Control of Protein Self-Assembly with Water-Soluble Porphyrins

Abstract

Interactions between charged porphyrins and complimentary or similarly charged proteins provide important models systems for studies of electron transfer processes, artificial photosynthesis, and control of protein-protein interactions. Typically, the experimental results are analyzed and discussed assuming that the proteins exist in a monodisperse state. Here, we explored interaction of wild-type and 12 mutants of PpcA, a 3-heme c-type cytochrome (cyt) from Geobacter sulfurreducenswith several anionic water-soluble derivatives of tetraphenylporphyrin. Combined small- and wide-angle X-ray scattering experiments revealed formation of multimers with a wide range of complex sizes. Thermodynamic interaction parameters and complex binding stoichiometries were established with isothermal calorimetry. All-atom molecular dynamics simulations revealed quick complex formation with binding sites well matching the areas identified in our experimental work. The obtained results demonstrate that multimerization of solution-state proteins by large water-soluble ligands can be tuned to control shape and size of the formed complexes. Molecular level mapping of the binding sites allows us to build a theory explaining the size of the formed complexes and provides opportunities for targeted design and assembly of multi-subunit protein complexes.