeno-associated viruses: A message to gene therapy and DNA-vaccine vectors designers

The use of virus-associated vectors for gene therapy and vaccination have emerged as safe and effective delivery system. Like all other genetic materials, these vehicles are also prone to spontaneous mutations. To understand what types of nucleotide mutations are expected in the vector, one needs to know distinct characteristics of mutational process in the corresponding virus. In this study we analyzed mutational pressure directions along the length of the genomes of all types of primate adeno-associated viruses (AAV) that are frequently used in gene therapy or DNA-vaccines. We observed clear evidences of transcription-associated mutational pressure in AAV: nucleotide usage biases are changing drastically after each of the three promoters: the higher the rate of transcription, the stronger the bias towards GC to AT mutations. Moreover, the usage of G decreased at the lower transcription rate (after P19 promoter) than the usage of C (after P40 promoter). Since nucleotide usage biases are retrospective indices, we created a scenario of changes in transcriptional map during the AAV evolution. Current mutational pressure directions are different for AAV types, while all of them demonstrate high rates of T to C transitions in the second long ORF. Since transcription rate and cell tropism are the main factors determining the preferable direction of nucleotide mutations in AAV, mutational pressure should be checked experimentally in DNA vectors before their final design with the aim to make the transferred gene more stable against those mutations.