In vitro expression and functional characterization of NPA motifs in aquaporins of Nosema bombycis

Abstract

Nosema bombycis contains functional aquaporins (NbAQPs), which are key targets for exploring the mechanism of N. bombycis infection; however, the regulation of these NbAQPs remains unknown. The two highly conserved asparagine-proline-alanine sequences (NPA motifs) play important roles in AQP biogenesis. As part of this study, we constructed a series of NbAQP mutants (NbAQP_NPA1, NbAQP_NPA2, and NbAQP_NPA1,2) and expressed them in BmN cells. The results showed that mutations in either NPA motif or in both NPA motifs did not affect NbAQP expression in vitro. After expression in Xenopus laevis oocytes, those injected with wild-type NbAQP rapidly expanded, whereas oocytes injected with NbAQP_NPAs did not significantly change in size. The associated water permeability (pf) of NbAQP_NPAs was significantly reduced five-six times compared to that of wild-type NbAQP. These results indicated that NPA motifs are necessary for the water channel function of AQPs in N. bombycis. The present study shows for the first time that the NbAQP NPA motif has an impact on the water permeability of aquaporin in N. bombycis, thereby providing a platform for further research into the mechanisms underlying the regulation of NbAQP expression.

Germination of Microsporidian Spores: The Known and Unknown

“…Moreover, the polyamine transporters or permeases encoded by some microsporidia may contribute to germination by absorbing sugars, cations, and nicotinic acids [98,99]. Altogether, increasing osmotic pressure induces spores to absorb water through functional aquaporins, resulting in swelling of the polaroplast and posterior vacuole [48,51,100]. The spore wall withstands osmotic pressure for some time but eventually ruptures at the apex, where it is thin, eventually leading to polar filament discharge [30].…”

Plant Aquaporins in Infection by and Immunity Against Pathogens – A Critical Review

“…The outward end of HB and inward end of LE contain a pair of asparagine (N), proline (P), and alamine (A) tandem (NPA) motifs, which constitute the central channel through the membrane (Kirscht et al, 2016). Two NPAs form a conical funnel or traditional hourglass, which are linked at the tip and open outward from LE and inward from TM5 (Törnroth-Horsefield et al, 2010), and are essential for AQP function (Wree et al, 2011; Chen et al, 2018). Within LE, TM2 and TM5, the aromatic/arginine (Ar/R) selective filter (SF) is formed by four residues including aromatic amino acids and an arginine (R) residue; hence its name (de Groot et al, 2003).…”