title: The complex between ribonuclease T1 and 3'GMP suggests geometry of enzymic reaction path. An X-ray study.
abstract: The crystal structure of the complex between ribonuclease T1 and 3'GMP suggests that (a) a substrate GpN is bound to the active site of ribonuclease T1 in a conformation that actively supports the catalytic process, (b) the reaction occurs in an in-line process, (c) His40 N epsilon H+ activates O2'-H, (d) Glu58 carboxylate acts as base and His92 N epsilon H+ as acid in a general acid-base catalysis. The crystals have the monoclinic space group P2(1), a = 4.968 nm, b = 4.833 nm, c = 4.048 nm, beta = 90.62 degrees with two molecules in the asymmetric unit. The structure was determined by molecular replacement and refined to R = 15.3% with 11,338 data > or = 1 sigma (Fo) in the resolution range 1.0-0.2 nm; this includes 180 water molecules and two Ca2+. The structure of ribonuclease T1 is as previously observed. 3'GMP is bound in syn conformation; guanine is located in the specific recognition site, the ribose adopts C4'-exo puckering, the ribose phosphate is extended with torsion angle epsilon in trans. The O2'-H group is activated by accepting and donating hydrogen bonds from His40 N epsilon H+ and to Glu58 O epsilon 1; the phosphate is hydrogen bonded to Glu58 O epsilon 2H, Arg77 N epsilon H+ and N eta 2H+, Tyr38 O eta H, His92 N eta H+. The conformation of ribose phosphate is such that O2' is at a distance of 0.31 nm from phosphorus, and opposite the P-OP3 bond which accepts a hydrogen bond from His92 N epsilon H+; we infer from a model building study that this bond is equivalent to the scissile P-O5' in a substrate GpN.
authors.affiliation: Institut für Kristallographie, Freie Universität Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Heydenreich
authors.forename: G
authors.initials: G
authors.lastname: Koellner
authors.forename: H W
authors.initials: HW
authors.lastname: Choe
authors.forename: F
authors.initials: F
authors.lastname: Cordes
authors.forename: C
authors.initials: C
authors.lastname: Kisker
authors.forename: H
authors.initials: H
authors.lastname: Schindelin
authors.forename: R
authors.initials: R
authors.lastname: Adamiak
authors.forename: U
authors.initials: U
authors.lastname: Hahn
authors.forename: W
authors.initials: W
authors.lastname: Saenger
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D006147:Guanine / Q000737:chemistry*; D006157:Guanosine Monophosphate / Q000737:chemistry / Q000378:metabolism*; D006860:Hydrogen Bonding; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D006163:Ribonuclease T1 / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D006147:Guanine; C068152:3'-guanylic acid; D006157:Guanosine Monophosphate; D006163:Ribonuclease T1; D002118:Calcium