title: Structures of the γ-class carbonic anhydrase homologue YrdA suggest a possible allosteric switch.
abstract: The YrdA protein shows high sequence similarity to γ-class carbonic anhydrase (γ-CA) proteins and is classified as part of the γ-CA protein family. However, its function has not been fully elucidated as it lacks several of the conserved residues that are considered to be necessary for γ-CA catalysis. Interestingly, a homologue of γ-CA from Methanosarcina thermophila and a β-carboxysomal γ-CA from a β-cyanobacterium have shown that these catalytic residues are not always conserved in γ-CAs. The crystal structure of YrdA from Escherichia coli (ecYrdA) is reported here in two crystallographic forms. The overall structure of ecYrdA is also similar to those of the γ-CAs. One loop around the putative catalytic site shows a number of alternative conformations. A His residue (His70) on this loop coordinates with, or is reoriented from, the catalytic Zn(2+) ion; this is similar to the conformations mediated by an Asp residue on the catalytic loops of β-CA proteins. One Trp residue (Trp171) also adopts two alternative conformations that may be related to the spatial positions of the catalytic loop. Even though significant CA activity could not be detected using purified ecYrdA, these structural features have potential functional implications for γ-CA-related proteins.
authors.affiliation: Department of Chemistry and Institute of Basic Sciences, Chonnam National University, 300 Yongbong-dong, Buk-gu, Gwangju 500-757, Republic of Korea.
authors.forename: Hye-Mi
authors.initials: HM
authors.lastname: Park
authors.forename: Jeong-Hoh
authors.initials: JH
authors.lastname: Park
authors.forename: Ji-Woo
authors.initials: JW
authors.lastname: Choi
authors.forename: Jieun
authors.initials: J
authors.lastname: Lee
authors.forename: Bo Yeon
authors.initials: BY
authors.lastname: Kim
authors.forename: Che-Hun
authors.initials: CH
authors.lastname: Jung
authors.forename: Jeong-Sun
authors.initials: JS
authors.lastname: Kim
mesh_terms: D000495:Allosteric Site; D000595:Amino Acid Sequence; D002256:Carbonic Anhydrases / Q000737:chemistry*; D020134:Catalytic Domain; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D007477:Ions; D007501:Iron / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D014364:Tryptophan / Q000737:chemistry; D015032:Zinc / Q000737:chemistry
chemical_list: D029968:Escherichia coli Proteins; D007477:Ions; D006639:Histidine; D014364:Tryptophan; D007501:Iron; D002256:Carbonic Anhydrases; D015032:Zinc