Evolution, function and roles in drug sensitivity of trypanosome aquaglyceroporins.

Mark C Field,Juan F Quintana

doi:10.1017/s0031182021000354

Abstract

Aquaglyceroporins (AQPs) are membrane proteins that function in osmoregulation and the uptake of low molecular weight solutes, in particular glycerol and urea. The AQP family is highly conserved, with two major subfamilies having arisen very early in prokaryote evolution and retained by eukaryotes. A complex evolutionary history indicates multiple lineage-specific expansions, losses and not uncommonly a complete loss. Consequently, the AQP family is highly evolvable and has been associated with significant events in life on Earth. In the African trypanosomes, a role for the AQP2 paralogue, in sensitivity to two chemotherapeutic agents, pentamidine and melarsoprol, is well established, albeit with the mechanisms for cell entry and resistance unclear until very recently. Here, we discuss AQP evolution, structure and mechanisms by which AQPs impact drug sensitivity, suggesting that AQP2 stability is highly sensitive to mutation while serving as the major uptake pathway for pentamidine.

Highlights

Aquaglyceroporins (AQPs) were first identified in the 1990s as membrane proteins with functions in osmoregulation and the translocation of low molecular weight solutes, including glycerol and urea (Preston et al, 1992)
Using genome-wide RNAi-mediated genetic screening and functional assays, the locus encoding the closely related AQP2 and AQP3 was identified as a bona fide hit for pentamidine/melarsoprol cross-resistance (Graf et al, 2015b)
Further biochemical and genetic manipulation studies demonstrated that deletion of AQP2, but not AQP3, led to a significant increase in the EC50 of both compounds, mirroring the behaviour observed in previously generated laboratory strains and field isolates (Munday et al, 2014; Graf et al, 2015b; Song et al, 2016). Other observations such as localization to the flagellar pocket in the bloodstream form (Munday et al, 2014; Graf et al, 2015b; Song et al, 2016; Quintana et al, 2020), as well as the unusual pore structure discussed above, led to the hypothesis that pentamidine and melarsoprol are likely to interact with high affinity to AQP2 located in the flagellar pocket (Alghamdi et al, 2020), posing the question of how these compounds are internalized and the mechanisms for resistance

Summary

Introduction

Aquaglyceroporins (AQPs) were first identified in the 1990s as membrane proteins with functions in osmoregulation and the translocation of low molecular weight solutes, including glycerol and urea (Preston et al, 1992). In addition to interactions between trans-membrane domains, two major selectivity filters restrict the molecular weights and properties of the solutes being translocated by AQPs and that can effectively pass through the central pore; these are the ar/R and NPA/NPA motifs (Fig. 1) (Beitz, 2005; Baker et al, 2013; Verkman et al, 2014; Munday et al, 2015; Fairlamb and Horn, 2018).

Results

Conclusion