Fructose-1-phosphate (F1P) is the preferred effector of the catabolite repressor/activator (Cra) protein of the soil bacterium Pseudomonas putida but its ability to bind other metabolic intermediates in vivo is unclear. The Cra protein of this microorganism (Cra(PP)) was submitted to mobility shift assays with target DNA sequences (the PfruB promoter) and candidate effectors fructose-1,6-bisphosphate (FBP), glucose 6-phosphate (G6P), and fructose-6-phosphate (F6P). 1 mM F1P was sufficient to release most of the Cra protein from its operators but more than 10 mM of FBP or G6P was required to free the same complex. However, isothermal titration microcalorimetry failed to expose any specific interaction between Cra(PP) and FBP or G6P. To solve this paradox, transcriptional activity of a PfruB-lacZ fusion was measured in wild-type and ΔfruB cells growing on substrates that change the intracellular concentrations of F1P and FBP. The data indicated that PfruB activity was stimulated by fructose but not by glucose or succinate. This suggested that Cra(PP) represses expression in vivo of the cognate fruBKA operon in a fashion dependent just on F1P, ruling out any other physiological effector. Molecular docking and dynamic simulations of the Cra-agonist interaction indicated that both metabolites can bind the repressor, but the breach in the relative affinity of Cra(PP) for F1P vs FBP is three orders of magnitude larger than the equivalent distance in the Escherichia coli protein. This assigns the Cra protein of P. putida the sole role of transducing the presence of fructose in the medium into a variety of direct and indirect physiological responses.

• Publication type
• Journal Article MeSH

K udržování buněčné homeostázy je nutné, aby buněčné proteiny vytvářely složité a dynamické molekulární komplexy. Proto je i vysvětlení základních fyziologických procesů na molekulární úrovni založeno na studiu protein‑proteinových interakcí. Nejdříve probíhá kvalitativní analýza proteinových komplexů. Následně jsou identifikované proteinové interakce kvantifikovány po bio­chemické stránce. Detailní informace o strukturní podstatě daných protein‑proteinových interakcí pak mohou být získány pomocí krystalografických metod. Náhled do uspořádání proteinových komplexů na molekulární úrovni umožňuje racionálně navrhovat nové syntetické látky, které cíleně ovlivňují proteinové interakce a tím i nejrůznější fyziologické nebo patologické procesy. Tato souhrnná práce je zaměřena na popis nejčastěji používaných metod pro kvalitativní i kvantitativní hodnocení proteinových interakcí. Metody koimunoprecipitace (Co‑IP) a afinitní koprecipitace je možné využít jako prvotní nástroj pro identifikaci interakčních partnerů studovaného proteinu. Detailní bio­chemická analýza mezimolekulární interakce pak vyžaduje definování kinetických a termodynamických parametrů. Pro studium afinity dvou interakčních partnerů a kinetiky reakce je možné použít metodu rezonance povrchového plazmonu (surface plasmon resonance – SPR), pro studium afinity a inhibičního potenciálu inhibitorů metodu fluo­rescenční polarizace (FP) a pro detailní popis afinity a termodynamických parametrů interakce (∆G, ∆H a ∆S) metodu izotermální titrační kalorimetrie (isothermal titration calorimetry – ITC). Výzkum proteinových interakcí na molekulární úrovni je nejen významný pro základní výzkum, ale přináší i nové metodické přístupy, které otvírají další možnosti při racionálním navrhování nových terapeutických látek.

In order to maintain cellular homeostasis, cellular proteins coexist in complex and variable molecular assemblies. Therefore, understanding of major physiological processes at molecular level is based on analysis of protein‑protein interaction networks. Firstly, composition of the molecular assembly has to be qualitatively analyzed. In the next step, quantitative bio­chemical properties of the identified protein‑protein interactions are determined. Detailed information about the protein‑protein interaction interface can be obtained by crystallographic methods. Accordingly, the insight into the molecular architecture of these protein‑protein complexes allows us to rationally design new synthetic compounds that specifically influence various physiological or pathological processes by targeted modulation of protein interactions. This review is focused on description of the most used methods applied in both qualitative and quantitative analysis of protein‑protein interactions. Co‑immunoprecipitation and affinity co‑precipitation are basic methods designed for qualitative analysis of protein binding partners. Further bio­chemical analysis of the interaction requires definition of kinetic and thermodynamic parameters. Surface plasmon resonance (SPR) is used for description of affinity and kinetic profile of the interaction, fluorescence polarization (FP) method for fast determination of inhibition potential of inhibitors and isothermal titration calorimetry (ITC) for definition of thermodynamic parameters of the interaction (∆G, ∆H and ∆S). Besides the importance of uncovering the molecular basis of protein interactions for basic research, the same methodological approaches open new possibilities in rational design of novel therapeutic agents. Key words: protein interaction networks – co‑immunoprecipitation – pull‑down analysis – surface plasmon resonance – fluorescence polarization – isothermal titration calorimetry This work was supported by the European Regional Development Fund and the State Budget of the Czech Republic (RECAMO, CZ.1.05/2.1.00/03.0101) and by MH CZ – DRO (MMCI, 00209805). The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE “uniform requirements” for biomedical papers. Submitted: 31. 1. 2014 Accepted: 10. 3. 2014

• Keywords
• koimunoprecipitace, izotermální titrační kalorimetrie, afinitní koprecipitace, pull-down analýza,
• MeSH
• Fluorescence Polarization methods   MeSH
• Immunoprecipitation methods   MeSH
• Calorimetry methods   MeSH
• Ligands MeSH
• Protein Interaction Mapping * methods   MeSH
• Protein Interaction Maps MeSH
• Surface Plasmon Resonance methods   MeSH
• Thermodynamics MeSH
• Protein Binding * MeSH
• Publication type
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH

BACKGROUND: Lectins are proteins of non-immune origin capable of binding saccharide structures with high specificity and affinity. Considering the high encoding capacity of oligosaccharides, this makes lectins important for adhesion and recognition. The present study is devoted to the PA-IIL lectin from Pseudomonas aeruginosa, an opportunistic human pathogen capable of causing lethal complications in cystic fibrosis patients. The lectin may play an important role in the process of virulence, recognizing specific saccharide structures and subsequently allowing the bacteria to adhere to the host cells. It displays high values of affinity towards monosaccharides, especially fucose--a feature caused by unusual binding mode, where two calcium ions participate in the interaction with saccharide. Investigating and understanding the nature of lectin-saccharide interactions holds a great potential of use in the field of drug design, namely the targeting and delivery of active compounds to the proper site of action. RESULTS: In vitro site-directed mutagenesis of the PA-IIL lectin yielded three single point mutants that were investigated both structurally (by X-ray crystallography) and functionally (by isothermal titration calorimetry). The mutated amino acids (22-23-24 triad) belong to the so-called specificity binding loop responsible for the monosaccharide specificity of the lectin. The mutation of the amino acids resulted in changes to the thermodynamic behaviour of the mutants and subsequently in their relative preference towards monosaccharides. Correlation of the measured data with X-ray structures provided the molecular basis for rationalizing the affinity changes. The mutations either prevent certain interactions to be formed or allow formation of new interactions--both of afore mentioned have strong effects on the saccharide preferences. CONCLUSION: Mutagenesis of amino acids forming the specificity binding loop allowed identification of one amino acid that is crucial for definition of the lectin sugar preference. Altering specificity loop amino acids causes changes in saccharide-binding preferences of lectins derived from PA-IIL, via creation or blocking possible binding interactions. This finding opens a gate towards protein engineering and subsequent protein design to refine the desired binding properties and preferences, an approach that could have strong potential for drug design.

• MeSH
• Adhesins, Bacterial genetics   chemistry   MeSH
• Chromatography, Affinity MeSH
• Financing, Organized MeSH
• Polymorphism, Single Nucleotide MeSH
• Protein Conformation MeSH
• Crystallography, X-Ray MeSH
• Lectins genetics   chemistry   MeSH
• Models, Molecular MeSH
• Monosaccharides chemistry   MeSH
• Mutagenesis, Site-Directed MeSH
• Protein Engineering MeSH
• Pseudomonas aeruginosa genetics   MeSH
• Ralstonia solanacearum chemistry   MeSH
• Recombinant Proteins genetics   isolation & purification   MeSH
• Plant Lectins chemistry   MeSH
• Amino Acid Substitution MeSH
• Binding Sites MeSH

• MeSH
• Lasers MeSH
• Publication type
• Meeting Abstract MeSH
• Collected Work MeSH

• Conspectus
• Optika
• NML Fields
• fyzika, biofyzika
• technika