Major intrinsic proteins (MIPs) are membrane proteins that channel water and/or uncharged solutes across membranes in all kingdoms of life. Considering the enormous number of different bacteria on earth, functional information on bacterial MIPs is scarce. Here, six MIPs (glpF1–glpF6) were identified in the genome of the Gram-positive lactic acid bacterium Lactobacillus plantarum. Heterologous expression in Xenopus laevis oocytes revealed that GlpF2, GlpF3, and GlpF4 each facilitated the transmembrane diffusion of water, dihydroxyacetone, and glycerol. As several lactic acid bacteria have GlpFs in their lactate racemization operon (GlpF1/F4 phylogenetic group), their ability to transport this organic acid was tested. Both GlpF1 and GlpF4 facilitated the diffusion of D/L-lactic acid. Deletion of glpF1 and/or glpF4 in Lb. plantarum showed that both genes were involved in the racemization of lactic acid and, in addition, the double glpF1 glpF4 mutant showed a growth delay under conditions of mild lactic acid stress. This provides further evidence that GlpFs contribute to lactic acid metabolism in this species. This lactic acid transport capacity was shown to be conserved in the GlpF1/F4 group of Lactobacillales. In conclusion, we have functionally analyzed the largest set of bacterial MIPs and demonstrated that the lactic acid membrane permeability of bacteria can be regulated by aquaglyceroporins.
Affiliations
UCLouvainSST/ISV - Institut des sciences de la vie
Bienert, G. P., Desguin, B., Chaumont, F., & Hols, P. (2013). Channel-mediated lactic acid transport: a novel function for aquaglyceroporins in bacteria. Biochemical Journal, 454(3), 559-570. https://doi.org/10.1042/BJ20130388 (Original work published 2013)