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Proteins and Proteomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
The operon consists of the following components: regulator gene, promoter gene (a relatively recent concept), operator gene, structural genes, repressor, corepressor, and inducer. For example, to synthesize β-galactosidase in E. coli, Jacob and Monod in 1961 proposed a model based on an inducible system which is also known as the operon model. An operon consists of an operator gene, which controls the activity of protein synthesis, and several structural genes that take part in the synthesis of proteins. In brief, the structural genes will synthesize mRNA under the operational control of an operator gene, which in turn is under the control of a repressor molecule synthesized by a regulator gene that is not a part of the operon (Figure 3.11).
Proteins and proteomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
The operon consists of the following components: regulator gene, promoter gene (a relatively recent concept), operator gene, structural genes, repressor, corepressor, and inducer. For example, to synthesize β-galactosidase in E. coli, Jacob and Monod in 1961 proposed a model based on inducible system, which is also known as operon model. An operon consists of an operator gene, which controls the activity of protein synthesis, and a number of structural genes, which take part in the synthesis of proteins. In brief, the structural genes will synthesize mRNA under the operational control of an operator gene, which in turn is under the control of a repressor molecule synthesized by a regulator gene, which is not a part of the operon (Figure 3.11).
Bioinspired Magnetic Nanoparticles for Biomedical Applications
Published in Nguyễn T. K. Thanh, Clinical Applications of Magnetic Nanoparticles, 2018
Each step is strictly controlled by complex machinery that is composed of a large number of genetic determinants. These responsible genes are located mostly within a gnenomic magnetosome island (MAI) that is composed of mamAB operon, felAB1, mms6 operon, mamGFDC operon and mamXY operon (Figure 4.1g).24–26 These operons are highly conserved in closely related Magnetospirillum magneticum. An operon is made up of several structural genes arranged under a common promoter and regulated by a common operator. Usually, these genes encode proteins working together in a metabolic pathway. The large (16–17 kb) mamAB operon contains several genes that play key roles in magnetosome biogenesis.27,28 Comprehensive functional analysis of MAI deletion mutants in M. magneticum AMB-1 shows that mamAB operons are encoded for factors important for magnetosome membrane biogenesis, for targeting of proteins in this compartment and for several steps of magnetite mineralization. For example, four conserved genes of mamI, mamL, mamQ and mamB in mamAB gene clusters are significantly important for inner membrane invagination and magnetosome vesicle formation. mamE is essential for localization of a subset of proteins in the magnetosome membrane. However, another four small operons encode nonessential proteins, including the putative iron transporters FeoAB1 and MamZ; the tubulin-like protein FtsZm; and the magnetotactic bacteria-specific proteins MamC (also known as Mms13), MamD (also known as Mms7), MamF, MamG, MamX, MamY, Mms6, MmsF, Mms36 and Mms48. These proteins have supplementary roles in regulating the size and shape of biomineralized magnetic nanocrystal.29–31
The enigma of environmental organoarsenicals: Insights and implications
Published in Critical Reviews in Environmental Science and Technology, 2022
Xi-Mei Xue, Chan Xiong, Masafumi Yoshinaga, Barry Rosen, Yong-Guan Zhu
The biosynthetic pathways for arsenosugars have not been studied well compared with those for simple methylarsenicals, probably because arsenosugars are identified mainly in marine macroalgae or animals, more complex systems than bacteria. However, the recent discovery that arsenosugars are produced by prokaryotic cyanobacteria has stimulated research on these systems (Xue et al., 2014, Xue et al., 2017a). Dimethylated arsenosugars are composed of a pentavalent dimethylarsinoy moiety and a 5′-deoxyriboside. Cells of the cyanobacterium Synechocystis sp. PCC 6803 produce arsenosugars when exposed to As(III), MAs(V) or DMAs(V). In contrast, cells in which the arsM gene was deleted produced arsenosugars only when incubated with DMAs(V), but not with either As(III) or MAs(V), suggesting that the ArsM is involved in arsenosugar biosynthesis via production of the precursor DMAs(III) (Xue et al., 2017b). In prokaryote genomes, multiple genes with related functions often form a cluster, or an operon, under the control of a single promoter. A gene adjacent to SsarsM (the arsM gene of Synechocystis sp. PCC 6803) has been termed SsarsS and is annotated to encode a radical SAM superfamily protein characterized by four iron-four sulfur ([4Fe-4S]) clusters and SAM-binding sites (Xue et al., 2019). Neither SsarsM nor an SsarsS mutant was able to produce arsenosugars, suggesting that both genes are necessary for the synthesis of arsenosugars. Recently, purified SsArsS was demonstrated to catalyze the formation of 5′-deoxy-5′-dimethylarsinoyladenosine (Table 1.23) by forming an adenosine radical (Fig. 1C) (Cheng et al., 2021). E. coli cells expressing both the SsarsM and SsarsS genes produced DMAs(V) and dimethylarsinoyl hydroxycarboxylic acid derivatives but not arsenosugars, suggesting that E. coli cells may degrade 5′-deoxy-5′-dimethylarsinoyladenosine (Xue et al., 2019). Dimethylarsinoylalchols (DMAE and thio-DMAE), dimethylarsinoyl-carboxylic acids (DMAA and thio-DMAA), and methylarsenicals (MAs(V) and DMAs(V)) have been detected in mammalian urine and feces after ingestion of arsenosugars (Francesconi et al., 2002). Bacteria may play a role in degradation of arsenosugars in animals. In contrast, Oxo-Gly was only converted into thio-Gly in an in vitro artificial gastrointestinal digestion system, indicating the complexity of degradation of arsenosugars (Hata et al., 2019). Microorganisms and enzymes involved in the pathway of arsenosugar degradation remains to be identified.