Abstract
Using a newly discovered encapsulin from Mycolicibacterium hassiacum, several biocatalysts were packaged in this robust protein cage. The encapsulin was found to be easy to produce as recombinant protein. Elucidation of its crystal structure revealed that it is a spherical protein cage of 60 protomers (diameter of 23 nm) with narrow pores. By developing an effective coexpression and isolation procedure, the effect of packaging a variety of biocatalysts could be evaluated. It was shown that encapsulation results in a significantly higher stability of the biocatalysts. Most of the targeted cofactor-containing biocatalysts remained active in the encapsulin. Due to the restricted diameters of the encapsulin pores (5–9 Å), the protein cage protects the encapsulated enzymes from bulky compounds. The work shows that encapsulins may be valuable tools to tune the properties of biocatalysts such as stability and substrate specificity.
Highlights
Compartmentalization of the cell’s interior to create distinct organelles is a defining hallmark of eukaryotes
We describe the structural features of an encapsulin originating from the mesothermophile Mycolicibacterium hassiacum (EncMh) and its use as protein cage for several biocatalysts
By analyzing its genome for encapsulin homologs we identified a small operon consisting of two genes encoding a putative encapsulin (EncMh, WP_005630281.1) and a putative DyP-type peroxidase (EKF22245.1)
Summary
Compartmentalization of the cell’s interior to create distinct organelles is a defining hallmark of eukaryotes. This provides these cells with a way to separate and optimize metabolic processes. While the reason for bringing together a selected set of enzymes within a protein shell is not always clear, bacterial microcompartments are conserved and widespread in the bacterial kingdom [1,2]. This strongly suggests that they are essential for proper functioning of the encapsulated enzymes. Encapsulation of enzymes within a protein cage can promote the reaction rate as a consequence of the high
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