Identification of a Spermidine Excretion Protein Complex (MdtJI) in Escherichia coli

Abstract

A spermidine excretion protein in Escherichia coli was looked for among 33 putative drug exporters thus far identified. Cell toxicity and inhibition of growth due to overaccumulation of spermidine were examined in an E. coli strain deficient in spermidine acetyltransferase, an enzyme that metabolizes spermidine. Toxicity and inhibition of cell growth by spermidine were recovered in cells transformed with pUCmdtJI or pMWmdtJI, encoding MdtJ and MdtI, which belong to the small multidrug resistance family of drug exporters. Both mdtJ and mdtI are necessary for recovery from the toxicity of overaccumulated spermidine. It was also found that the level of mdtJI mRNA was increased by spermidine. The spermidine content in cells cultured in the presence of 2 mM spermidine was decreased, and excretion of spermidine from cells was enhanced by MdtJI, indicating that the MdtJI complex can catalyze excretion of spermidine from cells. Polyamines (putrescine, spermidine, and spermine) are essential for normal cell growth (3,11,12), and their content in cells is regulated by biosynthesis, degradation, uptake, and excretion (5, 9, 10, 26). With regard to transport, the properties of three polyamine transport systems were characterized in Escherichia coli (15,16,40). They include spermidine-preferential and putrescine-specific uptake systems, which belong to the family of ATP binding cassette transporters, and a protein, PotE, involved in the excretion of putrescine by a putrescineornithine antiporter activity. Furthermore, it has been reported that cadaverine and aminopropylcadaverine function as compensatory polyamines for cell growth (13), and CadB, a cadaverine-lysine antiporter, is strongly involved in cell growth at acidic pH, like PotE (23,33,34,41). Analogous to the speF-potE operon (18), cadB is one component of the cadBA operon, in which cadA encodes lysine decarboxylase (22,41) and is induced by acidic pH and lysine (23). The cadBA and speF-potE operons contribute to an increase in the pH of the extracellular medium through excretion of cadaverine and putrescine, the consumption of a proton, and a supply of carbon dioxide during the decarboxylation reaction (33, 38), so the expression of these two operons is important for cell growth at acidic pH.Although PotE and CadB excrete putrescine and cadaverine at acidic pH, they function as uptake proteins for putrescine and cadaverine at neutral pH (16,33). Thus, no polyamine excretion proteins that function at neutral pH have been identified to date. Overaccumulated spermidine is either metabolized by acetylation of spermidine, in a reaction catalyzed by spermidine acetyltransferase (6), or neutralized by the increase in L-glycerol 3-phosphate (27). In this study, we looked for spermidine excretion proteins among putative drug exporters comprising five families (the major facilitator family, the small multidrug resistance [SMR] family, the resistance-nodulationcell division family, the ATP binding cassette family, and the multidrug and toxic compound extrusion family) (25) a...

Surface-Localized Spermidine Protects the Pseudomonas aeruginosa Outer Membrane from Antibiotic Treatment and Oxidative Stress

“…There is evidence of putrescine and cadaverine secretion in E. coli using antiporter transport proteins (28,45). A spermidine excretion protein complex, MdtJI, which belongs to the small multidrug resistance family of drug exporters, has been identified in E. coli by Higashi et al (24). The function of secreted polyamines is unclear, but it is tempting to speculate secreted polyamines may play a role in cross-linking the anionic biofilm matrix polymers or may provide an attractive conditioning layer.…”

Effects of polyamines on protein synthesis and growth of Escherichia coli

“…Although it is normally difficult for spermidine to over-accumulate in E. coli due to the existence of spermidine acetyltransferase (45) as well as spermidine excretion protein complex (MdtJI) (46), the mechanism of detoxification of excessive spermidine levels was studied (47). E. coli CAG2242 cells are deficient in the speG gene encoding spermidine acetyltransferase (48).…”

A Novel Putrescine Exporter SapBCDF of Escherichia coli

“…In previous studies, MdtJI of E. coli (25) and Blt of Bacillus subtilis (26) were reported as spermidine exporters. Additionally, in Shigella flexneri it was reported that MdtJI was a putrescine exporter (27).…”

“…However, in these three reports the strains overexpressing genes of polyamine exporters were used for assays of polyamine export. Furthermore, none of these previous studies analyzed the decreased polyamine export activity of the mutant strains with the deletion of genes encoding polyamine exporters nor measured the polyamine concentration of the culture supernatant (25)(26)(27). It was previously reported that PotE is a putrescine-ornithine antiporter at acidic pH (19).…”