Abstract
Blue copper proteins share a highly conserved type-1 copper coordination that gives rise to characteristic spectroscopic signatures, yet they are embedded in evolutionarily divergent protein folds. Here, we investigate how differences in protein architecture modulate ultrafast electronic and vibrational relaxation following optical excitation of the blue copper site. Using transient absorption spectroscopy, we compare the excited-state dynamics of two evolutionarily distant proteins: the single-domain electron-transfer protein azurin and two-domain small laccase (SLAC) belonging to the family of multicopper oxidases. Kinetic analysis of the transient spectra reveals coherent vibrational wave packets generated via impulsive stimulated Raman scattering, providing access to low-frequency collective modes associated with the electronic ground state. Notably, distinct dominant modes are observed for the two proteins, centered at 38 cm(-1) for SLAC and 29 cm(-1) for azurin. These differences are correlated with variations in structural rigidity and coordination constraints beyond the first coordination spheres of the blue copper site. Our results reveal that, despite conserved metal coordination, the surrounding protein arrangement plays a significant role in shaping ultrafast energy relaxation pathways in metalloprotein.