9zw3
Quasibacillus thermotolerans T=4 encapsulin pore mutant variant Letter11
Structural highlights
FunctionENCAP_BACTR Shell component of a type 1 encapsulin nanocompartment. Assembles into proteinaceous icosahedral shells 42-43 nm in diameter with an iron- and phosphorus-rich core (1Fe:1.1P) which can store over 23,000-35,000 iron atoms (with a calculated maximum of 83,000 Fe). There are 2 types of negatively charged open pores in the cryo-electron structure; a 3-fold pore where 3 hexamers meet with a minimal size of 7.2 Angstroms and a 5-fold pore where pentamers meet with a minimal size of 2.3 Angstroms. The 2-fold pore seen in other encapsulin nanocompartments is closed. Empty compartments can be generated in E.coli (PubMed:28263314, PubMed:31194509, PubMed:31282860). Both types of pore have extra density in their centers in the structure (PubMed:31282860). 2 different cargo proteins have been identified (IMEF and Fer); when both are expressed in E.coli with the shell protein only IMEF is detected within the nanocompartment. E.coli expressing all 3 genes stores the largest amount of iron and is protected from Fe/H2O2-induced oxidative stress (PubMed:28263314). Part of the iron-mineralizing encapsulin-associated Firmicute (IMEF) system (Probable).[1] [2] [3] [4] Publication Abstract from PubMedGene duplication has played a critical role in the evolutionary history of proteins, enabling complex multimers to emerge from simpler precursors. Yet in protein engineering, current methods for directed evolution do not exploit gene duplication, hampering access to the vast array of diverse variants that are only enriched in the presence of a wild-type copy. We establish a directed evolution strategy for multimeric proteins that harnesses gene duplication to compensate for metabolic burden and self-assembly fitness, allowing previously inaccessible variants to be enriched. Starting from a homomeric 240-mer capsid, gene duplication enables selection of both extreme homomeric variants and obligate heteromers. This strategy significantly expands engineering access to diverse high-performing variants, while also supporting a plausible model for evolutionary diversification of higher-order multimers in nature. Directed evolution of multimeric proteins is enabled by dual-compensatory gene duplication.,Siddiquee R, Lie F, Szyszka TN, Loustau A, Andreas MP, Giessen TW, Lau YH bioRxiv [Preprint]. 2026 Jan 12:2026.01.12.698938. doi: , 10.64898/2026.01.12.698938. PMID:41648261[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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