Mediates chemotaxis towards five attractant amino acids (leucine, isoleucine, valine, methionine and cysteine). Probably transduces the signal from the substrate-binding protein BasB to the histidine kinase CheA. Interacts with CheA, CheY, CheW1 and CheW2. Methylated by CheR. Mutants completely lose the chemotactic response towards leucine, isoleucine, valine, methionine and cysteine, but they still respond to arginine. Belongs to the methyl-accepting chemotaxis (MCP) protein family.