Autoinhibitory mechanism and activity-related structural changes in a mycobacterial adenylyl cyclase

Barathy, Deivanayaga V and Bharambe, Nikhil G and Syed, Wajeed and Zaveri, Anisha and Visweswariah, Sandhya S and Colaco, Melwin and Misquith, Sandra and Suguna, Kaza (2015) Autoinhibitory mechanism and activity-related structural changes in a mycobacterial adenylyl cyclase. In: JOURNAL OF STRUCTURAL BIOLOGY, 190 (3). pp. 304-313.

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Abstract

An adenylyl cyclase from Mycobacterium avium, Mal 120, is a functional orthologue of a pseudogene Rv1120c from Mycobacterium tuberculosis. We report the crystal structure of Mal 120 in a monomeric form and its truncated construct as a dimer. Mal 120 exists as a monomer in solution and crystallized as a monomer in the absence of substrate or inhibitor. An additional alpha-helix present at the N-terminus of the monomeric structure blocks the active site by interacting with the substrate binding residues and occupying the dimer interface region. However, the enzyme has been found to be active in solution, indicating the movement of the helix away from the interface to facilitate the formation of active dimers in conditions favourable for catalysis. Thus, the N-terminal helix of Ma1120 keeps the enzyme in an autoinhibited state when it is not active. Deletion of this helix enabled us to crystallize the molecule as an active homodimer in the presence of a P-site inhibitor 2',5'-dideoxy-3'-ATP, or pyrophosphate along with metal ions. The substrate specifying lysine residue plays a dual role of interacting with the substrate and stabilizing the dimer. The dimerization loop region harbouring the second substrate specifying residue, an aspartate, shows significant differences in conformation and position between the monomeric and dimeric structures. Thus, this study has not only revealed that significant structural transitions are required for the interconversion of the inactive and the active forms of the enzyme, but also provided precise nature of these transitions. (C) 2015 Elsevier Inc. All rights reserved.

Item Type:	Journal Article
Publication:	JOURNAL OF STRUCTURAL BIOLOGY
Publisher:	ACADEMIC PRESS INC ELSEVIER SCIENCE
Additional Information:	Copy right for this article belongs to the ACADEMIC PRESS INC ELSEVIER SCIENCE, 525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA
Keywords:	Crystal structure; Adenylyl cyclase; 2 `,5 `-Dideoxy-3 `-adenosine triphosphate; Homodimer; Pyrophosphate; cAMP
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit Division of Biological Sciences > Molecular Reproduction, Development & Genetics
Date Deposited:	19 Jul 2015 09:38
Last Modified:	19 Jul 2015 09:38
URI:	http://eprints.iisc.ac.in/id/eprint/51881

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