title: Calcineurin A versus NS5A-TP2/HD domain containing 2: a case study of site-directed low-frequency random mutagenesis for dissecting target specificity of peptide aptamers.
abstract: We previously identified a peptide aptamer (named R5G42) via functional selection for its capacity to slow cell proliferation. A yeast two-hybrid screen of human cDNA libraries, using R5G42 as "bait," allowed the identification of two binding proteins with very different functions: calcineurin A (CnA) (PP2B/PPP3CA), a protein phosphatase well characterized for its role in the immune response, and NS5A-TP2/HD domain containing 2, a much less studied protein induced subsequent to hepatitis C virus non-structural protein 5A expression in HepG2 hepatocellular carcinoma cells, with no known activity. Our objective in the present study was to dissect the dual target specificity of R5G42 in order to have tools with which to better characterize the actions of the peptide aptamers toward their individual targets. This was achieved through the selection of random mutants of the variable loop, derived from R5G42, evaluating their specificity toward CnA and NS5A-TP2 and analyzing their sequence. An interdisciplinary approach involving biomolecular computer simulations with integration of the sequence data and yeast two-hybrid binding phenotypes of these mutants yielded two structurally distinct conformers affording the potential molecular basis of the binding diversity of R5G42. Evaluation of the biological impact of CnA- versus NS5A-TP2-specific peptide aptamers indicated that although both contributed to the anti-proliferative effect of R5G42, CnA-binding was essential to stimulate the nuclear translocation of nuclear factor of activated T cells, indicative of the activation of endogenous CnA. By dissecting the target specificity of R5G42, we have generated novel tools with which to study each target individually. Apta-C8 is capable of directly activating CnA independent of binding to NS5A-TP2 and will be an important tool in studying the role of CnA activation in the regulation of different signaling pathways, whereas Apta-E1 will allow dissection of the function of NS5A-TP2, serving as an example of the usefulness of peptide aptamer technology for investigating signaling pathways.
authors.affiliation: Differentiation & Cell Cycle Group, Laboratoire de Biologie Moléculaire de la Cellule, UMR5239, Centre National pour la Recherche Scientifique (CNRS), Ecole Normale Supérieure de Lyon, Université Lyon 1, Lyon, France.
authors.forename: Silvia
authors.initials: S
authors.lastname: Dibenedetto
authors.forename: David
authors.initials: D
authors.lastname: Cluet
authors.forename: Pierre-Nicolas
authors.initials: PN
authors.lastname: Stebe
authors.forename: Véronique
authors.initials: V
authors.lastname: Baumle
authors.forename: Jérémie
authors.initials: J
authors.lastname: Léault
authors.forename: Raphaël
authors.initials: R
authors.lastname: Terreux
authors.forename: Marc
authors.initials: M
authors.lastname: Bickle
authors.forename: Benoit D E
authors.initials: BD
authors.lastname: Chassey
authors.forename: Ivan
authors.initials: I
authors.lastname: Mikaelian
authors.forename: Pierre
authors.initials: P
authors.lastname: Colas
authors.forename: Martin
authors.initials: M
authors.lastname: Spichty
authors.forename: Michele
authors.initials: M
authors.lastname: Zoli
authors.forename: Brian B
authors.initials: BB
authors.lastname: Rudkin
mesh_terms: D000818:Animals; D052158:Aptamers, Peptide / Q000235:genetics / Q000378:metabolism*; D019703:Calcineurin / Q000378:metabolism*; D045744:Cell Line, Tumor; D006367:HeLa Cells; D006801:Humans; D016297:Mutagenesis, Site-Directed; D051381:Rats; D020798:Two-Hybrid System Techniques; D017361:Viral Nonstructural Proteins / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase
chemical_list: D052158:Aptamers, Peptide; D019703:Calcineurin; D017361:Viral Nonstructural Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase; C525673:PPP3CA protein, human