Exploring Novel Biophysical Mechanisms in Evolved Optical Systems

Many sophisticated biological processes can be understood using basic concepts from physics. With this approach in mind, I will present two novel biophysical mechanisms derived from optical systems in marine animals. I will begin by describing the physical mechanism used by giant clams to increase diffusive flux of photosynthetic product from symbiotic algae. Over 50 years ago, it was reported that the addition of clam homogenate to algae stimulated photosynthate release, but the molecular effectors and mechanism of this “host release factor” have remained unresolved. Here we show that zwitterionic betaines, long known to exist in millimolar concentrations in coral and clam hosts, generally accelerate photosynthate diffusion. The electric field emanating from these molecules serves to organize water and generate a chemical potential for diffusion of small, polar molecules such as glucose and glycerol. The rest of my dissertation is dedicated to characterizing the sequence, structure, and function of the reflectin protein. The reflectin protein is responsible for giving cephalopods the remarkable ability to manipulate incident light to camouflage with their environment. This unique capability is made possible by iridescent cells composed of over 90% reflectin protein. The highly evolutionarily conserved region of reflectin that is unique to cephalopods has proven intractable to most standard biophysical characterizations including crystallization. Using a combination of sequence analysis and molecular modeling, I will explore the structure of motifs and the regions of sequence that connect them in bulk water and at membrane interfaces. I will then discuss the development of an experimental system designed to probe the interactions between reflectin and lipids. Here we show that reflectin, known to self-assemble into dense, membrane bound platelets, strongly interacts with lipid bilayers and increases the propensity for the membrane to adopt the flat structures observed in cells