The Function of Pap in the Sinorhizobium meliloti Pap-Pit Low Affinity Phosphate Transport System

Abstract

<p>Pap-Pit is a low affinity phosphate transporter found in <em>S. meliloti</em> and many other microorganisms. Pit is the transporter and Pap is the Pit accessory protein. Pap has been shown to be required for the function of Pap-Pit system in <em>S. meliloti</em>. In this study, <em>pap-pit</em> or <em>pit</em> alone from three species of bacteria have been expressed <em>in trans</em> in the <em>E. coli</em> Pi uptake mutants to check their ability to complement the Pi uptake deficiency of the hosts. A visualization tag, SNAP-tag, has been fused to <em>S. meliloti</em> Pap to help determine the subcellular localization of Pap. Here we show that there is an optimal level of Pap-Pit in the cells, and Pap appears to modulate this level to optimize the function of the system. We also demonstrate that Pap is probably localized intracellularly along the cell membrane. In addition, a <em>S. meliloti pap-pit </em>deletion strain has been prepared and to be used as the background strain for site-directed mutagenesis in Pap. The highly conserved surface amino acids in Pap have been identified to be the candidates for the site-directed mutagenesis.</p>