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Class III adenylyl cyclases usually possess six highly conserved catalytic residues. Deviations in these canonical amino acids are observed in several putative adenylyl cyclase genes as apparent in several bacterial genomes. This suggests that a variety of catalytic mechanisms may actually exist. The geneRv0386from Mycobacterium tuberculosiscodes for an adenylyl cyclase catalytic domain fused to an AAA-ATPase and a helix-turn-helix DNA-binding domain. | ềFEBS Journal Adenylyl cyclase Rv0386 from Mycobacterium tuberculosis H37Rv uses a novel mode for substrate selection Lucila I. Castro Corinna Hermsen Joachim E. Schultz and Jurgen U. Linder Abteilung Pharmazeutische Biochemie Fakultejt fur Chemie und Pharmazie Universitat Tubingen Germany Keywords Adenylylcyclase cyclic nucleotide guanylyl cyclase Mycobacterium tuberculosis substrate specificity Correspondence J. U. Linder Abteilung Pharmazeutische Biochemie Fakultat fur Chemie und Pharmazie Universitat Tubingen Morgenstelle 8 72076 Tubingen Germany Fax 49 7071 295952 Tel 49 7071 2974676 E-mail juergen.linder@uni-tuebingen.de Received 27 March 2005 revised 13 April 2005 accepted 18 April 2005 doi 10.1111 j.1742-4658.2005.04722.x Class III adenylyl cyclases usually possess six highly conserved catalytic residues. Deviations in these canonical amino acids are observed in several putative adenylyl cyclase genes as apparent in several bacterial genomes. This suggests that a variety of catalytic mechanisms may actually exist. The gene Rv0386 from Mycobacterium tuberculosis codes for an adenylyl cyclase catalytic domain fused to an AAA-ATPase and a helix-turn-helix DNA-binding domain. In Rv0386 the standard substrate adenine-defining lysine-aspartate couple is replaced by glutamine-asparagine. The recombinant adenylyl cyclase domain was active with a Vmax of 8 nmol cAMP-mg-1-min-1. Unusual for adenylyl cyclases Rv0386 displayed 20 guanylyl cyclase side-activity with GTP as a substrate. Mutation of the glutamineasparagine pair either to alanine residues or to the canonical lysine-aspar-tate consensus abolished activity. This argues for a novel mechanism of substrate selection which depends on two noncanonical residues. Data from individual and coordinated point mutations suggest a model for purine definition based on an amide switch related to that previously identified in cyclic nucleotide phosphodiesterases. The second messenger cAMP is synthesized by a large variety .
