TY - JOUR
T1 - Human trypanolytic factor APOL1 forms pH-gated cation-selective channels in planar lipid bilayers
T2 - Relevance to trypanosome lysis
AU - Thomson, Russell
AU - Finkelstein, Alan
PY - 2015/3/3
Y1 - 2015/3/3
N2 - Apolipoprotein L-1 (APOL1), the trypanolytic factor of human serum, can lyse several African trypanosome species including Trypanosoma brucei brucei, but not the human-infective pathogens T. brucei rhodesiense and T. brucei gambiense, which are resistant to lysis by human serum. Lysis follows the uptake of APOL1 into acidic endosomes and is apparently caused by colloid-osmotic swelling due to an increased ion permeability of the plasma membrane. Here we demonstrate that nanogram quantities of full-length recombinant APOL1 induce ideally cation-selective macroscopic conductances in planar lipid bilayers. The conductances were highly sensitive to pH: their induction required acidic pH (pH 5.3), but their magnitude could be increased 3,000-fold upon alkalinization of the milieu (pKa = 7.1). We show that this phenomenon can be attributed to the association of APOL1 with the bilayer at acidic pH, followed by the opening of APOL1-induced cationselective channels upon pH neutralization. Furthermore, the conductance increase at neutral pH (but not membrane association at acidic pH) was prevented by the interaction of APOL1 with the serum resistance-associated protein, which is produced by T. brucei rhodesiense and prevents trypanosome lysis by APOL1. These data are consistent with a model of lysis that involves endocytic recycling of APOL1 and the formation of cation-selective channels, at neutral pH, in the parasite plasma membrane.
AB - Apolipoprotein L-1 (APOL1), the trypanolytic factor of human serum, can lyse several African trypanosome species including Trypanosoma brucei brucei, but not the human-infective pathogens T. brucei rhodesiense and T. brucei gambiense, which are resistant to lysis by human serum. Lysis follows the uptake of APOL1 into acidic endosomes and is apparently caused by colloid-osmotic swelling due to an increased ion permeability of the plasma membrane. Here we demonstrate that nanogram quantities of full-length recombinant APOL1 induce ideally cation-selective macroscopic conductances in planar lipid bilayers. The conductances were highly sensitive to pH: their induction required acidic pH (pH 5.3), but their magnitude could be increased 3,000-fold upon alkalinization of the milieu (pKa = 7.1). We show that this phenomenon can be attributed to the association of APOL1 with the bilayer at acidic pH, followed by the opening of APOL1-induced cationselective channels upon pH neutralization. Furthermore, the conductance increase at neutral pH (but not membrane association at acidic pH) was prevented by the interaction of APOL1 with the serum resistance-associated protein, which is produced by T. brucei rhodesiense and prevents trypanosome lysis by APOL1. These data are consistent with a model of lysis that involves endocytic recycling of APOL1 and the formation of cation-selective channels, at neutral pH, in the parasite plasma membrane.
KW - APOL1
KW - African trypanosome
KW - Apolipoprotein L-I
KW - PH-gated channel
KW - SRA
UR - http://www.scopus.com/inward/record.url?scp=84924370994&partnerID=8YFLogxK
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U2 - 10.1073/pnas.1421953112
DO - 10.1073/pnas.1421953112
M3 - Article
C2 - 25730870
AN - SCOPUS:84924370994
SN - 0027-8424
VL - 112
SP - 2894
EP - 2899
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 9
ER -