Biomedical subjects

A A Antson

Publications and source records attributed to A A Antson.

9 recordsLinked to original sources

PubMed1997

The crystal structure of Citrobacter freundii tyrosine phenol-lyase complexed with 3-(4'-hydroxyphenyl)propionic acid, together with site-directed mutagenesis and kinetic analysis, demonstrates that arginine 381 is required for substrate specificity.

The X-ray structure of tyrosine phenol-lyase (TPL) complexed with a substrate analog, 3-(4'-hydroxyphenyl)propionic acid, shows that Arg 381 is located in the substrate binding site, with the side-chain NH1 4.1 A from the 4'-OH of the analog. The structure has been deduced at 2.5 A resolution using crystals that belong to the P2(1)2(1)2 space group with a = 135.07 A, b = 143.91 A, and c = 59.80 A. To evaluate the role of Arg 381 in TPL catalysis, we prepared mutant proteins replacing arginine with alanine (R381A), with isoleucine (R381I), and with valine (R381V). The beta-elimination activity of R381A TPL has been reduced by 10(-4)-fold compared to wild type, whereas R381I and R381V TPL exhibit no detectable beta-elimination activity with L-tyrosine as substrate. However, R381A, R381I, and R381V TPL react with S-(o-nitrophenyl)-L-cysteine, beta-chloro-L-alanine, O-benzoyl-L-serine, and S-methyl-L-cysteine and exhibit k(cat) and k(cat)/Km values comparable to those of wild-type TPL. Furthermore, the Ki values for competitive inhibition by L-tryptophan and L-phenylalanine are similar for wild-type, R381A, and R381I TPL. Rapid-scanning-stopped flow spectroscopic analyses also show that wild-type and mutant proteins can bind L-tyrosine and form quinonoid complexes with similar rate constants. The binding of 3-(4'-hydroxyphenyl)propionic acid to wild-type TPL decreases at high pH values with a pKa of 8.4 and is thus dependent on an acidic group, possibly Arg404, which forms an ion pair with the analog carboxylate, or the pyridoxal 5'-phosphate Schiff base. R381A TPL shows only a small decrease in k(cat)/Km for tyrosine at lower pH, in contrast to wild-type TPL, which shows two basic pKas with an average value of about 7.8. Thus, it is possible that Arg 381 is one of the catalytic bases previously observed in the pH dependence of k(cat)/Km of TPL with L-tyrosine [Kiick, D. M., & Phillips. R. S. (1988) Biochemistry 27, 7333-7338], and hence Arg 381 is at least partially responsible for the substrate specificity of TPL.

Arginine↗

PubMed1997

RNA cleavage without hydrolysis. Splitting the catalytic activities of binase with Asn101 and Thr101 mutations.

Members of the microbial guanyl-specific ribonuclease family catalyse the endonucleolytic cleavage of single-stranded RNA in a two-step reaction involving transesterification to form a 2',3'-cyclic phosphate and its subsequent hydrolysis to yield the respective 3'-phosphate. The extracellular ribonuclease from Bacillus intermedius (binase, RNase Bi) shares a common mechanism for RNA hydrolysis with mammalian RNases. Two catalytic residues in the active site of binase, Glu72 and His101, are thought to be involved in general acid-general base catalysis of RNA cleavage. Using site-directed mutagenesis, binase mutants were produced containing amino acid substitutions H101N and H101T and their catalytic properties towards RNA, poly(I), poly(A), GpC and guanosine 2',3'-cyclic phosphate (cGMP) substrates were studied. The engineered mutant proteins are active in the transesterification step which produces the 2',3'-cyclic phosphate species but they have lost the ability to catalyse hydrolysis of the cyclic phosphate to give the 3' monophosphate product.

Asparagine↗

PubMed1996

Circular assemblies.

During 1994 and 1995, the structures of the serum amyloid P component, the bacterial chaperonin GroEL, the 20S proteasome, the bacterial light-harvesting complexes and the tryptophan operon RNA-binding attenuation protein have been determined. These structures all form circular assemblies in which the individual subunits are related by rotational symmetry. In most cases the circular organization generates a new biophysical property and a specific biological function which have presumably been selected by evolution.

Bacterial Proteins↗

PubMed1995

The structure of trp RNA-binding attenuation protein.

The crystal structure of the trp RNA-binding attenuation protein of Bacclius subtilis solved at 1.8 A resolution reveals a novel structural arrangement in which the eleven subunits are stabilized through eleven intersubunit beta-sheets to form a beta-wheel with a large central hole. The nature of the binding of L-tryptophan in clefts between adjacent beta-sheets in the beta-wheel suggests that this binding induces conformational changes in the flexible residues 25-33 and 49-52. It is argued that upon binding, the messenger RNA target forms a matching circle in which eleven U/GAG repeats are bound to the surface of the protein ondecamer modified by the binding of L-tryptophan.

Amino Acid Sequence↗

PubMed1994

11-fold symmetry of the trp RNA-binding attenuation protein (TRAP) from Bacillus subtilis determined by X-ray analysis.

The trp RNA-binding attenuation protein (TRAP) of Bacillus subtilis has been crystallized and examined by crystallography using X-ray synchrotron radiation diffraction data. Crystals of TRAP complexed with L-tryptophan belong to space group C2 with a = 156.8 A, b = 114.05 A, c = 105.9 A, beta = 118.2 degrees. Crystals of a potential heavy-atom derivative of TRAP complexed with 5-bromo-L-tryptophan grow in the same space group with similar cell dimensions. X-ray data for the native crystals and for the derivative have been collected to 2.9 A and 2.2 A resolution, respectively. Peaks in the self-rotation function and in the Patterson synthesis could only be explained by two 11-subunit oligomers (each formed by an 11-fold axis of symmetry) in the asymmetric unit lying with the 11-fold rotation axes parallel to each other. The consequence is that the TRAP molecule has 11-fold symmetry and contains 11 subunits.

Bacillus subtilis↗

PubMed1994

Crystallization and preliminary X-ray investigation of holotryptophanases from Escherichia coli and Proteus vulgaris.

Crystals of Proteus vulgaris holotryptophanase have been grown by the hanging-drop technique using polyethylene glycol 4000 as precipitant in the presence of monovalent cations K+ or Cs+. Orthorhombic crystals (P2(1)2(1)2(1)) grown with Cs+ have unit cell parameters a = 115.0 A, b = 118.2 A and c = 153.7 A and diffract to 1.8 A. There are four subunits of the tetrameric molecule in the asymmetric unit. Native data have been collected to 2.5 A resolution. The 3.4 A data were collected from tetragonal crystals of Escherichia coli holotryptophanase grown under conditions described by Kawata et al. (1991). The molecular replacement solution for this crystal form has been found using tyrosine phenol-lyase coordinates. The correct enantiomorph is P4(3)2(1)2. There are two subunits in the asymmetric unit.

Crystallization↗

PubMed1993

Three-dimensional structure of tyrosine phenol-lyase.

Tyrosine phenol-lyase (EC 4.1.99.2) from Citrobacter freundii has been cloned and the primary sequence deduced from the DNA sequence. From the BrCN digest of the NaBH4-reduced holoenzyme, five peptides were purified and sequenced. The amino acid sequences of the peptides agreed with the corresponding parts of the tyrosine phenol-lyase sequence obtained from the gene structure. K257 is the pyridoxal 5'-phosphate binding residue. Assisted by the sequence data, the crystal structure of apotyrosine phenol-lyase, a pyridoxal 5'-phosphate-dependent enzyme, has been refined to an R-factor of 16.2% at 2.3-A resolution using synchrotron radiation diffraction data. The tetrameric molecule has 222 symmetry, with one of the axes coincident with the crystallographic 2-fold symmetry axis of the crystal which belongs to the space group P2(1)2(1)2 with a = 76.0 A, b = 138.3 A, and c = 93.5 A. Each subunit comprises 14 alpha-helices and 16 beta-strands, which fold into a small and a large domain. The coenzyme-binding lysine residue is located at the interface between the large and small domains of one subunit and the large domain of a crystallographically related subunit. The fold of the large, pyridoxal 5'-phosphate binding domain and the location of the active site are similar to that found in aminotransferases. Most of the residues which participate in binding of pyridoxal 5'-phosphate in aminotransferases are conserved in the structure of tyrosine phenol-lyase. Two dimers of tyrosine phenol-lyase, each of which has a domain architecture similar to that found in aspartate aminotransferases, are bound together through a hydrophobic cluster in the center of the molecule and intertwined N-terminal arms.

Amino Acid Sequence↗

PubMed1992

The polypeptide chain fold in tyrosine phenol-lyase, a pyridoxal-5'-phosphate-dependent enzyme.

The tyrosine phenol lyase (EC 4.1.99.2) from Citrobacter intermedius has been crystallised in the apo form by vapour diffusion. The space group is P2(1)2(1)2. The unit cell has dimensions a = 76.0 A, b = 138.3 A, c = 93.5 A and it contains two subunits of the tetrameric molecule in the asymmetric unit. Diffraction data for the native enzyme and two heavy atom derivatives have been collected with synchrotron radiation and an image plate scanner. The structure has been solved at 2.7 A resolution by isomorphous replacement with subsequent modification of the phases by averaging the density around the non-crystallographic symmetry axis. The electron density maps clearly show the relative orientation of the subunits and most of the trace of the polypeptide chain. Each subunit consists of two domains. The topology of the large domain appears to be similar to that of the aminotransferases.

Chemical Phenomena↗

PubMed1988

Crystallization and crystal data on tyrosine phenol-lyase.

Crystals of the apoenzyme of tyrosine phenol-lyase (EC 4.1.99.2), a pyridoxal 5'-phosphate-dependent enzyme from Citrobacter intermedius, have been grown by vapor diffusion of an ammonium sulfate solution to a protein solution. The crystals belong to space group P2(1)2(1)2, with dimensions of a = 75.5 A, b = 138.4 A and c = 94.1 A and diffract up to 2.7 A resolution. The asymmetric unit contains one half of the enzyme tetrameric molecule. Two heavy-atom derivatives of the crystals have been obtained.

Ammonium Sulfate↗