Abstract
The uncharacterized protein family 0016 (UPF0016) is a family of secondary ion transporters implicated in calcium homeostasis and some diseases. More precisely, genetic variants of the human UPF0016 ortholog transmembrane protein 165 (TMEM165) have been linked to congenital disorders of glycosylation (CDG). The Saccharomyces cerevisiae ortholog Gdt1p has been shown to be involved in calcium homeostasis and protein glycosylation. Moreover, plant and bacterial UPF0016 members appear to have putative roles in Mn(2+) homeostasis. Here, we produced the yeast UPF0016 member Gdt1p in the bacterial host Lactococcus lactis Using Mn(2+)-induced quenching of Fura-2-emitted fluorescence, we observed that Gdt1p mediates Mn(2+) influx, in addition to its previously reported regulation of Ca(2+) influx. The estimated K(m) values of Gdt1p of 15.6 ± 2.6 μm for Ca(2+) and 83.2 ± 9.8 μm for Mn(2+) indicated that Gdt1p has a higher affinity for Ca(2+) than for Mn(2+) In yeast cells, we found that Gdt1p is involved in the resistance to high Mn(2+) concentration and controls total Mn(2+) stores. Lastly, we demonstrated that GDT1 deletion affects the activity of the yeast Mn(2+)-dependent Sod2p superoxide dismutase, most likely by modulating cytosolic Mn(2+) concentrations. Taken together, we obtained first evidence that Gdt1p from yeast directly transports manganese, which strongly reinforces the suggested link between the UPF0016 family and Mn(2+) homeostasis and provides new insights into the molecular causes of human TMEM165-associated CDGs. Our results also shed light on how yeast cells may regulate Golgi intraluminal concentrations of manganese, a key cofactor of many enzymes involved in protein glycosylation.