The role of Ca ²⁺ and protein scaffolding in the formation of nature’s water oxidizing complex

Abstract

Significance Unlike cofactor insertion into other metalloproteins, assembly of the photosynthetic water oxidation complex of photosystem II (PSII) in plants, algae, and cyanobacteria is a light-driven process that photooxidatively incorporates Mn 2+ and Ca 2+ ions into the protein matrix forming the catalytic Mn 4 CaO 5 metal cluster. This self-assembly process is important both for de novo biogenesis and for the frequent repair of PSII due to its susceptibility to photodamage. While the basic kinetic scheme for this process was established nearly 50 y ago, the molecular details have remained enigmatic. Here we describe results on the role of inorganic and protein cofactors and integrate them with previous information to obtain an important upgrade in our understanding of this process.