title: Comparative genomics of cyclic-di-GMP signalling in bacteria: post-translational regulation and catalytic activity.
abstract: Cyclic-di-GMP is a bacterial second messenger that controls the switch between motile and sessile states. It is synthesized by proteins containing the enzymatic GGDEF domain and degraded by the EAL domain. Many bacterial genomes encode several copies of proteins containing these domains, raising questions on how the activities of parallel c-di-GMP signalling systems are segregated to avoid potentially deleterious cross-talk. Moreover, many 'hybrid' proteins contain both GGDEF and EAL domains; the relationship between the two apparently opposing enzymatic activities has been termed a 'biochemical conundrum'. Here, we present a computational analysis of 11 248 GGDEF- and EAL-containing proteins in 867 prokaryotic genomes to address these two outstanding questions. Over half of these proteins contain a signal for cell-surface localization, and a majority accommodate a signal-sensing partner domain; these indicate widespread prevalence of post-translational regulation that may segregate the activities of proteins that are co-expressed. By examining the conservation of amino acid residues in the GGDEF and EAL catalytic sites, we show that there are predominantly two types of hybrid proteins. In the first, both sites are intact; an additional regulatory partner domain, present in most of these proteins, might determine the balance between the two enzymatic activities. In the second type, only the EAL catalytic site is intact; these--unlike EAL-only proteins--generally contain a signal-sensing partner domain, suggesting distinct modes of regulation for EAL activity under different sequence contexts. Finally, we discuss the role of proteins that have lost GGDEF and EAL catalytic sites as potential c-di-GMP-binding effectors. Our findings will serve as a genomic framework for interpreting ongoing molecular investigations of these proteins.
authors.affiliation: EMBL-European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK. aswin@ebi.ac.uk
authors.forename: Aswin S N
authors.initials: AS
authors.lastname: Seshasayee
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Fraser
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Luscombe
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001419:Bacteria / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D020134:Catalytic Domain; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D020745:Genome, Archaeal; D016680:Genome, Bacterial; D023281:Genomics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019761:Phosphorus-Oxygen Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D015290:Second Messenger Systems
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C062025:bis(3',5')-cyclic diguanylic acid; D010727:Phosphoric Diester Hydrolases; D019761:Phosphorus-Oxygen Lyases; C060720:diguanylate cyclase; D006152:Cyclic GMP