Biochemical discrimination between selenium and sulfur 1: a single residue provides selenium specificity to human selenocysteine lyase.

Selenium and sulfur are two closely related basic elements utilized in nature for a vast array of biochemical reactions. While toxic at higher concentrations, selenium is an essential trace element incorporated into selenoproteins as selenocysteine (Sec), the selenium analogue of cysteine (Cys). Sec lyases (SCLs) and Cys desulfurases (CDs) catalyze the removal of selenium or sulfur from Sec or Cys and generally act on both substrates.

Biochemical discrimination between selenium and sulfur 2: mechanistic investigation of the selenium specificity of human selenocysteine lyase.

Selenium is an essential trace element incorporated into selenoproteins as selenocysteine. Selenocysteine (Sec) lyases (SCLs) and cysteine (Cys) desulfurases (CDs) catalyze the removal of selenium or sulfur from Sec or Cys, respectively, and generally accept both substrates. Intriguingly, human SCL (hSCL) is specific for Sec even though the only difference between Sec and Cys is a single chalcogen atom.

Crystal structure of human RNA helicase A (DHX9): structural basis for unselective nucleotide base binding in a DEAD-box variant protein.

RNA helicases of the DExD/H-box superfamily are critically involved in all RNA-related processes. No crystal structures of human DExH-box domains had been determined previously, and their structures were difficult to predict owing to the low level of homology among DExH-motif-containing proteins from diverse species. Here we present the crystal structures of the conserved domain 1 of the DEIH-motif-containing helicase DHX9 and of the DEAD-box helicase DDX20.

Structural basis for inhibitor specificity in human poly(ADP-ribose) polymerase-3.

Poly(ADP-ribose) polymerases (PARPs) activate DNA repair mechanisms upon stress- and cytotoxin-induced DNA damage, and inhibition of PARP activity is a lead in cancer drug therapy. We present a structural and functional analysis of the PARP domain of human PARP-3 in complex with several inhibitors. Of these, KU0058948 is the strongest inhibitor of PARP-3 activity.

The DEXD/H-box RNA helicase DDX19 is regulated by an {alpha}-helical switch.

DEXD/H-box RNA helicases couple ATP hydrolysis to RNA remodeling by an unknown mechanism. We used x-ray crystallography and biochemical analysis of the human DEXD/H-box protein DDX19 to investigate its regulatory mechanism. The crystal structures of DDX19, in its RNA-bound prehydrolysis and free posthydrolysis state, reveal an alpha-helix that inserts between the conserved domains of the free protein to negatively regulate ATPase activity.

Structural basis for the inhibition mechanism of human cystathionine gamma-lyase, an enzyme responsible for the production of H(2)S.

Impairment of the formation or action of hydrogen sulfide (H(2)S), an endogenous gasotransmitter, is associated with various diseases, such as hypertension, diabetes mellitus, septic and hemorrhagic shock, and pancreatitis. Cystathionine beta-synthase and cystathionine gamma-lyase (CSE) are two pyridoxal-5'-phosphate (PLP)-dependent enzymes largely responsible for the production of H(2)S in mammals. Inhibition of CSE by DL-propargylglycine (PAG) has been shown to alleviate disease symptoms.

Zinc binding catalytic domain of human tankyrase 1.

Tankyrases are recently discovered proteins implicated in many important functions in the cell including telomere homeostasis and mitosis. Tankyrase modulates the activity of target proteins through poly(ADP-ribosyl)ation, and here we report the structure of the catalytic poly(ADP-ribose) polymerase (PARP) domain of human tankyrase 1. This is the first structure of a PARP domain from the tankyrase subfamily.

Structure of human argininosuccinate synthetase.

Argininosuccinate synthetase catalyzes the transformation of citrulline and aspartate into argininosuccinate and pyrophosphate using the hydrolysis of ATP to AMP and pyrophosphate. This enzymatic process constitutes the rate-limiting step in both the urea and arginine-citrulline cycles. Previous studies have investigated the crystal structures of argininosuccinate synthetase from bacterial species.

Crystal structures of mammalian glutamine synthetases illustrate substrate-induced conformational changes and provide opportunities for drug and herbicide design.

Glutamine synthetase (GS) catalyzes the ligation of glutamate and ammonia to form glutamine, with concomitant hydrolysis of ATP. In mammals, the activity eliminates cytotoxic ammonia, at the same time converting neurotoxic glutamate to harmless glutamine; there are a number of links between changes in GS activity and neurodegenerative disorders, such as Alzheimer's disease. In plants, because of its importance in the assimilation and re-assimilation of ammonia, the enzyme is a target of some herbicides.

Crystal structure of conserved domains 1 and 2 of the human DEAD-box helicase DDX3X in complex with the mononucleotide AMP.

DExD-box helicases are involved in all aspects of cellular RNA metabolism. Conserved domains 1 and 2 contain nine signature motifs that are responsible for nucleotide binding, RNA binding and ATP hydrolysis. The human DEAD-box helicase DDX3X has been associated with several different cellular processes, such as cell-growth control, mRNA transport and translation, and is suggested to be essential for the export of unspliced/partially spliced HIV mRNAs from the nucleus to the cytoplasm.

Purification and characterization of Thermus thermophilus UvrD.

The DNA helicase UvrD (helicase II) protein plays an important role in nucleotide excision repair, mismatch repair, rolling circular plasmid replication, and in DNA replication. A homologue of the Escherichia coli uvrD gene was previously identified in Thermus thermophilus; however, to date, a UvrD helicase has not been purified and characterized from a thermophile. Here we report the purification and characterization of a UvrD protein from Thermus thermophilus HB8.

Characterization of an endonuclease IV 3'-5' exonuclease activity.

Previous characterization of Escherichia coli endonuclease IV has shown that the enzyme specifically cleaves the DNA backbone at apurinic/apyrimidinic sites and removes 3' DNA blocking groups. By contrast, and unlike the major apurinic/apyrimidinic endonuclease exonuclease III, negligible exonuclease activity has been associated with endonuclease IV. Here we report that endonuclease IV does possess an intrinsic 3'-5' exonuclease activity.