Programmable RNA and other recent advances in synthetic biology

There were 50-100 attendees at the Cell Press-sponsored Synthetic Biology conference at the University of California, San Francisco held on December 14, 2011. There was the usual acknowledgment of the field’s status (early-stage), potential impact (considerable), and articulation of what is needed (easy-to-use tools, reliable at-scale design and manufacturing processes, and standardized interoperable parts libraries) that has been typical at group gatherings (e.g.; SB 5.0) for the last few years. Also the point about a better marketing approach to attract scientists and public support to the field, something more enticing than the admittedly deadpan…

We pipette colorless liquids from one tube to another … we’re trying to cure cancer and change the world.

What was different was the degree of sophistication in the approaches, the easy multi-disciplinarity that researchers are bringing to the field, a more comprehensive understanding of the constituent materials (for example, the 5’ DNA does a lot of things: degradation, elongation, binding, etc. in a dynamic system where different processes come online to change resource use per osmolarity, temperature, etc.), and the contemplation of process portability across model organisms, for example from yeast to mammalian cells. The conference structure focused on the overall status and issues of the industry in a panel with leading scientists, and had talks regarding foundational technologies and applications.

Key points made by synthetic biology visionary Drew Endy (Stanford)

• Biology is the best manufacturing partner we’ll find, it has taken over the earth; biology is interesting as both a type of inquiry (we don’t understand everything yet) and as a building material
• Design experts (e.g.; from RSID, the New School, etc.) should be brought into biological design
• Bio-manufacturing is big, but storing data in cells could be bigger
• Metrology advances are needed, in units, reference standards, etc.; for example when shipping a gene expression module to colleagues in Shenzhen, what units should be employed?
• 4-D space-time programming languages is an important new area, only six people worldwide are thinking about this so far
• We need to do regenerative medicine without scaffolds, we know biological cells can differentiate into 3-D, how can we engineer this to happen?
• Synthetic biology needs to expand beyond the few workhorse chemicals used all the time like theophylline and tetracycline
• An important application area is drug design since small molecules, the main current paradigm used in drug development, are limited by their surface area, where they can travel to in the body, and other internal properties

Key conference themes

RNA as a programmable material
Programmable materials are an important input to synthetic biology as they may allow ongoing control over the dynamic processes of living cells. RNA is exemplar as a programmable substrate since it can be used to sense the presence of small molecules in cells and control gene expression by influencing which proteins are made and many other cellular activities [1]. In the keynote talk, Gerald Joyce (Scripps) discussed the specifics of exploiting RNA with a technique analogous to PCR (polymerase chain reaction), where an exponential number of copies of DNA are made to trigger desired cellular behaviors. In this case, an exponential number of copies of certain ligands (building-block molecules that bind with other molecules to trigger reactions in cells) are made that a certain enzyme-making RNA binds to for carrying out a desired cellular function [2].

Not only can RNA be used on a unitary basis to direct cellular actions, it can also be used as a component in constructing gene networks that serve as sophisticated molecular control devices like switches and circuits. Christina Smolke (Stanford) presented research using RNA to build synthetic controllers, for example a ribozyme-based device that can be used to detect metabolites non-invasively, a ribosome binding site-based device that can degrade harmful chemicals into neutral products, and a splicing-based device that can be used to target cell death [3]. A potential application was discussed using a synthetic RNA device to regulate cell signaling and T-cell proliferation in mammalian cells [4]. Alan Arkin (UC Berkeley and LBNL) suggested desirable ways to increase the complexity of synthetically generated devices, for example, assembling complexity from the constituent properties of the materials that is modular or context-free in deployment, and by having diverse RNA control elements on a single transcript [5]. This could also make devices more replicable.

Manipulating organelles
After the theme of RNA as a programmable material and synthetic genetic network regulatory element, another de facto theme was the capability to manipulate organelles.

David Savage (UC Berkeley) presented work regarding carboxysomes (protein-enclosed bacterial organelles). Synthetic organelles could be constructed that would be useful for a variety of cellular activities, including improving on current biological processes like RuBisCO leakage (an enzyme involved in the first major step of carbon fixation). Synthetic organelles could be developed based on previous work characterizing carboxysomes with shell and cargo fluorescent tagging [6], and recent work improving the stability and well-formedness of shells through shell-protein modification, particularly by adding a novel protein, CsoS1D, discovered by Cheryl Kerfeld’s lab (UC Berkeley and LBNL) [7,8].

Wallace Marshall (UCSF) discussed the importance of understanding and controlling organelle size, shape, and composition, the trade-offs between lipid and starch storage and controlled metabolism, for example. Tuning flagellar length could be important in the understanding and remedy of ciliary diseases [9], and experimental research suggested in one case that the quantity of LF4 (long flagella) protein being injected could be the key fulcrum of the control system. Organelle-tuning could have a broad range of useful applications, for example tuning up and down the ability of vacuoles to tolerate toxic compounds.

Applying synthetic biology to drug design
Michelle Chang (UC Berkeley) pointed out how the toxicity of fluorine makes it useful in drugs, and perhaps synthetic biology techniques could improve its effectiveness. A naturally-occurring fluorine-specific enzyme (FIK) was examined that demonstrated dramatic improvement in recognizing molecules [10]. Leor Weinberger (Gladstone Institute and UCSF) discussed synthetic viral circuits called therapeutic interfering particles (TIPs) that have been shown to reduce HIV/AIDS infection rates. The TIPs replicate conditionally in the presence of the pathogen and spread between individuals [11].

Developing foundational technologies
Hana El-Samad (UCSF) discussed the benefits of using hybrid biological and computer-based systems, where software algorithms were used to control a gene expression circuit’s behavior in real-time through a light-responsive module [12].

John Dueber (UC Berkeley) discussed the benefits of controlling the volume of enzymes expressed in cells, optimizing flux through cells. A desirable tool for this is combinatorial libraries to manage expression in multi-gene pathways. Further, when there are flux limitations in the pathway that cannot be managed with gene expression, there has been some interesting work building synthetic scaffolds to co-locate pathway enzymes around the areas of interest [13].

Nathan Hillson (LBNL) presented ways to automate and speed up the engineering cycle (design-build-test) with a component repository, selected components, and assembled components. Software design automation for assembly tools were discussed such as the JBEI-ICE repository platform and the GLAMM design tool.


References

1. Liu CC, Arkin AP. The case for RNA. Science. 2010 Nov 26;330(6008):1185-6.
2. Lam BJ, Joyce GF. An isothermal system that couples ligand-dependent catalysis to ligand-independent exponential amplification. J Am Chem Soc. 2011 Mar 9;133(9):3191-7.
3. Liang JC, Bloom RJ, Smolke CD. Engineering biological systems with synthetic RNA molecules. Mol Cell. 2011 Sep 16;43(6):915-26.
4. Chen YY, Jensen MC, Smolke CD. Genetic control of mammalian T-cell proliferation with synthetic RNA regulatory systems. Proc Natl Acad Sci U S A. 2010 May 11;107(19):8531-6.
5. Lucks JB, Qi L, Mutalik VK, Wang D, Arkin AP. Versatile RNA-sensing transcriptional regulators for engineering genetic networks. Proc Natl Acad Sci U S A. 2011 May 24;108(21):8617-22.
6. Savage DF, Afonso B, Chen AH, Silver PA. Spatially ordered dynamics of the bacterial carbon fixation machinery. Science. 2010 Mar 5;327(5970):1258-61.
7. Roberts EW, Cai F, Kerfeld CA, Cannon GC, Heinhorst S. Isolation and Characterization of the Prochlorococcus Carboxysome Reveals the Presence of the Novel Shell Protein CsoS1D. J Bacteriol. 2011 Dec 9.
8. Klein MG, Zwart P, Bagby SC, Cai F, Chisholm SW, Heinhorst S, Cannon GC, Kerfeld CA. Identification and structural analysis of a novel carboxysome shell protein with implications for metabolite transport. J Mol Biol. 2009 Sep 18;392(2):319-33.
9. Wemmer KA, Marshall WF. Flagellar length control in chlamydomonas--paradigm for organelle size regulation. Int Rev Cytol. 2007;260:175-212.
10. Weeks AM, Coyle SM, Jinek M, Doudna JA, Chang MC. Structural and biochemical studies of a fluoroacetyl-CoA-specific thioesterase reveal a molecular basis for fluorine selectivity. Biochemistry. 2010 Nov 2;49(43):9269-79.
11. Metzger VT, Lloyd-Smith JO, Weinberger LS. Autonomous targeting of infectious superspreaders using engineered transmissible therapies. PLoS Comput Biol. 2011 Mar;7(3):e1002015.
12. Milias-Argeitis A, Summers S, Stewart-Ornstein J, Zuleta I, Pincus D, El-Samad H, Khammash M, Lygeros J. In silico feedback for in vivo regulation of a gene expression circuit. Nat Biotechnol. 2011 Nov 6;29(12):1114-6.
13. Whitaker WR, Dueber JE. Metabolic pathway flux enhancement by synthetic protein scaffolding. Methods Enzymol. 2011;497:447-68.

Bio-design automation and synbio tools

The ability to write DNA could have an even greater impact than the ability to read it. Synthetic biologists are developing standardized methodologies and tools to engineer biology into new and improved forms, and presented their progress at the first-of-its-kind Bio-Design Automation workshop (agenda, proceedings) in San Francisco, CA on July 27, 2009, co-located with the computing industry’s annual Design Automation Conference. As with many areas of technological advancement, the requisite focus is on tools, tools, tools! (A PDF of this article is available here.)


Experimental evidence has helped to solidify the mindset that biology is an engineering substrate like any other and the work is now centered on creating standardized tools that are useful and reliable in an experimental setting. The metaphor is very much that of computing: just as most contemporary software developers work at high levels of abstraction and need not concern themselves with the 1s and 0s of machine language, in the future, synthetic biology programmers would not need to work directly with the Ac, Cs, Gs and Ts of DNA or understand the architecture of promoters, terminators, open reading frames and such. However, with synthetic biology being in its early stages, the groundwork to define and assemble these abstraction layers is currently at task.

Status of DNA synthesis
At present, the DNA synthesis process is relatively unautomated, unstandardized and expensive ($0.50-$1.00 per base pair (bp)); it would cost $1.5-3 billion to synthesize a full human genome. Synthesized DNA, which can be ordered from numerous contract labs such as DNA 2.0 in Menlo Park, CA and Tech Dragon in Hong Kong, has been following Moore’s Law (actually faster than Moore’s Law Carlson Curves doubling at 2x/yr vs. 1.5x/yr), but is still slow compared to what is needed. Right now short oligos, oligonucleotide sequences up to 200 bp, can be reliably synthesized but a low-cost repeatable basis for genes and genomes extending into the millions of bp is needed. Further, design capability lags synthesis capability, being about 400-800-fold less capable and allowing only 10,000-20,000 bp systems to be fully forward-engineered at present.

So far, practitioners have organized the design and construction of DNA into four hierarchical tiers: DNA, parts, devices and systems. The status is that the first two tiers, DNA and parts (simple modules such as toggle switches and oscillators), are starting to be consistently identified, characterized and produced. This is allowing more of an upstream focus on the next two tiers, complex devices and systems, and the methodologies that are needed to assemble components together into large-scale structures, for example those containing 10 million bp of DNA.

Standardizing the manipulation of biology
A variety of applied research techniques for standardizing, simulating, predicting, modulating and controlling biology with computational chemistry, quantitative modeling, languages and software tools are under development and were presented at the workshop.

Models and algorithms
In the models and algorithms session, there were some examples of the use of biochemical reactions for computation and optimization, performing arithmetic computation essentially the same way a digital computer would. Basic mathematical models such as the CME (Chemical Master Equation) and SSA (Stochastic Simulation Algorithm) were applied and extended to model, predict and optimize pathways and describe and design networks of reactions.

Experimental biology
The experimental biology session considered some potential applications of synthetic biology, first the automated design of synthetic ribosome binding sites to make protein production faster or slower (finding that the translation rate can be predicted if the Gibbs free energy (delta G) can be predicted). Second, an in-cell disease protection mechanism was presented where synthetic genetic controllers were used to prevent the lysis normally occurring in the lysis-lysogeny switch turned on in the disease process (lysogeny is the no-harm state and lysis is the death state).

Tools and parts
In the tools and parts session, several software-based frameworks and design tools were presented, many of which are listed in the software tools section below.

Languages and standardization
The languages and standardization session had discussions of language standardization projects such as the BioStream language, PoBol (Provisional BioBrick Language) and the BioBrick Open Language (BOL).

Software tools: a SynBio CrunchUp
Several rigorous computer-aided design and validation software tools and platforms are emerging for applied synthetic biology, many of which are freely available and open-source.

• Clotho: An interoperable design framework supporting symbol, data model and data structure standardization; a toolset designed in a platform-based paradigm to consolidate existing synthetic biology tools into one working, integrated toolbox
• SynBioSS - Synthetic Biology Software Suite: A computer-aided synthetic biology tool for the design of synthetic gene regulatory networks; computational synthetic biology
• RBS Calculator: A biological engineering tool that predicts the translation initiation rate of a protein in bacteria; it may be used in Reverse Engineering or Forward Engineering modes
• SeEd - Sequence Editor (work in progress): A tool for designing coding sequence alterations, a system conceptually built around constraints instead of sequences
• Cellucidate: A web-based workspace for investigating the causal and dynamic properties of biological systems; a framework for modeling modular DNA parts for the predictable design of synthetic systems
• iBioSim: A design automation software for analyzing biochemical reaction network models including genetic circuits, models representing metabolic networks, cell-signaling pathways, and other biological and chemical systems
• GenoCAD: An experimental tool for building and verifying complex genetic constructs derived from a library of standard genetic parts
• TinkerCell: A computer-aided design software for synthetic biology

Future of BioCAD
One of the most encouraging aspects in the current evolution of synthetic biology is the integrations the field is forging with other disciplines, particularly electronics design and manufacture, DNA nanotechnology and bioinformatics.

Scientists are meticulously applying engineering principles to synthetic biology and realize that novel innovations are also required since there are issues specific to engineering biological systems. Some of these technical issues include device characterization, impedance, matching, rules of composition, noise, cellular context, environmental conditions, rational design vs. directed evolution, persistence, mutations, crosstalk, cell death, chemical diffusion, motility and incomplete biological models.

As it happened in computing, and is happening now in biology, the broader benefit of humanity having the ability to develop and standardize abstraction layers in any field can be envisioned.

Clearly there will be ongoing efforts to more granularly manipulate and create all manner of biology and matter. Some of the subsequent areas where standards and abstraction hierarchies could be useful, though not immediate, are the next generations of computing and communications, molecular nanotechnology (atomically precise matter construction from the bottom up), climate, weather and atmosphere management, planet terraforming and space colony construction.

(Image credits: www.3dscience.com, www.biodesignautomation.org)

Status of life sciences

Right now is an exciting time in life sciences. The field is advancing, growing and changing in nearly every dimension, not just content-wise but also structure-wise. Tremendous content is coming forth in the form of key research findings, affordable new technologies and simultaneous holistic and reductionist expansions via systems biology approaches and new sub-field branching. Structure-wise, life science is changing in three important ways: the concept of life science, how science is conducted and the models by which health and health care are understood and realized.

Conceptually over time, life sciences have transitioned from being an art to a science to an information technology problem to now, an engineering problem. The way science is conducted is also shifting. Science 1.0 was investigating and enumerating physical phenomenon and doing hypothesis-driven trial and error experimentation. Science 2.0 adds two additional steps to the traditional enumeration and experimentation to create a virtuous feedback loop: mathematical modeling and software simulation, and building actual samples in the lab using synthetic biology and other techniques.

A second aspect of Science 2.0 is the notion of being in a post-scientific society, where innovation is occurring in more venues, not just government and industrial research labs but increasingly at technology companies, startups, small-team academic labs and in the minds of creative individual entrepreneurs.