(A) SIMBAL-identified residues making up the F420-binding surface of M. tuberculosis FGD1 (PDB accession no. 3B4Y [4]). Peak 1, SDH, is in contact with the carboxylate oxygens of the deazaflavin terminal ring (cyan). Peak 2, SVLT, includes the nonproline cis-peptide bond between serine and valine (2) and comprises the “bulge” behind the deazaflavin central ring (red). Peak 3, GTGE, is in contact with the phospholactate component of the side chain (yellow). Peak 4, FKER, is in contact with the single glutamate resolved by the crystal structure and forms a long adjacent surface cleft (blue). Peak 5, AAGGPAV, contacts the deazaflavin hydroxyl (obscured), the side chain phospholactate, and the carboxylate of the resolved side chain glutamate and also forms the putative polyglutamate binding cleft (green). (B) A patch of positively charged residues (blue) lines the poly-Glu binding cleft and is surrounded by a more distant ring of negatively charged residues (red). F420 is indicated as a stick model (green = carbon, red = oxygen, blue = nitrogen, and orange = phosphorus). Molecular models were visualized with MacPyMOL (http://pymol.org/).