Functional comparison of EncB and EncC cargo proteins in iron storage within the Myxococcus xanthus encapsulin.

Encapsulins are self-assembling protein nanocompartments that selectively encapsulate cargo proteins to perform specialized functions. The Myxococcus xanthus encapsulin system incorporates three cargo proteins, of which EncB and EncC are classified as ferritin-like proteins with ferroxidase activity; however, their functional distinction remains unclear. Here, we investigate the individual contributions of EncB and EncC to iron mineralization within the encapsulin shell. We show that EncB and EncC produce iron-containing minerals with differing phosphorus content and that reducing the number of cargo proteins increases ferrous iron influx into the encapsulated mineral core. These findings provide the first functional comparison of two ferritin-like co-encapsulated cargo proteins and suggest that cargo composition may allow fine-tuning of mineral properties in response to cellular requirements.