MpcT is the transducer for membrane potential changes in Halobacterium salinarum

Area of Science:

• Microbiology
• Cellular Biology
• Biophysics

Background:

• Halobacterium salinarum utilizes light-driven ion pumps like bacteriorhodopsin and halorhodopsin.
• These bacteria exhibit phototaxis, a directional movement in response to light.
• Signal transduction pathways converting environmental stimuli into cellular responses are crucial for bacterial adaptation.

Purpose of the Study:

• To identify the specific transducer protein responsible for mediating phototaxis in H. salinarum mutants lacking other retinal proteins.
• To elucidate the precise environmental signal (membrane potential or pH change) that triggers the phototactic response.
• To characterize the function and properties of the identified transducer.

Main Methods:

• Deletion analysis of 18 known and putative halobacterial transducer (htr) genes in H. salinarum.
• Mutant strain construction and phototaxis assays under controlled irradiance.
• Measurement of cytoplasmic buffering capacity and minimal stimulus length for response initiation.

Main Results:

• Htr14, a methylatable membrane-bound transducer, was identified as the key mediator of phototaxis.
• The biological response, including adaptive methylation, is dependent on Htr14.
• The study concluded that changes in membrane potential (DeltaPsi), not internal pH, serve as the primary signal for phototaxis.

Conclusions:

• Htr14 was renamed Membrane potential change Transducer (MpcT) to reflect its specific function.
• MpcT is the first identified transducer directly activated by changes in membrane potential (DeltaPsi).
• This finding provides novel insights into sensory mechanisms and signal transduction in archaea.