A pair of isoleucyl ‐tRNA synthetases in Bacilli fulfills complementary roles to keep fast translation and provide antibiotic resistance

AbstractIsoleucyl-tRNA synthetase (IleRS) is an essential enzyme that covalently couples isoleucine to the corresponding tRNA. Bacterial IleRSs group in two clades,ileS1 andileS2, the latter bringing resistance to the natural antibiotic mupirocin. Generally, bacteria rely on eitherileS1 orileS2 as a standalone housekeeping gene. However, we have found an exception by noticing thatBacillus species with genomicileS2 consistently also keepileS1, which appears mandatory in the familyBacillaceae. TakingPriestia (Bacillus)megaterium as a model organism, we showed that PmIleRS1 is constitutively expressed, while PmIleRS2 is stress-induced. Both enzymes share the same level of the aminoacylation accuracy. Yet, PmIleRS1 exhibited a two-fold faster aminoacylation turnover (kcat) than PmIleRS2 and permitted a notably faster cell-free translation. At the same time, PmIleRS2 displayed a 104-fold increase in itsKi for mupirocin, arguing that the aminoacylation turnover in IleRS2 could have been traded-off for antibiotic resistance. As expected, aP.megaterium strain deleted forileS2 was mupirocin-sensitive. Interestingly, an attempt to construct a mupirocin-resistant strain lackingileS1, a solution not found among species of the familyBacillaceae in nature, led to a viable but compromised strain. Our data suggest that PmIleRS1 is kept to promote fast translation, whereas PmIleRS2 is maintained to provide antibiotic resistance when needed. This is consistent with an emerging picture in which...
Source: Protein Science - Category: Biochemistry Authors: Tags: FULL ‐LENGTH PAPER Source Type: research