Crystal structure of a concentrative nucleoside transporter from Vibrio cholerae at 2.4 Å.

Nucleosides are required for DNA and RNA synthesis, and the nucleoside adenosine has a function in a variety of signalling processes. Transport of nucleosides across cell membranes provides the major source of nucleosides in many cell types and is also responsible for the termination of adenosine signalling. As a result of their hydrophilic nature, nucleosides require a specialized class of integral membrane proteins, known as nucleoside transporters (NTs), for specific transport across cell membranes.

Engineering splicing factors with designed specificities.

Alternative splicing is generally regulated by trans-acting factors that specifically bind pre-mRNA to activate or inhibit the splicing reaction. This regulation is critical for normal gene expression, and dysregulation of splicing is closely associated with human diseases. Here we engineered artificial splicing factors by combining sequence-specific RNA-binding domains of human Pumilio1 with functional domains that regulate splicing.

Engineering RNA sequence specificity of Pumilio repeats.

Puf proteins bind RNA sequence specifically and regulate translation and stability of target mRNAs. A "code" for RNA recognition has been deduced from crystal structures of the Puf protein, human Pumilio1, where each of eight repeats binds an RNA base via a combination of three side chains at conserved positions. Here, we report the creation of seven soluble mutant proteins with predictably altered sequence specificity, including one that binds tightly to adenosine-uracil-rich element RNA.

Crystal structures of human bifunctional enzyme aminoimidazole-4-carboxamide ribonucleotide transformylase/IMP cyclohydrolase in complex with potent sulfonyl-containing antifolates.

Aminoimidazole-4-carboxamide ribonucleotide (AICAR) transformylase/IMP cyclohydrolase (ATIC) is a bifunctional enzyme with folate-dependent AICAR transformylase and IMP cyclohydrolase activities that catalyzes the last two steps of purine biosynthesis. The AICAR transformylase inhibitors BW1540 and BW2315 are sulfamido-bridged 5,8-dideazafolate analogs with remarkably potent K(i) values of 8 and 6 nm, respectively, compared with most other antifolates. Crystal structures of ATIC at 2.

Structural insights into the human and avian IMP cyclohydrolase mechanism via crystal structures with the bound XMP inhibitor.

Within de novo purine biosynthesis, the AICAR transformylase and IMP cyclohydrolase activities of the bifunctional enzyme ATIC convert the intermediate AICAR to the final product of the pathway, IMP. Identification of the AICAR transformylase active site and a proposed formyl transfer mechanism have already resulted from analysis of crystal structures of avian ATIC in complex with substrate and/or inhibitors. Herein, we focus on the IMPCH active site and the cyclohydrolase mechanism through comparison of crystal structures of XMP inhibitor complexes of human ATIC at 1.

Structural studies of the L-threonine-O-3-phosphate decarboxylase (CobD) enzyme from Salmonella enterica: the apo, substrate, and product-aldimine complexes.

The evolution of biosynthetic pathways is difficult to reconstruct in hindsight; however, the structures of the enzymes that are involved may provide insight into their development. One enzyme in the cobalamin biosynthetic pathway that appears to have evolved from a protein with different function is L-threonine-O-3-phosphate decarboxylase (CobD) from Salmonella enterica, which is structurally similar to histidinol phosphate aminotransferase [Cheong, C. G.

Capture of a labile substrate by expulsion of water molecules from the active site of nicotinate mononucleotide:5,6-dimethylbenzimidazole phosphoribosyltransferase (CobT) from Salmonella enterica.

Nicotinate mononucleotide (NaMN):5,6-dimethylbenzimidazole (DMB) phosphoribosyltransferase (CobT) from Salmonella enterica plays a central role in the synthesis of alpha-ribazole-5'-phosphate, an intermediate for the lower ligand of cobalamin. In earlier studies it proved difficult to obtain the structure of CobT bound to NaMN because it is hydrolyzed in the crystal lattice in the absence of the second substrate DMB. In an effort to map the reaction pathway of this enzyme, NaMN was captured in the active site with the substrate analogs 4,5-dimethyl-1,2-phenylenediamine, 4-methylcatechol, indole, 3,4-dimethylaniline, 2,5-dimethylaniline, 3,4-dimethylphenol, and 2-amino-p-cresol.

Three-dimensional structure of the L-threonine-O-3-phosphate decarboxylase (CobD) enzyme from Salmonella enterica.

The three-dimensional structure of the pyridoxal 5'-phosphate (PLP)-dependent L-threonine-O-3-phosphate decarboxylase (CobD) from Salmonella enterica is described here. This enzyme is responsible for synthesizing (R)-1-amino-2-propanol phosphate which is the precursor for the linkage between the nucleotide loop and the corrin ring in cobalamin. The molecule is a molecular dimer where each subunit consists of a large and small domain.