title: Structural parsimony in endonuclease active sites: should the number of homing endonuclease families be redefined?
abstract: Homing endonucleases are classified into four families based on active site sequence motifs. Through structural comparisons we have found structural similarities between the endonuclease domain of colicin E9, an H-N-H motif-containing enzyme, and both the non-specific nuclease from Serratia and I-PpoI, a His-Cys box-containing homing endonuclease. Our comparison identifies conservation at the heart of all three enzyme active sites and so argues for a re-classification of H-N-H and His-Cys box homing endonucleases as a single family. We suggest the 'betabetaalpha-Me family' of homing enzymes to reflect the three elements of secondary structure and the metal ion that define the motif.
authors.affiliation: School of Chemical Sciences, University of East Anglia, Norwich, UK.
authors.forename: U C
authors.initials: UC
authors.lastname: Kühlmann
authors.forename: G R
authors.initials: GR
authors.lastname: Moore
authors.forename: R
authors.initials: R
authors.lastname: James
authors.forename: C
authors.initials: C
authors.lastname: Kleanthous
authors.forename: A M
authors.initials: AM
authors.lastname: Hemmings
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification; D001665:Binding Sites; D003087:Colicins / Q000737:chemistry* / Q000235:genetics; D017124:Conserved Sequence; D004706:Endodeoxyribonucleases / Q000737:chemistry* / Q000235:genetics; D004720:Endonucleases / Q000737:chemistry* / Q000145:classification* / Q000235:genetics; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D003087:Colicins; D004706:Endodeoxyribonucleases; D004720:Endonucleases; C064579:I-Ppo endonuclease