Crosstalk between the Arg/N-end and Ac/N-end rule

X1165Ysciescopu

N-Terminal Acetylation-Targeted N-End Rule Proteolytic System: The Ac/N-End Rule Pathway

Although N-terminal acetylation (Nt-acetylation) is a pervasive protein modification in eukaryotes, its general functions in a majority of proteins are poorly understood. In 2010, it was discovered that Nt-acetylation creates a specific protein degradation signal that is targeted by a new class of the N-end rule proteolytic system, called the Ac/N-end rule pathway. Here, we review recent advances in our understanding of the mechanism and biological functions of the Ac/N-end rule pathway, and its crosstalk with the Arg/N-end rule pathway (the classical N-end rule pathway).112011Ysciescopuskc

Candida albicans pathogenicity mechanisms

Peer reviewedPublisher PD

The N-terminal methionine of cellular proteins as a degradation signal

The Arg/N-end rule pathway targets for degradation proteins that bear specific unacetylated N-terminal residues while the Ac/N-end rule pathway targets proteins through their N-infinity-terminally acetylated (Nt-acetylated) residues. Here, we show that Ubr1, the ubiquitin ligase of the Arg/N-end rule pathway, recognizes unacetylated N-terminal methionine if it is followed by a hydrophobic residue. This capability of Ubr1 expands the range of substrates that can be targeted for degradation by the Arg/N-end rule pathway because virtually all nascent cellular proteins bear N-terminal methionine. We identified Msn4, Sry1, Arl3, and Pre5 as examples of normal or misfolded proteins that can be destroyed through the recognition of their unacetylated N-terminal methionine. Inasmuch as proteins bearing the Nt-acetylated N-terminal methionine residue are substrates of the Ac/N-end rule pathway, the resulting complementarity of the Arg/N-end rule and Ac/N-end rule pathways enables the elimination of protein substrates regardless of acetylation state of N-terminal methionine in these substrates.X117863Ysciescopu

Degradation of Serotonin N-Acetyltransferase, a Circadian Regulator, by the N-end Rule Pathway

Serotonin N-acetyltransferase (AANAT) converts serotonin to N-acetylserotonin (NAS), a distinct biological regulator and the immediate precursor of melatonin, a circulating hormone that influences circadian processes, including sleep. N-terminal sequences of AANAT enzymes vary among vertebrates. Mechanisms that regulate the levels of AANAT are incompletely understood. Previous findings were consistent with the possibility that AANAT may be controlled through its degradation by the N-end rule pathway. By expressing the rat and human AANATs and their mutants not only in mammalian cells but also in the yeast Saccharomyces cerevisiae, and by taking advantage of yeast genetics, we show here that two complementary forms of rat AANAT are targeted for degradation by two complementary branches of the N-end rule pathway. Specifically, the N-terminally acetylated (Nt-acetylated) Ac-AANAT is destroyed through the recognition of its Nt-acetylated N-terminal Met residue by the Ac/N-end rule pathway, whereas the non-Nt-acetylated AANAT is targeted by the Arg/N-end rule pathway, which recognizes the unacetylated N-terminal Met-Leu sequence of rat AANAT. We also show, by constructing lysine-to-arginine mutants of rat AANAT, that its degradation is mediated by polyubiquitylation of its Lys residue(s). Human AANAT, whose N-terminal sequence differs from that of rodent AANATs, is longer-lived than its rat counterpart and appears to be refractory to degradation by the N-end rule pathway. Together, these and related results indicate both a major involvement of the N-end rule pathway in the control of rodent AANATs and substantial differences in the regulation of rodent and human AANATs that stem from differences in their N-terminal sequences.1141Ysciescopu

Crystal Structure of the Rad3/XPD regulatory domain of Ssl1/p44

The Ssl1/p44 subunit is a core component of the yeast/mammalian general transcription factor TFIIH, which is involved in transcription and DNA repair. Ssl1/p44 binds to and stimulates the Rad3/XPD helicase activity of TFIIH. To understand the helicase stimulatory mechanism of Ssl1/p44, we determined the crystal structure of the N-terminal regulatory domain of Ssl1 from Saccharomyces cerevisiae. Ssl1 forms a von Willebrand factor A fold in which a central six-stranded beta-sheet is sandwiched between three alpha helices on both sides. Structural and biochemical analyses of Ssl1/p44 revealed that the beta 4-alpha 5 loop, which is frequently found at the interface between von Willebrand factor A family proteins and cellular counterparts, is critical for the stimulation of Rad3/XPD. Yeast genetics analyses showed that double mutation of Leu-239 and Ser-240 in the beta 4-alpha 5 loop of Ssl1 leads to lethality of a yeast strain, demonstrating the importance of the Rad3-Ssl1 interactions to cell viability. Here, we provide a structural model for the Rad3/XPD-Ssl1/p44 complex and insights into how the binding of Ssl1/p44 contributes to the helicase activity of Rad3/XPD and cell viability.X1165Ysciescopu

Placental Growth Factor-1 and -2 Induce Hyperplasia and Invasiveness of Primary Rheumatoid Synoviocytes

Inflammation-mediated oncogenesis has been implicated in a variety of cancer types. Rheumatoid synovial tissues can be viewed as a tumor-like mass, consisting of hyperplastic fibroblast-like synoviocytes (FLSs). FLSs of rheumatoid arthritis (RA) patients have promigratory and invasive characteristics, which may be caused by chronic exposure to genotoxic stimuli, including hypoxia and growth factors. We tested whether a transformed phenotype of RA-FLSs is associated with placental growth factor (PlGF), a representative angiogenic growth factor induced by hypoxia. In this study, we identified PlGF-1 and PlGF-2 as the major PlGF isoforms in RA-FLSs. Global gene expression profiling revealed that cell proliferation, apoptosis, angiogenesis, and cell migration were mainly represented by differentially expressed genes in RA-FLSs transfected with small interfering RNA for PlGF. Indeed, PlGF-deficient RA-FLSs showed a decrease in cell proliferation, migration, and invasion, but an increase in apoptotic death in vitro. PlGF gene overexpression resulted in the opposite effects. Moreover, exogeneous PlGF-1 and PlGF-2 increased survival, migration, and invasiveness of RA-FLSs by binding their receptors, Flt-1 and neuropilin-1, and upregulating the expression of antiapoptotic molecules, pErk and Bcl2. Knockdown of PlGF transcripts reduced RA-FLS proliferation in a xenotransplantation model. Collectively, in addition to their role for neovascularization, PlGF-1 and -2 promote proliferation, survival, migration, and invasion of RA-FLSs in an autocrine and paracrine manner. These results demonstrated how primary cells of mesenchymal origin acquired an aggressive and transformed phenotype. PlGF and its receptors thus offer new targets for anti-FLS therapy.1177Ysciescopu

RGO/Nylon-6 composite mat with unique structural features and electrical properties obtained from electrospinning and hydrothermal process

In this work, the reduced graphene oxide (RGO) sheets were effectively uploaded through nylon-6 fibers using combined process of electrospinning and hydrothermal treatment. Good dispersion of graphene oxide (GO) with nylon-6 solution could allow to upload GO sheets through nylon-6 fibers and facilitate the formation of spider-wave-like nano-nets during electrospinning. GO sheets present on/into nylon-6 spider-wave-like nano-nets were further reduced to RGO using hydrothermal treatment. The impregnated GO sheets into nylon-6 nanofibers and their reduction during hydrothermal treatment were confirmed by FE-SEM, TEM, FT-IR and Raman spectra. The electrical characteristics of pristine nylon-6, GO/nylon-6 and RGO/nylon-6 nanofibers were investigated and it was found that RGO/nylon-6 composite mat had better electrical conductivity than others. The formation of spider-wave-like nano-nets as well as indirect route of incorporation of RGO sheets on electrospun nylon-6 mat may open a new direction for future graphene/polymer electronics. © 2013 The Korean Fiber Society and Springer Science+Business Media Dordrecht