Nic1p, a relative of bacterial transition metal permeases in Schizosaccharomyces pombe, provides nickel ion for urease biosynthesis

Abstract

The Schizosaccharomyces pombe genome sequencing project identified an open reading frame (O74869 and O74912, named Nic1p in the present study) with significant similarity to members of a family of bacterial transition metal permeases. These uptake systems transport Ni2+ ion with extremely high affinity across the bacterial cytoplasmic membrane, but they differ in selectivity toward divalent transition metal cations. An S. pombe mutant harboring an interrupted nic1 allele (nic1-1) was strongly impaired in 63Ni2+ uptake in the presence of a high molar ratio of Mg2+ relative to Ni2+, conditions that reflect the natural situation. Under these conditions, the nic1-1 mutant contained only background activities of the nickel-dependent cytoplasmic enzyme urease and could not catabolize urea. Among a series of divalent transition metal cations tested (Cd2+, Co2+, Cu2+, Mn2+, and Zn2+), only Co2+ caused considerable inhibition of Nic1p-mediated Ni2+ uptake. On the other hand, experiments with 57Co2+ (at nM concentrations) did not show significant differences in Co2+ uptake between the nic1-1 mutant and the parental strain. Our data suggest that Nic1p acts as a plasma-membrane nickel transporter in fission yeast, a finding that invites searches for isologous counterparts in higher eukaryotes.