Words similar to cyclases
Example sentences for: cyclases
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They are likely to function as sensors of diffusible gaseous ligands that activate at least three distinct, downstream signaling pathways: namely phosphotransfer through the two-component systems, methyl ester-dependent chemotactic response and cyclic nucleotide signaling through the diguanylate cyclases/phosphodiesterases.
The classical adenylyl cyclases, guanylyl cyclases and the GGDEF (diguanylate cyclase) domains share the catalytic palm domain with the family B DNA polymerases, reverse transcriptases, viral RNA dependent RNA polymerases and eukaryote-type primases [ 4 13 14 ] . The pathogenic adenylyl cyclases of several bacteria and the CyaA-like proteobacteria adenylyl cyclases are extremely divergent versions of the catalytic domain seen in the Pol-β family of nucleotidyl transferases [ 15 ] (also see SCOP database: http://scop.mrc-lmb.cam.ac.uk/scop/).
The RDRPs of RNA viruses define one major lineage of nucleic acid polymerases, which additionally includes reverse transcriptases, archaeo-eukaryotic DNA polymerases, and nucleotide cyclases [ 8 9 10 11 12 13 ] . The DNA-dependent RNA polymerase of certain bacteriophages, such as T7, and the archaeo-eukaryotic primase (also detected in some bacteria) are divergent derivatives of the same fold [ 11 14 ] . The core catalytic domain of all these enzymes, the so-called "palm" domain, has an RNA-recognition motif (RRM)-like fold with strategically placed metal-coordinating residues, which form the active site [ 11 15 16 ] . In contrast, bacterial DnaG-type primases (also present in archaea and some eukaryotes) contain a polymerase domain of the Rossmann-like TOPRIM fold, which is shared with topoisomerases and OLD-family nucleases [ 17 18 19 ] . The recently solved structures of the DDRPs from yeast and the thermophilic bacterium Thermus thermophilus indicate that the β' subunit (according to the subunit nomenclature of Escherichia coli DDRP, which we hereinafter employ to designate all orthologs of the respective E. coli subunits) of these enzymes defines another distinct catalytic scaffold, which is unrelated to any of the above template-dependent RNA polymerases [ 20 21 22 23 24 ] . Additionally, the structural and evolutionary affinities of two other template-dependent RNA polymerases, namely RDRPs involved in PTGS [ 25 26 27 ] and primases of herpesviruses [ 28 ] , remain obscure.
The majority of previously known nucleotide cyclases belong to two major folds.
Organic phosphate compounds are the central metabolites of all biological systems [ 1 2 ] . Some are the basic building blocks of nucleic acids, some like ATP and GTP, are additionally, cellular energy stores, others like cAMP or cGMP are messengers in signal transduction, and, yet others, such as FAD, NAD, thiamine phosphates and pyridoxal phosphate are cofactors for a range of enzymes [ 1 2 ] . Protein domains belonging to a relatively small set of structural folds are known to bind or catalyze reactions that utilize these organic phosphate compounds (see SCOP database: http://scop.mrc-lmb.cam.ac.uk/scop/) [ 3 4 ] . Several of these folds trace back to some of the earliest phases of the evolution of the protein world, and participate in a wide range of disparate biological functions in extant proteins [ 4 5 ] . Some folds, such as the P-loop fold, the Rossmann fold and the Hsp70-like fold, have been well studied, and comprise mainly of dedicated nucleotide binding or hydrolyzing proteins [ 6 7 8 9 ] . Others, such as the palm-domain, which is found in adenylyl cyclases and various nucleic acid polymerases, belong to more generalized protein folds that contain representatives with diverse biochemical activities [ 4 10 11 ] . Current availability of extensive genome sequence data, allows one to identify less numerous, nevertheless biological important organic phosphate-binding domains that may have previous eluded detection.
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