Department of Biochemistry, Vanderbilt University, 2215 Garland Avenue, Nashville, TN 37212, USA.|Department of Civil and Environmental Engineering, University of California Irvine, 4130 Engineering Gateway, Irvine, CA 92697-2175, USA.|Department of Biochemistry, Vanderbilt University, 2215 Garland Avenue, Nashville, TN 37212, USA.