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Excitement in protein science comes from unexpected structural findings that shed new light on functional mechanisms. Just such a series of insights is now beginning to emerge from two recently published structures of the scaffolding protein PSD-95.
Phosphorylase kinase (PhK) integrates hormonal and neuronal signals and is a key enzyme in the control of glycogen metabolism. PhK is one of the largest of the protein kinases and is composed of four types of subunit, with stoichiometry (αβγδ) 4 and a total MW of 1.3 x 10 6 . PhK catalyzes the phosphorylation of inactive glycogen phosphorylase b (GPb), resulting in the formation of...
dTDP-D-glucose 4,6-dehydratase (RmlB) was first identified in the L-rhamnose biosynthetic pathway, where it catalyzes the conversion of dTDP-D-glucose into dTDP-4-keto-6-deoxy-D-glucose. The structures of RmlB from Salmonella enterica serovar Typhimurium in complex with substrate deoxythymidine 5'-diphospho-D-glucose (dTDP-D-glucose) and deoxythymidine 5'-diphosphate (dTDP), and RmlB from Streptococcus...
Transforming growth factor β (TGF-β) is a secreted growth factor that regulates the transcriptional program of cells via heteromeric complexes of transmembrane type II and type I Ser/Thr kinase receptors and the Smad intracellular signal transduction pathway . The activity of this pathway is tightly controlled by serine phosphorylation, which plays a key role in regulating protein-protein interactions...
Methylaspartate ammonia lyase (MAL) catalyzes the magnesium-dependent reversible α,β-elimination of ammonia from L-threo-(2S,3S)-3-methylaspartic acid to mesaconic acid. The 1.3 A MAD crystal structure of the dimeric Citrobacter amalonaticus MAL shows that each subunit comprises two domains, one of which adopts the classical TIM barrel fold, with the active site at the C-terminal end of the barrel...
Flavonoids are common colorants in plants and have long-established biomedicinal properties. Anthocyanidin synthase (ANS), a 2-oxoglutarate iron-dependent oxygenase, catalyzes the penultimate step in the biosynthesis of the anthocyanin class of flavonoids. The crystal structure of ANS reveals a multicomponent active site containing metal, cosubstrate, and two molecules of a substrate analog (dihydroquercetin)...
Histidine ammonia-lyase requires a 4-methylidene-imidazole-5-one group (MIO) that is produced autocatalytically by a cyclization and dehydration step in a 3-residue loop of the polypeptide. The crystal structures of three mutants have been established. Two mutants were inactive and failed to form MIO, but remained unchanged elsewhere. The third mutant showed very low activity and formed MIO, although...
Although the eukaryotic (eRF1) and prokaryotic (RF2) polypeptide release (translation termination) factors are functionally similar, they turn out to be very different in overall shape and architecture and in the location of key functional elements.
Interphotoreceptor retinoid binding protein (IRBP), the major soluble component of the interphotoreceptor matrix, is critical to the function, integrity, and development of the vertebrate retina. Although its role is poorly understood, IRBP has been thought to protect 11-cis retinal and all-trans retinol while facilitating their exchange between the photoreceptors and retinal-pigmented epithelium...
Protein partnerships provide specificity for transcription factors that display conserved DNA binding properties. The newest Ets-1 partner Pax-5 directs a surprising conformational change that maximizes the protein interface and changes binding site preference.
Pressures in the 100 MPa range are known to have an enormous number of effects on the action of proteins, but straightforward means for determining the structural basis of these effects have been lacking. Here, crystallography has been used to probe effects of pressure on sperm whale myoglobin structure. A comparison of pressure effects with those seen at low pH suggests that structural changes under...
Nicotinamide/Nicotinate mononucleotide (NMN/NaMN) adenylyltransferase is an indispensable enzyme in both de novo biosynthesis and salvage of NAD + and NADP + . In prokaryotes, it is absolutely required for cell survival, thus representing an attractive target for the development of new broad-spectrum antibacteria inhibitors. The crystal structures of E. coli NaMN adenylyltransferase...
Xanthine dehydrogenase (XDH), a complex molybdo/iron-sulfur/flavoprotein, catalyzes the oxidation of hypoxanthine to xanthine followed by oxidation of xanthine to uric acid with concomitant reduction of NAD + . The 2.7 A resolution structure of Rhodobacter capsulatus XDH reveals that the bacterial and bovine XDH have highly similar folds despite differences in subunit composition. The NAD...
Phosphorylase kinase (PhK), a Ca 2+ -dependent regulatory enzyme of the glycogenolytic cascade in skeletal muscle, is a 1.3 MDa hexadecameric oligomer comprising four copies of four distinct subunits, termed α, β, γ, and δ, the last being endogenous calmodulin. The structures of both nonactivated and Ca 2+ -activated PhK were determined to elucidate Ca 2+ -induced...
The crystal structure of the hypothetical protein MJ1247 from Methanococccus jannaschii at 2 A resolution, a detailed sequence analysis, and biochemical assays infer its molecular function to be 3-hexulose-6-phosphate isomerase (PHI). In the dissimilatory ribulose monophosphate (RuMP) cycle, ribulose-5-phosphate is coupled to formaldehyde by the 3-hexulose-6-phosphate synthase (HPS), yielding hexulose-6-phosphate,...
Since reactive ammonia is not available under physiological conditions, glutamine is used as a source for the incorporation of nitrogen in a number of metabolic pathway intermediates. The heterodimeric ImGP synthase that links histidine and purine biosynthesis belongs to the family of glutamine amidotransferases in which the glutaminase activity is coupled with a subsequent synthase activity specific...
Calponin is involved in the regulation of contractility and organization of the actin cytoskeleton in smooth muscle cells. It is the archetypal member of the calponin homology (CH) domain family of actin binding proteins that includes cytoskeletal linkers such as α-actinin, spectrin, and dystrophin, and regulatory proteins including VAV, IQGAP, and calponin. We have determined the first structure...
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