Self-Assembly of Nanofilaments in Cyanobacteria for Protein Co-localization

Cyanobacteria offer
great potential as alternative biotechnological
hosts due to their photoautotrophic capacities. However, in comparison
to established heterotrophic hosts, several key aspects, such as product
titers, are still lagging behind. Nanobiotechnology is an emerging
field with great potential to improve existing hosts, but so far,
it has barely been explored in microbial photosynthetic systems. Here,
we report the establishment of large proteinaceous nanofilaments in
the unicellular model cyanobacterium Synechocystis sp. PCC 6803 and the fast-growing cyanobacterial strain Synechococcus elongatus UTEX 2973. Transmission electron
microscopy and electron tomography demonstrated that expression of pduA*, encoding a modified bacterial microcompartment shell
protein, led to the generation of bundles of longitudinally aligned
nanofilaments in S. elongatus UTEX 2973 and shorter
filamentous structures in Synechocystis sp. PCC 6803.
Comparative proteomics showed that PduA* was at least 50 times more
abundant than the second most abundant protein in the cell and that
nanofilament assembly had only a minor impact on cellular metabolism.
Finally, as a proof-of-concept for co-localization with the filaments,
we targeted a fluorescent reporter protein, mCitrine, to PduA* by
fusion with an encapsulation peptide that natively interacts with
PduA. The establishment of nanofilaments in cyanobacterial cells is
an important step toward cellular organization of heterologous pathways
and the establishment of cyanobacteria as next-generation hosts.