A Synthetic Enzymatic Pathway for Hydrogen Production from Starch

Zhang, et al., demonstrate a synthetic pathway consisting of 13 enzymes that turns starch into hydrogen.  The paper, at PLoSone, makes clear how important it is to ensure that the definition of Synthetic Biology, if there is a definition yet, includes not just new circuits in cells and new organisms but also cell free systems.  The article (High-Yield Hydrogen Production from Starch and Water by a Synthetic Enzymatic Pathway) is open access, so I won't bother to quote from it extensively.

But the details are pretty cool.  The authors used 11 off-the-shelf enzymes (from spinach, rabbit, E. coli, and yeast) ordered from Sigma, and two they purified themselves (from coli, and P. furiosus).  I imagine it won't be too long before those last two are also available commercially. Here is a paragraph that sums up the context of what the authors accomplished and where they will look for performance improvements:

This robust synthetic enzymatic pathway that does not function in nature was assembled by 12 mesophilic enzymes from animal, plant, bacterial, and yeast sources, plus an archaeal hyperthermophilic hydrogenase. The performance (e.g., reaction rate and enzyme stability) is anticipated to be improved by several orders of magnitude by using the combination of (a) enzyme component optimization via metabolic engineering modeling, (b) interchangeable substitution of mesophilic enzymes by recombinant thermophilic or even hyperthermophilic enzymes, (c) protein engineering technologies, and (d) higher concentrations of enzymes and substrates. ... This research approach will naturally benefit from on-going improvements by others in synthetic biology systems that are addressing cofactor stability, enzyme stability by additives, and co-immobilization, and development of minimal microorganisms that can be built upon to create an in vivo enzyme system that produces H2 in high yields.

What I think is most interesting about all this is that Zhang and colleagues have effectively just put a whole bunch of new Biobricks on the table.  Moreover, those new parts for producing biofuels are reasonably well characterized, at least in vitro.  A cursory search of the Registry of Standard Biological Parts doesn't turn up any of these enzymes, but since the gene sequences are either already in Genbank or are relatively easy to generate, this gap points to an area of expansion for Biobricks in general and the International Genetically Engineered Machines Competition (iGEM) in particular.

I suggest it is time to expand the horizons of iGEM beyond demonstration projects to start tackling real world problems.  The student teams have made fantastic progress over the past few years, with some projects winding up on the cover of high-profile journals.  I would like to see this year's iGEM participants take on biological production of fuels and materials, bioremediation, and biological carbon sequestration.  Even if popular attention has yet to come round, the problems we presently face are enormous (see my post "It's Time to Invest in Water Wings"), and through the combination of enthusiasm and creativity iGEM participants could start developing solutions today.