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A recent phylogenetic analysis has shown that the genus Stephanopis comprises several different lineages of bark-dweller crab spiders. The ones with South American distribution that present a close relationship with other Neotropical genera like Epicadus, Onocolus, Rejanellus and Epicadinus were recovered in a single clade, with good support and stability. Here, we present a taxonomic review of Stephanopis species attributed to the ‘pentacantha clade’, proposing the new genus Kryptochroma Machado gen. nov. to accommodate them. New distribution records are provided and the following species are described for the first time: Kryptochroma gigas Machado & Viecelli gen. et sp. nov., Kryptochroma hilaris Machado & Teixeira gen. et sp. nov., Kryptochroma quadrata Machado & Viecelli sp. nov. and Kryptochroma septata Machado & Teixeira sp. nov. The species Stephanopis borgmeyeri is considered a nomen dubium, Stephanopis aheneus is a junior synonym of Epicadus tuberculatus, Stephanopis quimiliensis is transferred to Ulocymus and Stephanopis stelloides is transferred to Epicadus, being Epicadus stelloides the senior synonym of Stephanopis salobrensis, Stephanopis trilobata and Epicadus caudatus.
Electron transfer in respiratory chains generates the electrochemical potential that serves as energy source for the cell. Prokaryotes can use a wide range of electron donors and acceptors and may have alternative complexes performing the same catalytic reactions as the mitochondrial complexes. This is the case for the alternative complex III (ACIII), a quinol:cytochrome c/HiPIP oxidoreductase. In order to understand the catalytic mechanism of this respiratory enzyme, we determined the structure of ACIII from Rhodothermus marinus at 3.9 Å resolution by single-particle cryo-electron microscopy. ACIII presents a so-far unique structure, for which we establish the arrangement of the cofactors (four iron–sulfur clusters and six c-type hemes) and propose the location of the quinol-binding site and the presence of two putative proton pathways in the membrane. Altogether, this structure provides insights into a mechanism for energy transduction and introduces ACIII as a redox-driven proton pump.