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Residues Critical (residue + critical)

Distribution by Scientific Domains

Chemistry	66%
Life Sciences	33%

Selected Abstracts

Studies on a Tyr residue critical for the binding of coenzyme and substrate in mouse 3(17),-hydroxysteroid dehydrogenase (AKR1C21): structure of the Y224D mutant enzyme

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2010
Urmi Dhagat
Mouse 3(17),-hydroxysteroid dehydrogenase (AKR1C21) is the only aldo,keto reductase that catalyzes the stereospecific reduction of 3- and 17-ketosteroids to the corresponding 3(17),-hydroxysteroids. The Y224D mutation of AKR1C21 reduced the Km value for NADP(H) by up to 80-fold and completely reversed the 17, stereospecificity of the enzyme. The crystal structure of the Y224D mutant at 2.3,Å resolution revealed that the mutation resulted in a change in the conformation of the flexible loop B, including the V-shaped groove, which is a unique feature of the active-site architecture of wild-type AKR1C21 and is formed by the side chains of Tyr224 and Trp227. Furthermore, mutations (Y224F and Q222N) of residues involved in forming the safety belt for binding of the coenzyme showed similar alterations in kinetic constants for 3,-hydroxy/3-ketosteroids and 17-hydroxy/ketosteroids compared with the wild type. [source]

Actinorhodopsins: proteorhodopsin-like gene sequences found predominantly in non-marine environments

ENVIRONMENTAL MICROBIOLOGY, Issue 4 2008
Adrian K. Sharma
Summary Proteorhodopsins are light-energy-harvesting transmembrane proteins encoded by genes recently discovered in the surface waters of the world's oceans. Metagenomic data from the Global Ocean Sampling expedition (GOS) recovered 2674 proteorhodopsin-related sequences from 51 aquatic samples. Four of these samples were from non-marine environments, specifically, Lake Gatun within the Panama Canal, Delaware Bay and Chesapeake Bay and the Punta Cormorant Lagoon in Ecuador. Rhodopsins related to but phylogenetically distinct from most sequences designated proteorhodopsins were present at all four of these non-marine sites and comprised three different clades that were almost completely absent from marine samples. Phylogenomic analyses of genes adjacent to those encoding these novel rhodopsins suggest affiliation to the Actinobacteria, and hence we propose to name these divergent, non-marine rhodopsins ,actinorhodopsins'. Actinorhodopsins conserve the acidic amino acid residues critical for proton pumping and their genes lack genomic association with those encoding photo-sensory transducer proteins, thus supporting a putative ion pumping function. The ratio of recA and radA to rhodopsin genes in the different environment types sampled within the GOS indicates that rhodopsins of one type or another are abundant in microbial communities in freshwater, estuarine and lagoon ecosystems, supporting an important role for these photosystems in all aquatic environments influenced by sunlight. [source]

Identification of residues critical for toxicity in Clostridium perfringens phospholipase C, the key toxin in gas gangrene

FEBS JOURNAL, Issue 16 2000
Alberto Alape-Girón
Clostridium perfringens phospholipase C (PLC), also called ,-toxin, is the major virulence factor in the pathogenesis of gas gangrene. The toxic activities of genetically engineered ,-toxin variants harboring single amino-acid substitutions in three loops of its C-terminal domain were studied. The substitutions were made in aspartic acid residues which bind calcium, and tyrosine residues of the putative membrane-interacting region. The variants D269N and D336N had less than 20% of the hemolytic activity and displayed a cytotoxic potency 103 -fold lower than that of the wild-type toxin. The variants in which Tyr275, Tyr307, and Tyr331 were substituted by Asn, Phe, or Leu had 11,73% of the hemolytic activity and exhibited a cytotoxic potency 102 - to 105 -fold lower than that of the wild-type toxin. The results demonstrated that the sphingomyelinase activity and the C-terminal domain are required for myotoxicity in vivo and that the variants D269N, D336N, Y275N, Y307F, and Y331L had less than 12% of the myotoxic activity displayed by the wild-type toxin. This work therefore identifies residues critical for the toxic activities of C. perfringens PLC and provides new insights toward understanding the mechanism of action of this toxin at a molecular level. [source]

The mosquito ribonucleotide reductase R2 gene: ultraviolet light induces expression of a novel R2 variant with an internal amino acid deletion

INSECT MOLECULAR BIOLOGY, Issue 3 2004
G. Jayachandran
Abstract Using RT-PCR, we examined expression of the ribonucleotide reductase R2 subunit (RNR-R2) in Aedes albopictus mosquito cells after treatment with ultraviolet light (UV). In control cells, a predominant band at 1.2 kb corresponded to the full-length cDNA. A smaller 650 bp band was unique to UV-treated cells. Sequence analysis showed that the 650 bp band encoded a protein with an internal deletion of 179 amino acids, relative to Ae. albopictus RNR-R2. The N-terminal twenty amino acids were identical between AalRNR-R2 and Aal,R2; downstream of the deletion, the proteins differed at only four residues. In Aal,R2, the internal deletion spanned five residues critical to RNR-R2 enzymatic activity, including a key tyrosine residue that generates an essential free radical. The full-length 46 kDa and truncated 25 kDa RNR-R2 proteins were shown to be expressed on Western blots, and to differ in their subcellular localization. Similarly, expression of the two proteins was differentially regulated during the cell cycle, and expression of Aal,R2 predominated after UV treatment. Aal,R2 resembled a human RNR-R2 variant called p53R2, which was induced by agents that damage DNA. As was the case with p53R2 and its antisense RNA, levels of Aal,R2 were diminished after treatment of mosquito cells with RNAi corresponding to p53 from Drosophila melanogaster. Examination of the AalRNR-R2 homologue in the Anopheles gambiae genome suggested that Aal,R2 resulted from precise splicing between Exons 1, 4 and 5, eliminating Exons 2 and 3. The likelihood that Aal,R2 is a non-enzymatic, functional participant in DNA metabolism is suggested by enhancement of DNA repair in an in vitro system and by the presence of a similar gene (rnr4) in yeast. [source]

Mutation of residues critical for benzohydroxamic acid binding to horseradish peroxidase isoenzyme C

BIOPOLYMERS, Issue 5 2001
Barry D. Howes
Abstract Aromatic substrate binding to peroxidases is mediated through hydrophobic and hydrogen bonding interactions between residues on the distal side of the heme and the substrate molecule. The effects of perturbing these interactions are investigated by an electronic absorption and resonance Raman study of benzohydroxamic acid (BHA) binding to a series of mutants of horseradish peroxidase isoenzyme C (HRPC). In particular, the Phe179 , Ala, His42 , Glu variants and the double mutant His42 , Glu:Arg38 , Leu are studied in their ferric state at pH 7 with and without BHA. A comparison of the data with those previously reported for wild-type HRPC and other distal site mutants reaffirms that in the resting state mutation of His42 leads to an increase of 6-coordinate aquo heme forms at the expense of the 5-coordinate heme state, which is the dominant species in wild-type HRPC. The His42Glu:Arg38Leu double mutant displays an enhanced proportion of the pentacoordinate heme state, similar to the single Arg38Leu mutant. The heme spin states are insensitive to mutation of the Phe179 residue. The BHA complexes of all mutants are found to have a greater amount of unbound form compared to the wild-type HRPC complex. It is apparent from the spectral changes induced on complexation with BHA that, although Phe179 provides an important hydrophobic interaction with BHA, the hydrogen bonds formed between His42 and, in particular, Arg38 and BHA assume a more critical role in the binding of BHA to the resting state. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 261,267, 2001 [source]