Common modifications of selenocysteine in selenoproteins

2019 ◽  
Vol 64 (1) ◽  
pp. 45-53 ◽  
Author(s):  
Elias S.J. Arnér
Keyword(s):  
Amino Acids ◽  
Covalent Binding ◽  
Physicochemical Characteristics ◽  
Redox Active

Abstract Selenocysteine (Sec), the sulfur-to-selenium substituted variant of cysteine (Cys), is the defining entity of selenoproteins. These are naturally expressed in many diverse organisms and constitute a unique class of proteins. As a result of the physicochemical characteristics of selenium when compared with sulfur, Sec is typically more reactive than Cys while participating in similar reactions, and there are also some qualitative differences in the reactivities between the two amino acids. This minireview discusses the types of modifications of Sec in selenoproteins that have thus far been experimentally validated. These modifications include direct covalent binding through the Se atom of Sec to other chalcogen atoms (S, O and Se) as present in redox active molecular motifs, derivatization of Sec via the direct covalent binding to non-chalcogen elements (Ni, Mb, N, Au and C), and the loss of Se from Sec resulting in formation of dehydroalanine. To understand the nature of these Sec modifications is crucial for an understanding of selenoprotein reactivities in biological, physiological and pathophysiological contexts.

Recent Advances in Photoredox Catalysis Enabled Functionalization of α-Amino Acids and Peptides: Concepts, Strategies and Mechanisms

Synthesis ◽  
2019 ◽  
Vol 51 (14) ◽  
pp. 2759-2791 ◽  
Author(s):  
Jian-Quan Liu ◽  
Andrey Shatskiy ◽  
Bryan S. Matsuura ◽  
Markus D. Kärkäs
Keyword(s):  
Amino Acids ◽  
Visible Light ◽  
Hypervalent Iodine ◽  
Amino Acid Residues ◽  
Photoredox Catalysis ◽  
Metal Catalysis ◽  
Specific Amino Acid ◽  
Recent Advances ◽  
Redox Active ◽  
Decarboxylative Coupling

The selective modification of α-amino acids and peptides constitutes a pivotal arena for accessing new peptide-based materials and therapeutics. In recent years, visible light photoredox catalysis has appeared as a powerful platform for the activation of small molecules via single-electron transfer events, allowing previously inaccessible reaction pathways to be explored. This review outlines the recent advances, mechanistic underpinnings, and opportunities of applying photoredox catalysis to the expansion of the synthetic repertoire for the modification of specific amino acid residues.1 Introduction2 Visible-Light-Mediated Functionalization of α-Amino Acids2.1 Decarboxylative Functionalization Involving Redox-Active Esters2.2 Direct Decarboxylative Coupling Strategies2.3 Hypervalent Iodine Reagents2.4 Dual Photoredox and Transition-Metal Catalysis2.5 Amination and Deamination Strategies3 Photoinduced Peptide Diversification3.1 Gese-Type Bioconjugation Methods3.2 Peptide Macrocyclization through Photoredox Catalysis3.3 Biomolecule Conjugation through Arylation3.4 C–H Functionalization Manifolds4 Conclusions and Outlook

Meat quality and chemical assessment of porcine longissimus dorsi within different muscle pH

2019 ◽  
Vol 59 (6) ◽  
pp. 1155 ◽  
Author(s):  
D. R. Kang ◽  
S. A. Belal ◽  
E. S. R. Cho ◽  
H. N. Kang ◽  
J. H. Jung ◽  
...  
Keyword(s):  
Amino Acids ◽  
Adenosine Diphosphate ◽  
Physicochemical Characteristics ◽  
Low Ph ◽  
Eating Quality ◽  
Longissimus Dorsi ◽  
Pork Quality ◽  
Isoleucine Leucine ◽  
High Ph ◽  
Longissimus Dorsi Muscle

This study was carried out to investigate the influence of pH on the Berkshire’s pork longissimus dorsi muscle, by comparing physicochemical characteristics in a high pH group (5.92 ± 0.02) and a low pH group (5.55 ± 0.03) on the basis of muscle pH24 h post-mortem. Fifteen pigs were assigned to each group (n = 15). The low pH group showed higher filter-paper fluid uptake, cooking loss and National Pork Producers Council marbling scores but did not significantly differ from the high pH group (P > 0.05). The low pH group also showed higher Commission International de l’Eclairage L* and b*, drip loss, and shearing forces were significantly different from the high pH group. However, Commission International de l’Eclairage meat colour value (a*) and National Pork Producers Council colour were higher in the high pH group. The content of glutamic acid, threonine, and serine amino acids associated with a good flavour was higher in the high pH group. Also, amino acids associated with a bitter or poor flavour, such as valine, isoleucine, leucine, tyrosine, and histidine, was higher in the high pH group as well. The taste of umami was significantly (P < 0.01) higher in the high pH group. Levels of the nucleotide compounds hypoxanthine and inosine tended to be higher (P < 0.05) in the high pH group, whereas adenosine diphosphate levels were increased in the low pH group (P < 0.05). It is concluded that pH of pork could be a good indicator of pork quality and related to factors influencing pork eating quality. As pH of pork is not only positively associated with physical traits of pork but also closely related to chemical traits of which higher free amino acids and nucleotides enhance pork quality.

Covalent binding of peroxidized linoleic acid to protein and amino acids as models for lipofuscin formation

Lipids ◽  
1982 ◽  
Vol 17 (12) ◽  
pp. 878-883 ◽  
Author(s):  
Hiroyuki Shimasaki ◽  
Nobuo Ueta ◽  
O. S. Privett
Keyword(s):  
Amino Acids ◽  
Linoleic Acid ◽  
Covalent Binding

Hymenolepis diminuta: The Microbial Fauna, Nutritional Gradients, and Physicochemical Characteristics of the Small Intestine of Uninfected and Parasitized Rats

1971 ◽  
Vol 49 (11) ◽  
pp. 972-984 ◽  
Author(s):  
D. F. Mettrick
Keyword(s):  
Escherichia Coli ◽  
Amino Acids ◽  
Small Intestine ◽  
Trichloroacetic Acid ◽  
Inverse Correlation ◽  
Physicochemical Characteristics ◽  
Hymenolepis Diminuta ◽  
Soluble Carbohydrate ◽  
Molar Ratios ◽  
Number Of Microorganisms

In uninfected rats the amount of trichloroacetic acid (TCA) soluble and insoluble carbohydrate in the small intestine declined steadily from duodenum to ileum. In rats infected with 10 16-day-old Hymenolepis diminuta these gradients were reversed and there was a 54% increase in the amount of TCA-soluble carbohydrate, and a 110% increase in the amount of glucose present in the luminal contents.In uninfected rats the amounts of TCA-soluble and -insoluble nitrogen and of total lipid in the small intestine were considerably more than in the intestine of infected rats. The differences may represent utilization by the worms of these nutrients.In parasitized rats the concentrations and molar ratios of the amino acids of the intestinal amino acid pool were significantly different (P < 0.001) in every region of the gut from those in uninfected animals.The intestinal pH of parasitized rats was lower than that in uninfected rats, and the pH gradient showed an inverse correlation with worm biomass and lactic acid distribution.The number of microorganisms present in the small intestine and colon of parasitized rats was less than half that in uninfected animals. Escherichia coli and the coliforms showed the greatest decrease in numbers. Other common aerobes were also markedly reduced in number. Anaerobic enterococci and yeasts were absent in the parasitized animals; anaerobic streptococci and micrococci were restricted to the ileum.

scholarly journals Importance of Highly Conserved Peptide Sites of Human Cytomegalovirus gO for Formation of the gH/gL/gO Complex

2016 ◽  
Vol 91 (1) ◽  
Author(s):  
Cora Stegmann ◽  
Mohamed E. A. Abdellatif ◽  
Kerstin Laib Sampaio ◽  
Paul Walther ◽  
Christian Sinzger
Keyword(s):  
Amino Acids ◽  
Complex Formation ◽  
Human Cytomegalovirus ◽  
Covalent Binding ◽  
Viral Envelope ◽  
Intermediate Phenotype ◽  
Proper Function ◽  
Target Cells ◽  
Trimeric Complex ◽  
Conserved Amino Acids

ABSTRACT The glycoprotein O (gO) is betaherpesvirus specific. Together with the viral glycoproteins H and L, gO forms a covalent trimeric complex that is part of the viral envelope. This trimer is crucial for cell-free infectivity of human cytomegalovirus (HCMV) but dispensable for cell-associated spread. We hypothesized that the amino acids that are conserved among gOs of different cytomegaloviruses are important for the formation of the trimeric complex and hence for efficient virus spread. In a mutational approach, nine peptide sites, containing all 13 highly conserved amino acids, were analyzed in the context of HCMV strain TB40-BAC4 with regard to infection efficiency and formation of the gH/gL/gO complex. Mutation of amino acids (aa) 181 to 186 or aa 193 to 198 resulted in the loss of the trimer and a complete small-plaque phenotype, whereas mutation of aa 108 or aa 249 to 254 caused an intermediate phenotype. While individual mutations of the five conserved cysteines had little impact, their relevance was revealed in a combined mutation, which abrogated both complex formation and cell-free infectivity. C343 was unique, as it was sufficient and necessary for covalent binding of gO to gH/gL. Remarkably, however, C218 together with C167 rescued infectivity in the absence of detectable covalent complex formation. We conclude that all highly conserved amino acids contribute to the function of gO to some extent but that aa 181 to 198 and cysteines 343, 218, and 167 are particularly relevant. Surprisingly, covalent binding of gO to gH/gL is required neither for its incorporation into virions nor for proper function in cell-free infection. IMPORTANCE Like all herpesviruses, the widespread human pathogen HCMV depends on glycoproteins gB, gH, and gL for entry into target cells. Additionally, gH and gL have to bind gO in a trimeric complex for efficient cell-free infection. Homologs of gO are shared by all cytomegaloviruses, with 13 amino acids being highly conserved. In a mutational approach we analyzed these amino acids to elucidate their role in the function of gO. All conserved amino acids contributed either to formation of the trimeric complex or to cell-free infection. Notably, these two phenotypes were not inevitably linked as the mutation of a charged cluster in the center of gO abrogated cell-free infection while trimeric complexes were still being formed. Cysteine 343 was essential for covalent binding of gO to gH/gL; however, noncovalent complex formation in the absence of cysteine 343 also allowed for cell-free infectivity.

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