However, while all mutants containing this residue had a positive

However, while all mutants containing this residue had a positive effect on invasion into CT-26 cells, the exact contribution of this residue could not be assessed as additional mutations were present in all clones. Further analysis of individual clones from each bank or the application of additional selection is required due to the diversity uncovered (25 of the 32 clones analyzed AZD2014 chemical structure were different). This diversity and the enhanced invasion of all the clones examined confirms that amino acids additional to the ones previously examined [17] can modulate the affinity for CDH1. Despite the analysis of 32 clones from our enriched bank of InlA variants, we failed

to detect mutations that yielded invasion rates comparable to the murinized InlA described by Y-27632 nmr Wollert and coworkers [17]. In terms of developing usable models of murine listeriosis the approach of ‘murinizing’ the bacterial strain arguably has a number of benefits over the development of humanized mouse lines. Development of the modified bacterium will permit utilization of this strain in existing mouse lines (including existing knock-out murine models) and distribution of the murinized strain is relatively straightforward, as is the creation of new mutations in the EGD-e InlA m * background. However, the 2-fold enhanced adherence and invasion to human (Caco-2) cells of the L. monocytogenes Lmo-InlAm

[17] could be a potential cause for concern as it is

suggestive of a slight enhancement of virulence towards humans. The procedure used to create that strain required multiple prolonged incubations at 42°C [17, 33]. It has been recently shown that high temperature growth of L. monocytogenes can induce spontaneous mutation, suggesting that high temperature growth should be minimized to avoid the acquisition of secondary mutations [34]. We re-created the InlA mutations described by Wollert et al., [17] to create EGD-e InlA m * using only two temperature shifts to 37°C and six passages under non-selective conditions [20]. Another difference between the Lmo-InlAm and EGD-e InlA m * strain were the nucleotide changes made to create the BCKDHA mutated amino acids. In the EGD-e InlA m * strain the two codons were chosen based on the codon usage from genome analysis, with the most commonly used triplets applied. In each case usage was 50% higher than the one used in Lmo-InlAm. For the asparagine 192, AAT compared to the AAC codon was chosen (31.8 vs 14.4 per 1000 codons). While for serine 369 TCT compared to TCG codon was chosen (12.8 vs 6.2 per 1000 codons). The invasion data for Lmo-InlAm agreed with the biophysical characterization which showed an enhanced interaction for InlA with CDH1 [35] however as recently shown, synonymous mutations leading to mRNA sequence changes can also affect substrate specificity or protein activity [36].

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