Receptor for the attractant L-serine and related amino acids. Is also responsible for chemotaxis away from a wide range of repellents, including leucine, indole, and weak acids. Chemotactic-signal transducers respond to changes in the concentration of attractants and repellents in the environment, transduce a signal from the outside to the inside of the cell, and facilitate sensory adaptation through the variation of the level of methylation. Attractants increase the level of methylation while repellents decrease the level of methylation, the methyl groups are added by the methyltransferase CheR and removed by the methylesterase CheB. Found predominantly at cell poles. Belongs to the methyl-accepting chemotaxis (MCP) protein family.