Synthetic Biology Parts, Devices and Applications

282 14 Sequestered: Design and Construction of Synthetic Organelles

Catalysis is often the motivating factor for organelle engineering, leading to

two linked properties – compartment permeability and its inherent chemical

environment. Permeability is the selectivity of the surrounding membrane or

protein shell that directly affects what can diffuse across or be transported in and

out of the compartment. In lipid‐based organelles, selectivity is modulated by

the nature of the membrane lipid content and types and specificities of integral

membrane transporters or channels. In proteinaceous organelles, it is simply a

function of the shell’s diffusive permeability. In a related context, the chemical

environment, set up by the interplay of both permeability and combined enzy­

matic activity taking place within the compartment, will control the concentra­

tions of potential substrates and products, as well as general properties such as

pH [23]. These concentrations will directly control both the thermodynamic

equilibrium of a particular process and its kinetics, profoundly shaping the cata­

lytic potential of an organelle.

Finally, it is important to have a working understanding of organelle biogenesis.

Biogenesis is the process of organelle self‐organizing and will control organelle

shape, size, and copy number [24]. Repurposing efforts focused on existing lipid‐

based organelles have so far shied away from extensive remodeling, but it is logi­

cal to assume future efforts will enable the complete refactoring of existing

structures or even the de novo creation of novel compartments. Engineered bio­

genesis has had more success in the protein‐based space, as the genetic informa­

tion required for synthesis is far less. BMCs contain roughly 10–15 proteins, and

there are established systems for the transgenic expression of microcompart­

ments in new organismal hosts.

In understanding these four properties, we therefore seek a deep understand­

ing of organelle structure and function. Put another way, the synthetic biology‐

minded goal of engineering novel organelles represents hypothesis testing to an

Permeability Protein targeting

Biogenesis

(self-assembling)

H+

·OH

Fe2+

Chemical

environment

Figure 14.2 Four core design principles for a synthetic organelle.