scholarly journals Human thrombopoietin structure–function relationships: identification of functionally important residues

1998 ◽  
Vol 333 (3) ◽  
pp. 729-734 ◽  
Author(s):  
Alexandre JAGERSCHMIDT ◽  
Valérie FLEURY ◽  
Marielle ANGER-LEROY ◽  
Corinne THOMAS ◽  
Magali AGNEL ◽  
...  
Keyword(s):  
Biological Effects ◽  
Expression System ◽  
Receptor Activation ◽  
Glycosylation Site ◽  
Eukaryotic Expression ◽  
Site Directed Mutagenesis ◽  
Receptor Dimerization ◽  
Haematopoietic Growth Factor ◽  
Proliferation And Differentiation ◽  
Receptor Interactions

Thrombopoietin (TPO) is a haematopoietic growth factor responsible for megakaryocyte progenitor proliferation and differentiation. It belongs to the four-helix-bundle cytokine family and exerts its biological effects through binding to a specific receptor, c-Mpl. With the use of site-directed mutagenesis we have generated 20 TPO mutants. Each of the TPO mutants was produced in a eukaryotic expression system and the mutants' ability to induce the proliferation of factor-dependent c-Mpl-expressing megakaryoblastic M-O7e cells was compared with that of wild-type TPO. Among the mutations studied, 10 lead to a significant decrease in TPO bioactivity. Of these ten residues, three are located in helix A of the protein (Arg10, Lys14 and Arg17) and four in helix D (His133, Gln132, Lys138 and Phe141), indicating that in TPO, as in other cytokines, these two helices are important for functional cytokine/receptor interactions. Surprisingly, mutant Arg10 → Ala (R10A) lacked any proliferative activity, despite the fact that this mutation was recently reported to have no effect on TPO/c-Mpl binding in a TPO phage ELISA [Pearce, Potts, Presta, Bald, Fendly and Wells (1997) J. Biol. Chem. 272, 20595–20602]. The lack of M-O7e proliferation is probably due to an inability of R10A mutant to promote receptor dimerization and thus receptor activation. Moreover we found that the Arg10 and Arg17 residues of TPO seem to be specific determinants for TPO/c-Mpl recognition. We also demonstrate that the O-glycosylation site located at position 110 of TPO is not necessary for the bioactivity of the cytokine.

scholarly journals N-Glycosylation Improves the Pepsin Resistance of Histidine Acid Phosphatase Phytases by Enhancing Their Stability at Acidic pHs and Reducing Pepsin's Accessibility to Its Cleavage Sites

2015 ◽  
Vol 82 (4) ◽  
pp. 1004-1014 ◽  
Author(s):  
Canfang Niu ◽  
Huiying Luo ◽  
Pengjun Shi ◽  
Huoqing Huang ◽  
Yaru Wang ◽  
...  
Keyword(s):  
Acid Phosphatase ◽  
Biochemical Characterization ◽  
Animal Feed ◽  
Glycosylation Site ◽  
Site Directed Mutagenesis ◽  
Acidic Ph ◽  
Cleavage Sites ◽  
Ph Optimum ◽  
Content Type ◽  
Histidine Acid Phosphatase

ABSTRACTN-Glycosylation can modulate enzyme structure and function. In this study, we identified two pepsin-resistant histidine acid phosphatase (HAP) phytases fromYersinia kristensenii(YkAPPA) andYersinia rohdei(YrAPPA), each having anN-glycosylation motif, and one pepsin-sensitive HAP phytase fromYersinia enterocolitica(YeAPPA) that lacked anN-glycosylation site. Site-directed mutagenesis was employed to construct mutants by altering theN-glycosylation status of each enzyme, and the mutant and wild-type enzymes were expressed inPichia pastorisfor biochemical characterization. Compared with those of theN-glycosylation site deletion mutants andN-deglycosylated enzymes, allN-glycosylated counterparts exhibited enhanced pepsin resistance. Introduction of theN-glycosylation site into YeAPPA as YkAPPA and YrAPPA conferred pepsin resistance, shifted the pH optimum (0.5 and 1.5 pH units downward, respectively) and improved stability at acidic pH (83.2 and 98.8% residual activities at pH 2.0 for 1 h). Replacing the pepsin cleavage sites L197 and L396 in the immediate vicinity of theN-glycosylation motifs of YkAPPA and YrAPPA with V promoted their resistance to pepsin digestion when produced inEscherichia colibut had no effect on the pepsin resistance ofN-glycosylated enzymes produced inP. pastoris. Thus,N-glycosylation may improve pepsin resistance by enhancing the stability at acidic pH and reducing pepsin's accessibility to peptic cleavage sites. This study provides a strategy, namely, the manipulation ofN-glycosylation, for improvement of phytase properties for use in animal feed.

scholarly journals Cellular encoding of Cy dyes for single-molecule imaging

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Lilia Leisle ◽  
Rahul Chadda ◽  
John D Lueck ◽  
Daniel T Infield ◽  
Jason D Galpin ◽  
...  
Keyword(s):  
Single Molecule ◽  
Expression System ◽  
Eukaryotic Expression ◽  
Cyanine Dye ◽  
Nonsense Suppression ◽  
Xenopus Laevis Oocyte ◽  
Cellular Environment ◽  
Oocyte Expression System ◽  
Improved Technique

A general method is described for the site-specific genetic encoding of cyanine dyes as non-canonical amino acids (Cy-ncAAs) into proteins. The approach relies on an improved technique for nonsense suppression with in vitro misacylated orthogonal tRNA. The data show that Cy-ncAAs (based on Cy3 and Cy5) are tolerated by the eukaryotic ribosome in cell-free and whole-cell environments and can be incorporated into soluble and membrane proteins. In the context of the Xenopus laevis oocyte expression system, this technique yields ion channels with encoded Cy-ncAAs that are trafficked to the plasma membrane where they display robust function and distinct fluorescent signals as detected by TIRF microscopy. This is the first demonstration of an encoded cyanine dye as a ncAA in a eukaryotic expression system and opens the door for the analysis of proteins with single-molecule resolution in a cellular environment.

The melibiose/Na + symporter of Escherichia coli : kinetic and molecular properties

1990 ◽  
Vol 326 (1236) ◽  
pp. 411-423 ◽  
Keyword(s):  
Escherichia Coli ◽  
Complex Cation ◽  
Expression System ◽  
Binding Activity ◽  
Site Directed Mutagenesis ◽  
Coupling Mechanism ◽  
Facilitated Diffusion ◽  
Histidine Residues ◽  
Sugar Binding ◽  
Dependent Transport

The role of the co-transported cation in the coupling mechanism of the melibiose permease of Escherichia coli has been investigated by analysing its sugar-binding activity, facilitated diffusion reactions and energy-dependent transport reactions catalysed by the carrier functioning either as an H + , Na + or Li + -sugar symporter. The results suggest that the coupling cation not only acts as an activator for sugar-binding on the carrier but also regulates the rate of dissociation of the co-substrates in the cytoplasm by controlling the stability of the ternary complex cation-sugar—carrier facing the cell interior. Furthermore, there is some evidence that the membrane potential enhances the rate of symport activity by increasing the rate of dissociation of the co-substrates from the carrier in the cellular compartment. Identification of the melibiose permease as a membrane protein of 39 kDa by using a T7 RNA polymerase/promoter expression system is described. Site-directed mutagenesis has been used to replace individual carrier histidine residues by arginine to probe the functional contribution of each of the seven histidine residues to the symport mechanism. Only substitution of arginine for His94 greatly interferes with the carrier function. It is finally shown that mutations affecting the glutamate residue in position 361 inactivate translocation of the co-substrates but not their recognition by the permease.

scholarly journals CD4 receptor diversity in chimpanzees protects against SIV infection

2019 ◽  
Vol 116 (8) ◽  
pp. 3229-3238 ◽  
Author(s):  
Frederic Bibollet-Ruche ◽  
Ronnie M. Russell ◽  
Weimin Liu ◽  
Guillaume B. E. Stewart-Jones ◽  
Scott Sherrill-Mix ◽  
...  
Keyword(s):  
Strong Association ◽  
Glycosylation Site ◽  
Cell Entry ◽  
Site Directed Mutagenesis ◽  
Target Cells ◽  
In Silico Modeling ◽  
In The Wild ◽  
Siv Infection ◽  
Replication Fitness ◽  
Coding Variants

Human and simian immunodeficiency viruses (HIV/SIVs) use CD4 as the primary receptor to enter target cells. Here, we show that the chimpanzee CD4 is highly polymorphic, with nine coding variants present in wild populations, and that this diversity interferes with SIV envelope (Env)–CD4 interactions. Testing the replication fitness of SIVcpz strains in CD4+T cells from captive chimpanzees, we found that certain viruses were unable to infect cells from certain hosts. These differences were recapitulated in CD4 transfection assays, which revealed a strong association between CD4 genotypes and SIVcpz infection phenotypes. The most striking differences were observed for three substitutions (Q25R, Q40R, and P68T), with P68T generating a second N-linked glycosylation site (N66) in addition to an invariant N32 encoded by all chimpanzee CD4 alleles. In silico modeling and site-directed mutagenesis identified charged residues at the CD4–Env interface and clashes between CD4- and Env-encoded glycans as mechanisms of inhibition. CD4 polymorphisms also reduced Env-mediated cell entry of monkey SIVs, which was dependent on at least one D1 domain glycan. CD4 allele frequencies varied among wild chimpanzees, with high diversity in all but the western subspecies, which appeared to have undergone a selective sweep. One allele was associated with lower SIVcpz prevalence rates in the wild. These results indicate that substitutions in the D1 domain of the chimpanzee CD4 can prevent SIV cell entry. Although some SIVcpz strains have adapted to utilize these variants, CD4 diversity is maintained, protecting chimpanzees against infection with SIVcpz and other SIVs to which they are exposed.

scholarly journals Mutational Analysis of Ocriplasmin to Reduce Proteolytic and Autolytic Activity in Pichia pastoris

2020 ◽  
Vol 22 (1) ◽  
Author(s):  
Roghayyeh Baghban ◽  
Safar Farajnia ◽  
Younes Ghasemi ◽  
Reyhaneh Hoseinpoor ◽  
Azam Safary ◽  
...  
Keyword(s):  
Pichia Pastoris ◽  
Proteolytic Activity ◽  
Mutational Analysis ◽  
Expression System ◽  
Catalytic Efficiency ◽  
Site Directed Mutagenesis ◽  
Wild Type ◽  
Vitreomacular Adhesion ◽  
Autolytic Activity

Abstract Background Ocriplasmin (Jetrea) is using for the treatment of symptomatic vitreomacular adhesion. This enzyme undergoes rapid inactivation and limited activity duration as a result of its autolytic nature after injection within the eye. Moreover, the proteolytic activity can cause photoreceptor damage, which may result in visual impairment in more serious cases. Results The present research aimed to reduce the disadvantages of ocriplasmin using site-directed mutagenesis. To reduce the autolytic activity of ocriplasmin in the first variant, lysine 156 changed to glutamic acid and, in the second variant for the proteolytic activity reduction, alanine 59 mutated to threonine. The third variant contained both mutations. Expression of wild type and three mutant variants of ocriplasmin constructs were done in the Pichia pastoris expression system. The mutant variants were analyzed in silico and in vitro and compared to the wild type. The kinetic parameters of ocriplasmin variants showed both variants with K156E substitution were more resistant to autolytic degradation than wild-type. These variants also exhibited reduced Kcat and Vmax values. An increase in their Km values, leading to a decreased catalytic efficiency (the Kcat/Km ratio) of autolytic and mixed variants. Moreover, in the variant with A59T mutation, Kcat and Vmax values have reduced compared to wild type. The mix variants showed the most increase in Km value (almost 2-fold) as well as reduced enzymatic affinity to the substrate. Thus, the results indicated that combined mutations at the ocriplasmin sequence were more effective compared with single mutations. Conclusions The results indicated such variants represent valuable tools for the investigation of therapeutic strategies aiming at the non-surgical resolution of vitreomacular adhesion.

A Recombinant Soluble Form of the Integrin IIbβ3 (GPIIb-IIIa) Assumes an Active, Ligand-Binding Conformation and Is Recognized by GPIIb-IIIa–Specific Monoclonal, Allo-, Auto-, and Drug-Dependent Platelet Antibodies

Blood ◽  
1998 ◽  
Vol 92 (6) ◽  
pp. 2053-2063 ◽  
Author(s):  
Julie A. Peterson ◽  
Gian P. Visentin ◽  
Peter J. Newman ◽  
Richard H. Aster
Keyword(s):  
Ligand Binding ◽  
Expression System ◽  
Site Directed Mutagenesis ◽  
High Yield ◽  
Soluble Form ◽  
Specific Antibodies ◽  
Binding Conformation ◽  
Active Ligand ◽  
Extracellular Region ◽  
Drug Dependent

Abstract The IIb-IIIa glycoprotein complex is a favored target for allo-, auto-, and drug-dependent antibodies associated with immune thrombocytopenia. A soluble, recombinant form of the GPIIb-IIIa heterodimer that could be produced in large quantities and maintained in solution without detergent could provide a useful experimental tool for the study of platelet-reactive antibodies, but previous attempts to produce such a construct have yielded only small quantities of the end product. Using a baculovirus expression system and the dual-promoter transfer vector P2Bac, we were able to express soluble GPIIb-IIIa complex (srGPIIb-IIIa) lacking cytoplasmic and transmembrane domains in quantities of about 1,000 μg/L, about 40 times greater than reported previously. The high yield achieved may be related to inclusion of the entire extracellular region of the GPIIb light chain in the construct. srGPIIb-IIIa reacts spontaneously with fibrinogen, and this interaction is totally inhibited by the peptide RGDS. Reactions of 24 GPIIb-IIIa–specific antibodies evaluated (12 monoclonal, 3 allo-specific, 3 auto-specific, and 6 drug-dependent) with srGPIIb-IIIa were indistinguishable from reactions with platelet GPIIb-IIIa. Thus, srGPIIb-IIIa spontaneously assumes an active, ligand-binding conformation and contains epitopes for all monoclonal and human antibodies tested to date. srGPIIb-IIIa can be produced in large quantities, can readily be modified by site-directed mutagenesis, and should facilitate identification of epitopes recognized by GPIIb-IIIa–specific antibodies, study of the mechanism(s) by which certain drugs promote antibody binding to GPIIb-IIIa in drug-induced thrombocytopenia and structure-function relationships of GPIIb-IIIa. © 1998 by The American Society of Hematology.

scholarly journals FMS-like Tyrosine Kinase 3/FLT3: From Basic Science to Clinical Implications

2019 ◽  
Vol 99 (3) ◽  
pp. 1433-1466 ◽  
Author(s):  
Julhash U. Kazi ◽  
Lars Rönnstrand
Keyword(s):  
Signal Transduction ◽  
Tyrosine Kinase ◽  
Myeloid Leukemia ◽  
Current Knowledge ◽  
Biological Effects ◽  
Acquired Resistance ◽  
Cell Proliferation And Differentiation ◽  
Functional Aspects ◽  
Proliferation And Differentiation ◽  
Targeted Inhibition

FMS-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase that is expressed almost exclusively in the hematopoietic compartment. Its ligand, FLT3 ligand (FL), induces dimerization and activation of its intrinsic tyrosine kinase activity. Activation of FLT3 leads to its autophosphorylation and initiation of several signal transduction cascades. Signaling is initiated by the recruitment of signal transduction molecules to activated FLT3 through binding to specific phosphorylated tyrosine residues in the intracellular region of FLT3. Activation of FLT3 mediates cell survival, cell proliferation, and differentiation of hematopoietic progenitor cells. It acts in synergy with several other cytokines to promote its biological effects. Deregulated FLT3 activity has been implicated in several diseases, most prominently in acute myeloid leukemia where around one-third of patients carry an activating mutant of FLT3 which drives the disease and is correlated with poor prognosis. Overactivity of FLT3 has also been implicated in autoimmune diseases, such as rheumatoid arthritis. The observation that gain-of-function mutations of FLT3 can promote leukemogenesis has stimulated the development of inhibitors that target this receptor. Many of these are in clinical trials, and some have been approved for clinical use. However, problems with acquired resistance to these inhibitors are common and, furthermore, only a fraction of patients respond to these selective treatments. This review provides a summary of our current knowledge regarding structural and functional aspects of FLT3 signaling, both under normal and pathological conditions, and discusses challenges for the future regarding the use of targeted inhibition of these pathways for the treatment of patients.

scholarly journals Permissivity of Dipeptidyl Peptidase 4 Orthologs to Middle East Respiratory Syndrome Coronavirus Is Governed by Glycosylation and Other Complex Determinants

2017 ◽  
Vol 91 (19) ◽  
Author(s):  
Kayla M. Peck ◽  
Trevor Scobey ◽  
Jesica Swanstrom ◽  
Kara L. Jensen ◽  
Christina L. Burch ◽  
...  
Keyword(s):  
Middle East ◽  
Guinea Pig ◽  
Host Range ◽  
Dipeptidyl Peptidase ◽  
Glycosylation Site ◽  
Middle East Respiratory Syndrome ◽  
Virus Receptor ◽  
Dipeptidyl Peptidase 4 ◽  
Receptor Interactions ◽  
Species Specific

ABSTRACT Middle East respiratory syndrome coronavirus (MERS-CoV) utilizes dipeptidyl peptidase 4 (DPP4) as an entry receptor. While bat, camel, and human DPP4 support MERS-CoV infection, several DPP4 orthologs, including mouse, ferret, hamster, and guinea pig DPP4, do not. Previous work revealed that glycosylation of mouse DPP4 plays a role in blocking MERS-CoV infection. Here, we tested whether glycosylation also acts as a determinant of permissivity for ferret, hamster, and guinea pig DPP4. We found that, while glycosylation plays an important role in these orthologs, additional sequence and structural determinants impact their ability to act as functional receptors for MERS-CoV. These results provide insight into DPP4 species-specific differences impacting MERS-CoV host range and better inform our understanding of virus-receptor interactions associated with disease emergence and host susceptibility. IMPORTANCE MERS-CoV is a recently emerged zoonotic virus that is still circulating in the human population with an ∼35% mortality rate. With no available vaccines or therapeutics, the study of MERS-CoV pathogenesis is crucial for its control and prevention. However, in vivo studies are limited because MERS-CoV cannot infect wild-type mice due to incompatibilities between the virus spike and the mouse host cell receptor, mouse DPP4 (mDPP4). Specifically, mDPP4 has a nonconserved glycosylation site that acts as a barrier to MERS-CoV infection. Thus, one mouse model strategy has been to modify the mouse genome to remove this glycosylation site. Here, we investigated whether glycosylation acts as a barrier to infection for other nonpermissive small-animal species, namely, ferret, guinea pig, and hamster. Understanding the virus-receptor interactions for these DPP4 orthologs will help in the development of additional animal models while also revealing species-specific differences impacting MERS-CoV host range.

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