scholarly journals Removal of Potential Phosphorylation Sites does not Alter Creatine Transporter Response to PKC or Substrate Availability

2015 ◽  
Vol 37 (1) ◽  
pp. 353-360 ◽  
Author(s):  
Lucia Santacruz ◽  
Marcus D. Darrabie ◽  
Rajashree Mishra ◽  
Danny O. Jacobs
Keyword(s):  
Intracellular Signaling ◽  
Site Directed Mutagenesis ◽  
Phosphorylation Sites ◽  
Structural Elements ◽  
Substrate Availability ◽  
Bioinformatics Analyses ◽  
Creatine Transporter ◽  
Transporter Protein ◽  
Creatine Transport ◽  
Pkc Activation

Background: Creatine, Phosphocreatine, and creatine kinases, constitute an energy shuttle that links ATP production in mitochondria with cellular consumption sites. Myocytes and neurons cannot synthesize creatine and depend on uptake across the cell membrane by a specialized transporter to maintain intracellular creatine levels. Although recent studies have improved our understanding of creatine transport in cardiomyocytes, the structural elements underlying the creatine transporter protein regulation and the relevant intracellular signaling processes are unknown. Methods: The effects of pharmacological activation of kinases or phosphatases on creatine transport in cardiomyocytes in culture were evaluated. Putative phosphorylation sites in the creatine transporter protein were identified by bioinformatics analyses, and ablated using site-directed mutagenesis. Mutant transporter function and their responses to pharmacological PKC activation or changes in creatine availability in the extracellular environment, were evaluated. Results: PKC activation decreases creatine transport in cardiomyocytes in culture. Elimination of high probability potential phosphorylation sites did not abrogate responses to PKC activation or substrate availability. Conclusion: Modulation of creatine transport in cardiomyocytes is a complex process where phosphorylation at predicted sites in the creatine transporter protein does not significantly alter activity. Instead, non-classical structural elements in the creatine transporter and/or interactions with regulatory subunits may modulate its activity.

AMPK and substrate availability regulate creatine transport in cultured cardiomyocytes

2011 ◽  
Vol 300 (5) ◽  
pp. E870-E876 ◽  
Author(s):  
Marcus D. Darrabie ◽  
Antonio Jose Luis Arciniegas ◽  
Rajashree Mishra ◽  
Dawn E. Bowles ◽  
Danny O. Jacobs ◽  
...  
Keyword(s):  
Heart Failure ◽  
Energy Homeostasis ◽  
Cardiac Cells ◽  
Substrate Availability ◽  
Human Heart Failure ◽  
Positive Role ◽  
Creatine Transporter ◽  
Neonatal Cardiomyocytes ◽  
Transporter Protein ◽  
Creatine Transport

Profound alterations in myocellular creatine and phosphocreatine levels are observed during human heart failure. To maintain its intracellular creatine stores, cardiomyocytes depend upon a cell membrane creatine transporter whose regulation is not clearly understood. Creatine transport capacity in the intact heart is modulated by substrate availability, and it is reduced in the failing myocardium, likely adding to the energy imbalance that characterizes heart failure. AMPK, a key regulator of cellular energy homeostasis, acts by switching off energy-consuming pathways in favor of processes that generate energy. Our objective was to determine the effects of substrate availability and AMPK activation on creatine transport in cardiomyocytes. We studied creatine transport in rat neonatal cardiomyocytes and HL-1 cardiac cells expressing the human creatine transporter cultured in the presence of varying creatine concentrations and the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR). Transport was enhanced in cardiomyocytes following incubation in creatine-depleted medium or AICAR. The changes in transport were due to alterations in Vmax that correlated with changes in total and cell surface creatine transporter protein content. Our results suggest a positive role for AMPK in creatine transport modulation for cardiomyocytes in culture.

scholarly journals Ser-322 Is a Critical Site for PKC Regulation of the MDCKCell Taurine Transporter (pNCT)

1999 ◽  
Vol 10 (9) ◽  
pp. 1874-1879
Author(s):  
XIAOBIN HAN ◽  
ANDREA M. BUDREAU ◽  
RUSSELL W. CHESNEY
Keyword(s):  
Expression System ◽  
Site Directed Mutagenesis ◽  
Transport Activity ◽  
Wild Type ◽  
Taurine Transporter ◽  
Taurine Transport ◽  
Transporter Protein ◽  
Oocyte Expression System ◽  
Pkc Activation ◽  
Critical Site

Abstract. Previous studies have shown that the Madin—Darby canine kidney cell taurine transporter (pNCT) is downregulated by protein kinase C (PKC) activation. In this study, it is hypothesized that the highly conserved serine-322 (Ser-322) located in the fourth intracellular segment (S4) may play an important role in the function of taurine transporter, which is modulated by PKC phosphorylation. It is demonstrated that Ser-322 is the critical site of PKC phosphorylation, as determined by site-directed mutagenesis. When Ser-322 of pNCT was changed to alanine (S322A) and this mutant was evaluated in an oocyte expression system, taurine transport activity increased threefold compared with control (wild-type pNCT). Activation of PKC by the active phorbol ester 12-myristate 13-acetate did not influence taurine transport by mutant S322A. Kinetic analysis showed that the mutation of Ser-322 essentially changed the Vmax, rather than the Km, of the transporter. Mutation of all other PKC consensus sites did not affect transporter activity when expressed in the oocyte system. Western blot analysis showed that expression of taurine transporter protein was similar in oocytes injected with either wild-type or mutant pNCT cRNA, indicating that the enhanced taurine transport activity by mutant S322A was not caused by a greater amount of transporter expressed in the oocyte. Furthermore, this study demonstrated that the taurine transporter was phosphorylated after PKC activation, and this effect was not observed in mutant S322A. In conclusion, Ser-322 is critical in PKC regulation of taurine transporter activity. The steady-state taurine transporter activity is tightly controlled by endogenous PKC phosphorylation of Ser-322, which is located in the fourth intracellular segment of the taurine transporter.

Exposing cardiomyocytes to subclinical concentrations of doxorubicin rapidly reduces their creatine transport

2012 ◽  
Vol 303 (5) ◽  
pp. H539-H548 ◽  
Author(s):  
Marcus D. Darrabie ◽  
Antonio Jose Luis Arciniegas ◽  
Jose Gabriel Mantilla ◽  
Rajashree Mishra ◽  
Miguel Pinilla Vera ◽  
...  
Keyword(s):  
Cell Surface ◽  
Peak Plasma ◽  
Plasma Concentrations ◽  
Soft Tissue Sarcomas ◽  
Cardiac Cells ◽  
Early Event ◽  
Creatine Transporter ◽  
Transporter Protein ◽  
Creatine Uptake ◽  
Creatine Transport

Doxorubicin is commonly used to treat leukemia, lymphomas, and solid tumors, such as soft tissue sarcomas or breast cancer. A major side effect of doxorubicin therapy is dose-dependent cardiotoxicity. Doxorubicin's effects on cardiac energy metabolism are emerging as key elements mediating its toxicity. We evaluated the effect of doxorubicin on [14C]creatine uptake in rat neonatal cardiac myocytes and HL-1 murine cardiac cells expressing the human creatine transporter protein. A significant and irreversible decrease in creatine transport was detected after an incubation with 50–100 nmol/l doxorubicin. These concentrations are well below peak plasma levels (5 μmol/l) and within the ranges (25–250 nmol/l) for steady-state plasma concentrations reported after the administration of 15–90 mg/m2 doxorubicin for chemotherapy. The decrease in creatine transport was not solely because of increased cell death due to doxorubicin's cytotoxic effects. Kinetic analysis showed that doxorubicin decreased Vmax, Km, and creatine transporter protein content. Cell surface biotinylation experiments confirmed that the amount of creatine transporter protein present at the cell surface was reduced. Cardiomyocytes rely on uptake by a dedicated creatine transporter to meet their intracellular creatine needs. Our findings show that the cardiomyocellular transport capacity for creatine is substantially decreased by doxorubicin administration and suggest that this effect may be an important early event in the pathogenesis of doxorubicin-mediated cardiotoxicity.

scholarly journals Potential Phosphorylation of Viral Nonstructural Protein 1 in Dengue Virus Infection

Viruses ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1393
Author(s):  
Thanyaporn Dechtawewat ◽  
Sittiruk Roytrakul ◽  
Yodying Yingchutrakul ◽  
Sawanya Charoenlappanit ◽  
Bunpote Siridechadilok ◽  
...  
Keyword(s):  
Dengue Virus ◽  
Nonstructural Protein ◽  
Antiviral Drug ◽  
Denv Infection ◽  
Site Directed Mutagenesis ◽  
Phosphorylation Sites ◽  
Post Translational Modification ◽  
Multifunctional Protein ◽  
Nonstructural Protein 1 ◽  
Underlying Mechanisms

Dengue virus (DENV) infection causes a spectrum of dengue diseases that have unclear underlying mechanisms. Nonstructural protein 1 (NS1) is a multifunctional protein of DENV that is involved in DENV infection and dengue pathogenesis. This study investigated the potential post-translational modification of DENV NS1 by phosphorylation following DENV infection. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), 24 potential phosphorylation sites were identified in both cell-associated and extracellular NS1 proteins from three different cell lines infected with DENV. Cell-free kinase assays also demonstrated kinase activity in purified preparations of DENV NS1 proteins. Further studies were conducted to determine the roles of specific phosphorylation sites on NS1 proteins by site-directed mutagenesis with alanine substitution. The T27A and Y32A mutations had a deleterious effect on DENV infectivity. The T29A, T230A, and S233A mutations significantly decreased the production of infectious DENV but did not affect relative levels of intracellular DENV NS1 expression or NS1 secretion. Only the T230A mutation led to a significant reduction of detectable DENV NS1 dimers in virus-infected cells; however, none of the mutations interfered with DENV NS1 oligomeric formation. These findings highlight the importance of DENV NS1 phosphorylation that may pave the way for future target-specific antiviral drug design.

scholarly journals Interactions between Multiple Phosphorylation Sites in the Inactivation Particle of a K+ Channel

1998 ◽  
Vol 112 (1) ◽  
pp. 71-84 ◽  
Author(s):  
Edward J. Beck ◽  
Roger G. Sorensen ◽  
Simon J. Slater ◽  
Manuel Covarrubias
Keyword(s):  
Tertiary Structure ◽  
Site Directed Mutagenesis ◽  
K Channel ◽  
Phosphorylation Sites ◽  
Free Energies ◽  
Channel Inactivation ◽  
Recovery From Inactivation ◽  
Pkc Isoforms ◽  
Inactivation Gating ◽  
Rate Of Recovery

Protein kinase C inhibits inactivation gating of Kv3.4 K+ channels, and at least two NH2-terminal serines (S15 and S21) appeared involved in this interaction (Covarrubias et al. 1994. Neuron. 13:1403–1412). Here we have investigated the molecular mechanism of this regulatory process. Site-directed mutagenesis (serine → alanine) revealed two additional sites at S8 and S9. The mutation S9A inhibited the action of PKC by ∼85%, whereas S8A, S15A, and S21A exhibited smaller reductions (41, 35, and 50%, respectively). In spite of the relatively large effects of individual S → A mutations, simultaneous mutation of the four sites was necessary to completely abolish inhibition of inactivation by PKC. Accordingly, a peptide corresponding to the inactivation domain of Kv3.4 was phosphorylated by specific PKC isoforms, but the mutant peptide (S[8,9,15,21]A) was not. Substitutions of negatively charged aspartate (D) for serine at positions 8, 9, 15, and 21 closely mimicked the effect of phosphorylation on channel inactivation. S → D mutations slowed the rate of inactivation and accelerated the rate of recovery from inactivation. Thus, the negative charge of the phosphoserines is an important incentive to inhibit inactivation. Consistent with this interpretation, the effects of S8D and S8E (E = Glu) were very similar, yet S8N (N = Asn) had little effect on the onset of inactivation but accelerated the recovery from inactivation. Interestingly, the effects of single S → D mutations were unequal and the effects of combined mutations were greater than expected assuming a simple additive effect of the free energies that the single mutations contribute to impair inactivation. These observations demonstrate that the inactivation particle of Kv3.4 does not behave as a point charge and suggest that the NH2-terminal phosphoserines interact in a cooperative manner to disrupt inactivation. Inspection of the tertiary structure of the inactivation domain of Kv3.4 revealed the topography of the phosphorylation sites and possible interactions that can explain the action of PKC on inactivation gating.

scholarly journals Blakeslea trispora Photoreceptors: Identification and Functional Analysis

2020 ◽  
Vol 86 (8) ◽  
Author(s):  
Wei Luo ◽  
Chao Xue ◽  
Yuzheng Zhao ◽  
Huili Zhang ◽  
Zhiming Rao ◽  
...  
Keyword(s):  
Large Scale ◽  
Binding Domain ◽  
Site Directed Mutagenesis ◽  
Flavin Mononucleotide ◽  
Blakeslea Trispora ◽  
Scale Production ◽  
Bioinformatics Analyses ◽  
Content Type ◽  
Flavin Binding

ABSTRACT Blakeslea trispora is an industrial fungal species used for large-scale production of carotenoids. However, B. trispora light-regulated physiological processes, such as carotenoid biosynthesis and phototropism, are not fully understood. In this study, we isolated and characterized three photoreceptor genes, btwc-1a, btwc-1b, and btwc-1c, in B. trispora. Bioinformatics analyses of these genes and their protein sequences revealed that the functional domains (PAS/LOV [Per-ARNT-Sim/light-oxygen-voltage] domain and zinc finger structure) of the proteins have significant homology to those of other fungal blue-light regulator proteins expressed by Mucor circinelloides and Neurospora crassa. The photoreceptor proteins were synthesized by heterologous expression in Escherichia coli. The chromogenic groups consisting of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) were detected to accompany BTWC-1 proteins by using high-performance liquid chromatography (HPLC) and fluorescence spectrometry, demonstrating that the proteins may be photosensitive. The absorbance changes of the purified BTWC-1 proteins seen under dark and light conditions indicated that they were light responsive and underwent a characteristic photocycle by light induction. Site-directed mutagenesis of the cysteine residual (Cys) in BTWC-1 did not affect the normal expression of the protein in E. coli but did lead to the loss of photocycle response, indicating that Cys represents a flavin-binding domain for photon detection. We then analyzed the functions of BTWC-1 proteins by complementing btwc-1a, btwc-1b, and btwc-1c into the counterpart knockout strains of M. circinelloides for each mcwc-1 gene. Transformation of the btwc-1a complement into mcwc-1a knockout strains restored the positive phototropism, while the addition of btwc-1c complement remedied the deficiency of carotene biosynthesis in the mcwc-1c knockout strains under conditions of illumination. These results indicate that btwc-1a and btwc-1c are involved in phototropism and light-inducible carotenogenesis. Thus, btwc-1 genes share a conserved flavin-binding domain and act as photoreceptors for control of different light transduction pathways in B. trispora. IMPORTANCE Studies have confirmed that light-regulated carotenogenesis is prevalent in filamentous fungi, especially in mucorales. However, few investigations have been done to understand photoinduced synthesis of carotenoids and related mechanisms in B. trispora, a well-known industrial microbial strains. In the present study, three photoreceptor genes in B. trispora were cloned, expressed, and characterized by bioinformatics and photoreception analyses, and then in vivo functional analyses of these genes were constructed in M. circinelloides. The results of this study will lead to a better understanding of photoreception and light-regulated carotenoid synthesis and other physiological responses in B. trispora.

Molecular characterisation of Tyr530Ser and IVS16–1G>T mutations causing severe factor V deficiency

2010 ◽  
Vol 104 (09) ◽  
pp. 536-543 ◽  
Author(s):  
Weidong Zheng ◽  
Yanhui Liu ◽  
Ying Luo ◽  
Zhihong Chen ◽  
Yan Wang ◽  
...  
Keyword(s):  
Deletion Mutant ◽  
Coagulation Factor ◽  
Underlying Mechanism ◽  
Procoagulant Activity ◽  
Site Directed Mutagenesis ◽  
Factor V ◽  
Wild Type ◽  
Site Mutation ◽  
Bioinformatics Analyses ◽  
Mutant Transcript

SummaryOur previous study reported a missense mutation (Tyr530Ser) and a splicing site mutation (IVS16–1G>T) in blood coagulation factor V (FV) gene in a two-year-old Chinese boy. However, the linkage between the mutations and severe FV deficiency and the underlying mechanism has not been elucidated. The present study was designed to investigate the effect of the two mutations and the possible pathogenetic mechanism. FV procoagulant activity showed tremendous decrease in the patient with two mutations. The bioinformatics analyses predicted that IVS16–1G>T mutation may cause the entire exon 17 of FV to be skipped in transcription and thereby result in a deletion mutant. To confirm the predicted results, the fragment of exon 16 to exon 18 containing IVS16–1G>T mutation was obtained by PCR and site-directed mutagenesis. IVS16–1G>T mutant and wild-type constructs were transfected into COS-7 cells. Sequence analysis showed that mutant transcript lacked the entire 180-bp length of exon 17. Moreover, compared to wild-type, the expression of the two mutant proteins was decreased and the procoagulant activity was also reduced when the deletion mutant cDNA and Tyr530Ser site mutant cDNA were transfected into COS-7 cells, respectively. Our results indicate that Tyr530Ser and IVS16–1G>T could be separately responsible for severe FV deficiency, while the phenotype in the proband could be caused by the combination effect of the two defects.

scholarly journals Crystal structure of the capsular polysaccharide synthesizing protein CapE of Staphylococcus aureus

2013 ◽  
Vol 33 (3) ◽  
Author(s):  
Takamitsu Miyafusa ◽  
Jose M. M. Caaveiro ◽  
Yoshikazu Tanaka ◽  
Martin E. Tanner ◽  
Kouhei Tsumoto
Keyword(s):  
Staphylococcus Aureus ◽  
Conformational Changes ◽  
Capsular Polysaccharide ◽  
Site Directed Mutagenesis ◽  
Structural Elements ◽  
Contact Interface ◽  
Protein Subunits ◽  
Polysaccharide Synthesis ◽  
Substrate Binding Domain ◽  
Primary Sequence Alignment

Enzymes synthesizing the bacterial CP (capsular polysaccharide) are attractive antimicrobial targets. However, we lack critical information about the structure and mechanism of many of them. In an effort to reduce that gap, we have determined three different crystal structures of the enzyme CapE of the human pathogen Staphylococcus aureus. The structure reveals that CapE is a member of the SDR (short-chain dehydrogenase/reductase) super-family of proteins. CapE assembles in a hexameric complex stabilized by three major contact surfaces between protein subunits. Turnover of substrate and/or coenzyme induces major conformational changes at the contact interface between protein subunits, and a displacement of the substrate-binding domain with respect to the Rossmann domain. A novel dynamic element that we called the latch is essential for remodelling of the protein–protein interface. Structural and primary sequence alignment identifies a group of SDR proteins involved in polysaccharide synthesis that share the two salient features of CapE: the mobile loop (latch) and a distinctive catalytic site (MxxxK). The relevance of these structural elements was evaluated by site-directed mutagenesis.

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