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Iron–sulfur (Fe–S) clusters play important roles in electron transfer, metabolic and biosynthetic reactions, and the regulation of gene expression. Understanding the biogenesis of Fe–S clusters is therefore relevant to many fields. In the complex process of Fe–S protein formation, the A-type assembly protein (ATAP) family, which consists of several subfamilies, plays an essential role in Fe–S cluster formation and transfer and is highly conserved across the tree of life. However, the taxonomic distribution, motif compositions, and the evolutionary history of the ATAP subfamilies are not well understood. To address these problems, our study investigated the taxonomic distribution of 321 species from a broad cross-section of taxa. Then, we identified common and specific motifs in multiple ATAP subfamilies to explain the functional conservation and nonredundancy of the ATAPs, and a novel, essential motif was found in Eumetazoa IscA1, which has a newly found magnetic function. Finally, we used phylogenetic analytical methods to reconstruct the evolution history of this family. Our results show that two types of ErpA proteins (nonproteobacteria-type ErpA1 and proteobacteria-type ErpA2) exist in bacteria. The ATAP family, consisting of seven subfamilies, can be further classified into two types of ATAPs. Type-I ATAPs include IscA, SufA, HesB, ErpA1, and IscA1, with an ErpA1-like gene as their last common ancestor, whereas type-II ATAPs consist of ErpA2 and IscA2, duplicated from an ErpA2-like gene. During the mitochondrial endosymbiosis, IscA became IscA1 in eukaryotes and ErpA2 became IscA2 in eukaryotes, respectively. [ABSTRACT FROM AUTHOR]

Protein crystallization screens are commonly used to find specific crystallization conditions. In practice, undesirable clear drops are often ignored. We hypothesize that clear drops may be potentially useful for finding the conditions leading to proteins with high solubility and monodispersity . Based on this idea, we first tested three model proteins and confirmed that improved monodispersity could be observed in the clear drops. Next, we used this strategy to achieve the maximum solubility and monodispersity of a new protein (RNA binding motif 3, RBM3). We suggest that this strategy is useful not only for high-throughput screening of optimal solubilization conditions but also for screening of biopharmaceutical formulations. [ABSTRACT FROM AUTHOR]