9722781 Cusanovich Photoactive Yellow Protein (PYP) is a small soluble protein whose three-dimensional structure has been determined to high resolution. It appears to function as a blue light biosensor in the negative photoactic response of halopilic photosynthetic bacteria. It has a photocycle remarkably similar to those of bacteriorhodopsin and its homologs, although PYP is unrelated in structure to these membrane-spanning proteins. The long-term goal of this project is to elucidate the molecular details of the PYP photocycle as they relate to protein and chromophore structure. To accomplish this goal three general lines of study will be pursued: (1) Active site mutant proteins having altered spectra and photocycle kinetics will be prepared; (2) Structurally modified chromophores will be incorporated into wild type and mutant proteins in place of natural ones; (3) These two approaches will be combined by engineering an active site which will accommodate larger chromophores. The structural, thermodynamic, kinetic, and optical properties of the native and altered proteins will be investigated to understand the absorption and subsequent structural changes driven by light. As a light sensory system PYP has many properties in common with other less easily studied systems, such as bacteriorhodopsin and the visual pigment rhodopsin found in animals. In biological sensory systems responsive to light the protein portion of the molecule interacts with a pigment (for example, retinol in the human visual system) to define the wavelength or color of light which results in a biological response. The proposed studies with PYP will determine how the protein modulates the color of light detected. In addition, following the absorption of light by a photoactive sensory protein a series of events are initiated which lead to the biological response (for example the transmission of a signal to the brain in the visual process). PYP offers the opportunity to understand the light-induced structural changes which lead to biological recognition. Finally PYP has properties that make it a candidate as a biomaterial for use as bioelectronic devices (for example, a switch or computer memory) which may have applications in the next generation of electronic devices. ***
