Solvent penetration in photoactive yellow protein R52Q mutant: A theoretical study

An R52Q mutation of photoactive yellow protein creates a cavity mimicking an intermediate state in the wild-type. This mutation, of a positively charged arginine to a neutral glutamine, does not affect the spectral tuning of photoactive yellow protein. Contradicting explanations for this phenomenon suggest either water or hydronium occupation in the cavity. To solve this controversy, we have performed 3D-RISM calculations on the mutant structure examining the solvation structure. Our results show that while there is a high probability of hydronium in the cavity compared to bulk, there is still a relatively low occupation when considering realistic concentrations. Thus our findings suggest that while the cavity is clearly accessible by hydronium, it is mostly occupied by water molecules. We expect high-resolution neutron crystallographic analysis of the mutant to confirm our prediction.