Discovery and characterization of a second BlaRI-type two-component
signaling system in Mycobacterium abscessus
Abstract
Pathogens utilize a diverse set of signal transduction mechanisms to
respond to host-derived stresses, with phosphotransfer-mediated two
component systems (TCS) playing key roles in virulence factor
regulation. Staphylococcus aureus encodes an alternative
protease-mediated TCS prototype known as BlaRI involved in inducible
β-lactam resistance. BlaR senses extracellular β-lactams, leading to
activation of a cytoplasmic protease domain able to cleave DNA-bound
BlaI dimers, de-repressing blaRI and blaZ (β-lactamase).
The two known mycobacterial BlaRI-type systems in M. tuberculosis
(Mtb) and M. abscessus ( Mab) are characterized by BlaR
orthologs with conserved zinc metalloprotease domain but lacking an
extracellular β-lactam binding domain. BlaIR Mtb
and BlaIR Mab (renamed BlaIR to reflect inverted
genomic organization) regulate β-lactamase expression ( Mtb only)
and respiration (both Mtb and Mab). In this study, we have
identified a second BlaRI-type system in Mab, MAB_4287-4288
(BlaIR2). Using RT-PCR and EMSA, we established that BlaIR2
Mab is encoded within a five gene operon, a
unique characteristic in BlaRI-type systems, and is auto-regulatory.
Identification of putative BlaI2 Mab binding
motifs revealed a predicted regulon comprised of several genes involved
in respiration, with some overlap with the BlaI1
Mab regulon. Finally, our data demonstrated that
BlaIR2 Mab was also induced by the respiration
inhibitor clofazimine (CFZ) similarly to BlaIR1
Mab, with evidence of possible crosstalk between
BlaRI systems. Overall, this study established MAB_4287-4288 (BlaIR2
Mab) as a second BlaRI-type system in Mab,
whose role may overlap or intersect that of BlaRI1
Mab. However, the activation mechanism and full
role of BlaIR2 Mab in Mab stress responses
and pathogenesis remains to be elucidated.