Progress on the Identification of the Folate Chemoreceptor of Paramecium

The ciliated protozoan Paramecium tetraurelia has been used as a simple system in which to study chemical perception and transduction events. Folic acid is an essential vitamin for P. tetraurelia and, since it is secreted by the bacteria upon which paramecia feed, may serve as a food cue. A variety of biochemical approaches have been employed in attempting to identify a membrane protein that might serve as a chemoreceptor for folate. Folate-Sepharose affinity chromatography has been used to identify folate-binding proteins in Triton X-100 solubilized pellicles. Ten proteins, or groups of proteins, consistently elute specifically from folate-Sepharose columns with folate, but not with glutamate or p-ABA-glutamate. Nine individual polypetides within the ten groups of proteins can be labeled with super(125)I. The folate-binding proteins have been further characterized by con A-Sepharose chromatography.