Bullock T

References (2)

Title : Refined atomic model of wheat serine carboxypeptidase II at 2.2-A resolution - Liao_1992_Biochemistry_31_9796
Author(s) : Liao DI , Breddam K , Sweet RM , Bullock T , Remington SJ
Ref : Biochemistry , 31 :9796 , 1992
Abstract : The crystal structure of the homodimeric serine carboxypeptidase II from wheat (CPDW-II, M(r) 120K) has been determined and fully refined at 2.2-A resolution to a standard crystallographic R factor of 16.9% using synchrotron data collected at the Brookhaven National Laboratory. The model has an rms deviation from ideal bond lengths of 0.018 A and from bond angles of 2.8 degrees. The model supports the general conclusions of an earlier study at 3.5-A resolution and will form the basis for investigation into substrate binding and mechanistic studies. The enzyme has an alpha + beta fold, consisting of a central 11-stranded beta-sheet with a total of 15 helices on either side. The enzyme, like other serine proteinases, contains a "catalytic triad" Ser146-His397-Asp338 and a presumed "oxyanion hole" consisting of the backbone amides of Tyr147 and Gly53. The carboxylate of Asp338 and imidazole of His397 are not coplanar in contrast to the other serine proteinases. A comparison of the active site features of the three families of serine proteinases suggests that the "catalytic triad" should actually be regarded as two diads, a His-Asp diad and a His-Ser diad, and that the relative orientation of one diad with respect to the other is not particularly important. Four active site residues (52, 53, 65, and 146) have unfavorable backbone conformations but have well-defined electron density, suggesting that there is some strain in the active site region. The binding of the free amino acid arginine has been analyzed by difference Fourier methods, locating the binding site for the C-terminal carboxylate of the leaving group. The carboxylate makes hydrogen bonds to Glu145, Asn51, and the amide of Gly52. The carboxylate of Glu145 also makes a hydrogen bond with that of Glu65, suggesting that one or both may be protonated. Thus, the loss of peptidase activity at pH > 7 may in part be due to deprotonation of Glu145. The active site does not reveal exposed peptide amides and carbonyl oxygen atoms that could interact with substrate in an extended beta-sheet fashion. The fold of the polypeptide backbone is completely different than that of trypsin or subtilisin, suggesting that this is a third example of convergent molecular evolution to a common enzymatic activity. Furthermore, it is suggested that the active site sequence motif "G-X-S-X-G/A", often considered the hallmark of serine peptidase or esterase activity, is fortuitous and not the result of divergent evolution.
ESTHER : Liao_1992_Biochemistry_31_9796
PubMedSearch : Liao_1992_Biochemistry_31_9796
PubMedID: 1390755
Gene_locus related to this paper: wheat-cbp02

Title : Crystallization of serine carboxypeptidases - Wilson_1990_J.Mol.Biol_211_301
Author(s) : Wilson KP , Liao DI , Bullock T , Remington SJ , Breddam K
Ref : Journal of Molecular Biology , 211 :301 , 1990
Abstract : Crystallization of three different serine carboxypeptidases has been achieved by the method of hanging-drop vapor diffusion. Serine carboxypeptidases II from wheat bran and malted barley crystallize isomorphously from polyethylene glycol solutions at room temperature (pH 4 to 7) in space group P4(1)2(1)2 or enantiomorph with cell dimensions of a = b = 98.2 A and c = 209.5 A. The crystals diffract to about 2.3 A resolution using rotating-anode X-ray generators. Assuming a dimer of Mr 120,000 in the asymmetric unit, Vm = 2.1 A3/dalton. These crystals appear suitable for structural studies. A genetically engineered serine carboxypeptidase from yeast, which lacks three of four glycosylation sites present in the wild-type, has also been crystallized by vapor diffusion against methylpentanediol at 4 degrees C, pH 6.4 to 8.0.
ESTHER : Wilson_1990_J.Mol.Biol_211_301
PubMedSearch : Wilson_1990_J.Mol.Biol_211_301
PubMedID: 2308160
Gene_locus related to this paper: wheat-cbp02