Surface-Enhanced Raman Scattering Captures Conformational Changes of Single Photoactive Yellow Protein Molecules under Photoexcitation

Distinct conformational changes of single photoactive yellow protein (PYP) molecules were captured under photoexcitation, using a SERS substrate approach. These steps conform to those in PYP's photocycle. At the single molecule level, SERS of PYP yields well-resolved peaks, some of which were not reported earlier. Further, exclusive peak pairs have been identified that can elucidate PYP's conformational steps and chemisorption configuration on Ag using the SERS selection rules. Despite the "weak chemisorption" of PYP on silver that only allows the single molecule signal to sustain for approximately 1 s, this duration may be long enough to resolve PYP's photocycle (approximately 0.3 s).