Preferential Binding of a Chlorophyll Derivative by a Water-Soluble Chlorophyll Protein Mutant

In the photosynthetic process, pigment-protein complexes use vibrational-electronic (vibronic) coupling to efficiently transfer energy from where light energy is absorbed to the reaction center. This vibronic coupling is the source of much interest because if it can be better understood, it can be applied to creating systems with customizable energy gaps and provide additional insights into energy transfer processes. The water-soluble chlorophyll protein (WSCP) of Lepidium virginicum is a useful model system for this research because it binds only four chlorophyll pigments in a symmetric “dimer-of-dimers” arrangement. Previous work has shown that single-point mutations of WSCP can predictably shift the wavelength of maximum absorption. During that project, the T52K mutant showed an unexpectedly large shift from 671 nm to 645 nm. This work investigates the cause of that shift and proposes that T52K has a unique binding affinity for the chlorophyll derivative C132-hydroxy-chlorophyll a.