Finding parts for bacterial motors.

Finding parts for bacterial motors

Depending on what chemical is in the vicinity, a bacterium moves toward or away from it by twirling tiny hairlike projections called flagella that are attached to a molecular "motor" at one end of the organism. When the motor turns counterclockwise, the flagella form into a propeller and the organism swims smoothly forward. In clockwise rotation, the flagella come apart and the bacterium tumbles head over heel, reorienting its swimming direction (SN:5/12/84, p.298).

How do attracting and repelling chemicals in the environment pass signals across the cell membranes to bring about these responses? Recently, a three-year-old hypothesis that the protein called CheY interacs with another protein in the molecular motor to cause clockwise rotation was strongly confirmed by Philip Matsumura of the University of Illinois in Chicago and Shoshana Ravid and Michael Eisenbach, both of the Weizmann Institute of Science in Rehovot, Israel. Their findings appear in the October PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol. 83, No. 19).

Unlike earlier research done with whole bacteria, these studies were done with only the cellular envelopes including the five to eight flagella. By removing cytoplasm from the experimental setup, Matsumura says, he and his colleagues side-stepped a menagerie of biochemicals that would otherwise obscure interpretations of results. The researchers tethered the envelopes to glass that had been coated with flagella-grabbing antibodies. With a microscope, they could see which way the envelopes were turning.

When the scientists put enough CheY into the liquid medium containing envelopes rotating counterclockwise, rotation would become clockwise. Envelopes already rotating clockwise did not reverse their direction. Also, when the medium exceeded a certain level of acidity, clockwise rotation could not occur even when CheY was present. Yet when acidity was lowered, clockwise rotation resumed.

These findings, says Matsumura, confirm that CheY acts on the protein "switch" responsible for clockwise rotation and also provide some clues to the general question of how chemical signals prompt cellular behavior.