Permease involved in lysine uptake (PubMed:1315732, PubMed:24056175). In addition, functions as a lysine sensor that mediates the lysine-dependent regulation of the transcriptional activator CadC (PubMed:18086202, PubMed:24056175). In the absence of lysine, or at low lysine concentrations, LysP inhibits CadC by an interaction with the transmembrane domain of CadC. In the presence of lysine, LysP loses its ability to interact with and inhibit CadC, and acts as a lysine permease (PubMed:18086202, PubMed:24056175). H(+)(out) + L-lysine(out) = H(+)(in) + L-lysine(in) Interacts strongly with the transcriptional activator CadC in the absence of lysine or at low lysine concentrations (PubMed:18086202, PubMed:24056175). Interaction is markedly attenuated under increasing lysine levels (PubMed:24056175). Concomitant pH-dependent protonation of periplasmic amino acids in both proteins dissolves their electrostatic connections resulting in further destabilization of the CadC/LysP interaction (PubMed:24056175). Low pH promotes oligomerization of LysP (PubMed:24056175). Expression is repressed by high external lysine concentrations (PubMed:8808945, PubMed:21441513). The HTH-type transcriptional regulator ArgP is the main regulator of lysP transcription (PubMed:21441513). Under lysine-limiting growth conditions, ArgP functions as a transcriptional activator by binding directly to the lysP promoter region (PubMed:21441513). In the presence of lysine, Lys-loaded ArgP may prevent expression of the gene (PubMed:21441513). In addition, expression is activated by the global regulator Lrp under lysine-limiting conditions (PubMed:21441513). Expression is not affected by pH (PubMed:8808945). Belongs to the amino acid-polyamine-organocation (APC) superfamily. Amino acid transporter (AAT) (TC 2.A.3.1) family.