title: Porins increase copper susceptibility of Mycobacterium tuberculosis.
abstract: Copper resistance mechanisms are crucial for many pathogenic bacteria, including Mycobacterium tuberculosis, during infection because the innate immune system utilizes copper ions to kill bacterial intruders. Despite several studies detailing responses of mycobacteria to copper, the pathways by which copper ions cross the mycobacterial cell envelope are unknown. Deletion of porin genes in Mycobacterium smegmatis leads to a severe growth defect on trace copper medium but simultaneously increases tolerance for copper at elevated concentrations, indicating that porins mediate copper uptake across the outer membrane. Heterologous expression of the mycobacterial porin gene mspA reduced growth of M. tuberculosis in the presence of 2.5 μM copper by 40% and completely suppressed growth at 15 μM copper, while wild-type M. tuberculosis reached its normal cell density at that copper concentration. Moreover, the polyamine spermine, a known inhibitor of porin activity in Gram-negative bacteria, enhanced tolerance of M. tuberculosis for copper, suggesting that copper ions utilize endogenous outer membrane channel proteins of M. tuberculosis to gain access to interior cellular compartments. In summary, these findings highlight the outer membrane as the first barrier against copper ions and the role of porins in mediating copper uptake in M. smegmatis and M. tuberculosis.
authors.affiliation: Department of Microbiology.
authors.forename: Alexander
authors.initials: A
authors.lastname: Speer
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Rowland
authors.forename: Mehri
authors.initials: M
authors.lastname: Haeili
authors.forename: Michael
authors.initials: M
authors.lastname: Niederweis
authors.forename: Frank
authors.initials: F
authors.lastname: Wolschendorf
mesh_terms: D003300:Copper / Q000633:toxicity*; D015870:Gene Expression; D008826:Microbial Sensitivity Tests; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D018272:Porins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D018272:Porins; D011994:Recombinant Proteins; C121838:mspA protein, Mycobacterium smegmatis; D003300:Copper