1. Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
2. Present address: Department of Chemistry, Pennsylvania State University, University Park, PA, USA.
3. Department of Chemistry, Portland State University, Portland, OR, USA
4. Present address: Zymergen, Inc., 1650 65th Street, Emeryville, CA 94608, USA.
5. Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR, USA