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Secondary-structural Elements (secondary-structural + element)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Expansion of the aspartate ,-semialdehyde dehydrogenase family: the first structure of a fungal ortholog

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2010
Buenafe T. Arachea
The enzyme aspartate semialdehyde dehydrogenase (ASADH) catalyzes a critical transformation that produces the first branch-point intermediate in an essential microbial amino-acid biosynthetic pathway. The first structure of an ASADH isolated from a fungal species (Candida albicans) has been determined as a complex with its pyridine nucleotide cofactor. This enzyme is a functional dimer, with a similar overall fold and domain organization to the structurally characterized bacterial ASADHs. However, there are differences in the secondary-structural elements and in cofactor binding that are likely to cause the lower catalytic efficiency of this fungal enzyme. Alterations in the dimer interface, through deletion of a helical subdomain and replacement of amino acids that participate in a hydrogen-bonding network, interrupt the intersubunit-communication channels required to support an alternating-site catalytic mechanism. The detailed functional information derived from this new structure will allow an assessment of ASADH as a possible target for antifungal drug development. [source]

Structure of a Nudix protein from Pyrobaculum aerophilum reveals a dimer with two intersubunit ,-­sheets

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2002
Shuishu Wang
Nudix proteins, formerly called MutT homolog proteins, are a large family of proteins that play an important role in reducing the accumulation of potentially toxic compounds inside the cell. They hydrolyze a wide variety of substrates that are mainly composed of a nucleoside diphosphate linked to some other moiety X and thus are called Nudix hydrolases. Here, the crystal structure of a Nudix hydrolase from the hyperthermophilic archaeon Pyrobaculum aerophilum is reported. The structure was determined by the single-wavelength anomalous scattering method with data collected at the peak anomalous wavelength of an iridium-derivatized crystal. It reveals an extensive dimer interface, with each subunit contributing two strands to the ,-sheet of the other subunit. Individual subunits consist of a mixed highly twisted and curved ,-sheet of 11 ,-strands and two ,-helices, forming an ,,,,, sandwich. The conserved Nudix box signature motif, which contains the essential catalytic residues, is located at the first ,-helix and the ,-strand and loop preceding it. The unusually short connections between secondary-structural elements, together with the dimer form of the structure, are likely to contribute to the thermostability of the P. aerophilum Nudix protein. [source]

X-ray investigation of gene-engineered human insulin crystallized from a solution containing polysialic acid

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2010
V. I. Timofeev
Attempts to crystallize the noncovalent complex of recombinant human insulin with polysialic acid were carried out under normal and microgravity conditions. Both crystal types belonged to the same space group, I213, with unit-cell parameters a = b = c = 77.365,Å, , = , = , = 90.00°. The reported space group and unit-cell parameters are almost identical to those of cubic insulin reported in the PDB. The results of X-ray studies confirmed that the crystals obtained were cubic insulin crystals and that they contained no polysialic acid or its fragments. Electron-density maps were calculated using X-ray diffraction sets from earth-grown and microgravity-grown crystals and the three-dimensional structure of the insulin molecule was determined and refined. The conformation and secondary-structural elements of the insulin molecule in different crystal forms were compared. [source]

Thermal Stability of Dehydrophenylalanine-Containing Model Peptides as Probed by Infrared Spectroscopy: a Case Study of an , -Helical and a 310 -Helical Peptide

CHEMISTRY & BIODIVERSITY, Issue 3 2006
Alka Gupta
Abstract The temperature-dependent secondary-structural changes in the two known helical model peptides Boc-Val-,Phe-Ala-Leu-Gly-OMe (1; , -helical) and Boc-Leu-Phe-Ala-,Phe-Leu-OMe (2; 310 -helical), which both comprise a single dehydrophenylalanine (,Phe) residue, were investigated by means of FT-IR spectroscopy (peptide film on KBr). Both the first-order and the better-resolved second-order derivative IR spectra of 1 and 2 were analyzed. The ,(NH) (3240,3340,cm,1), the Amide-I (1600,1700,cm,1), and the Amide-II (1510,1580,cm,1) regions of 1 and 2 showed significant differences in thermal-denaturation experiments (22°,144°), with the 310 -helical peptide (2) being considerably more stable. This observation was rationalized by different patterns and strengths of intramolecular H-bonds, and was qualitatively related to the different geometries of the peptides. Also, a fair degree of residual secondary-structural elements were found even in the ,denatured' states above 104° (1) or 134° (2). [source]