Global Landscape of Native Protein Complexes in Synechocystis sp. PCC 6803.

Synechocystis sp. PCC 6803 (hereafter: Synechocystis) is a model organism for studying photosynthesis, energy metabolism, and environmental stress. Though known as the first fully sequenced phototrophic organism, Synechocystis still has almost half of its proteome without functional annotations. In this study, we used co-fractionation and liquid chromatography-tandem mass spectrometry (LC/MS/MS) to define 291 multi-protein complexes, encompassing 24,092 protein-protein interactions (PPIs) among 2062 distinct gene products. This information not only revealed the roles of photosynthesis in metabolism, cell motility, DNA repair, cell division, and other physiological processes, but also showed how protein functions vary from bacteria to higher plants due to changes in interaction partners. It also allowed us to uncover the functions of hypothetical proteins, such as Sll0445, Sll0446, and Sll0447, participating in photosynthesis and cell motility, and Sll1334 in regulating fatty acid biogenesis. Here we present the most extensive protein interaction data for Synechocystis so far, which provides critical insights into fundamental molecular mechanisms in Cyanobacterium.