Methods for producing microcompartments
To produce a bacterial microcompartment shell, or a designed shell based on naturally occurring bacterial microcompartment shells in a new host organism, a synthetic operon is constructed that contains the desired shell protein genes and translation efficiency is controlled by host specific ribosomal binding sites. Proteins or other molecules can be encapsulated in the microcompartment shells by various methods described herein. The constructs can also be used to express self-assembling sheets comprised of shell proteins.
1. A method for producing bacterial microcompartments in a prokaryotic host organism, said method comprising:
introducing into a prokaryotic host organism an expression vector comprising a heterologous nucleotide sequence comprising (a) an operably linked promoter that drives expression in the organism; (b) a first ribosomal binding site sequence that provides a first level of translation initiation and controls expression efficiency in the host organism of a first bacterial microcompartment gene that encodes a first protein comprising a single BMC domain, and (c) a second ribosomal binding site sequence different from the first ribosomal binding site sequence, wherein the second ribosomal binding site sequence provides a second level of translation initiation and controls expression efficiency in the host organism of each of three variants of a second bacterial microcompartment gene that encodes a second protein comprising two BMC domains derived from a bacteria for producing a bacterial microcompartment; and
incubating the prokaryotic host organism to produce the bacterial microcompartments,
wherein the second level of translation initiation is lower than the first level of translation initiation.
2. The method of claim 1 , wherein the host organism is a bacterial cell.
3. The method of claim 2 , wherein the host organism is E. coli or B. subtilis.
4. The method of claim 1 , wherein the expression vector comprises a polynucleotide comprising one or more hexamer genes, tandem domains, and pentamers.
5. The method of claim 1 , wherein the first and second bacterial microcompartment genes are heterologous for the host organism.
6. The method of claim 1 , wherein the promoter is an inducible promoter.
7. The method of claim 1 , wherein the promoter is contiguous to the first or second bacterial microcompartment gene.
8. The method of claim 1 , wherein the first or second ribosomal binding site sequence is derived from Escherichia coli or Halothiobacillus neapolitanus.
9. The method of claim 1 , wherein the first or second bacterial microcompartment gene encodes shell proteins derived from Haliangium ochraceum, Mycobacterium smegmatis , or Thermosynechococcus elongatus.
10. The method of claim 1 , wherein the expression vector further comprises a selectable marker gene.
11. The method of claim 10 , wherein the selectable marker gene is selected from a group consisting of an antibiotic resistance gene, β-galactosidase gene, and fluorescent protein gene.
12. The method of claim 1 , wherein the expression vector further comprises a polynucleotide encoding an encapsulating targeting peptide linked to a polynucleotide encoding a protein that provides enhanced metabolic activity in the host organism.
13. The method of claim 12 , wherein the encapsulating targeting peptide is located in the C-terminal or N-terminal region of the protein that provides enhanced metabolic activity in the host organism.
14. The method of claim 12 , wherein the enhanced metabolic activity comprises CO 2 fixation or alcohol breakdown.
15. The method of claim 1 , wherein the first protein and the three variants of the second protein are present in the bacterial microcompartment at a mass ratio of 3:1:1:1.
16. The method of claim 1 , wherein the first protein and the three variants of the second protein are present in the bacterial microcompartment at a molar ratio of 7:1:1:1.
17. The method of claim 1 , wherein the first protein and the three variants of the second protein are present in the bacterial microcompartment at a molar ratio of 8:1:1:1.
18. The method of claim 1 , wherein the expression vector further comprises a third ribosomal binding site sequence that provides a third level of translation initiation and controls expression efficiency in the host organism of a third bacterial microcompartment gene, wherein the third level of translation initiation is different from the first or second levels of translation initiation.