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Biomedical subjects

C Ghélis

Publications and source records attributed to C Ghélis.

6 recordsLinked to original sources
PubMed1998

Conformational dynamics and enzyme activity.

Conformational flexibility and structural fluctuations play an important role in enzyme activity. A great variety of internal motions ranging over different time scales and of different amplitudes are involved in the catalytic cycle. These different types of motions and their functional consequences are considered in the light of experimental data and theoretical analyses. The conformational changes upon substrate binding, and particularly the hinge-bending motion which occurs in enzymes made of two domains, are analyzed from several well documented examples. The conformational events accompanying the different steps of the catalytic cycle are discussed. The last section concerns the motions involved in the allosteric transition which regulates the enzyme activity.

Allosteric Regulation↗
PubMed1991

Conformational stability of the covalent complex between elastase and alpha 1-proteinase inhibitor.

The equilibrium unfolding-refolding process of the elastase-alpha 1-proteinase inhibitor complex, induced by guanidinium chloride, was followed by spectroscopic methods. A reversible transition with a midpoint at 2.04 +/- 0.04 M guanidinium chloride was observed by fluorescence. This transition was attributed to elastase on the basis of circular dichroism and uv absorption difference data obtained for the covalent complex and for the free proteins. The conformational stability of elastase in the complex was analyzed considering the approximation of a two-state transition. The free energy of denaturation delta GH2O was 4.2 kcal.mol-1 for complexed elastase compared to 10.5 kcal.mol-1 for the free enzyme. Such a decrease in the stability of elastase suggests that, after forming the covalent complex with the inhibitor, the enzyme undergoes not only the expected local modifications of the active site, but also an extensive structural reorganization.

Circular Dichroism↗
PubMed1990

Conformational changes in intact and papain-modified alpha 1-proteinase inhibitor induced by guanidinium chloride.

Equilibrium unfolding-refolding processes of active and proteolytically modified alpha 1-proteinase inhibitor induced by guanidinium chloride were studied. Spectroscopic methods of ultraviolet absorption, fluorescence emission and circular dichroism were used. The functional inhibitor unfolds following a multistate process: a first transition (midpoint at 0.6 M guanidinium chloride) was observed whatever the method used and was attributed to a limited conformational modification of the region including the two tryptophan residues. At higher denaturant concentrations, two other transitions were observed, one in fluorescence (midpoint at 1.7 M guanidinium chloride), attributed to the unfolding of the polypeptide chain in the same region and the other one, observed in circular dichroism and in ultraviolet absorption (midpoint at 2.3 M guanidinium chloride), leading to the totally unfolded protein. Evidence for several intermediates was also obtained with the proteolytically modified inhibitor. If total unfolding is considered, the modified inhibitor was found to be more stable towards the denaturant than the functional form (obtained at 5.5 M and 3.5 M guanidinium chloride, respectively). The unfolding irreversibility observed was attributed to the C-terminal fragment Ser359-Lys394 associated with the main chain of the cleaved inhibitor.

Circular Dichroism↗
PubMed1980

Transient conformational states in proteins followed by differential labeling.

Refolding of previously denatured and reduced elastase has been followed by titration of chemical reactivities of amino acid side chains to study the topography of the protein in the native state, and the microenvironment variations of protein side chains during the structural transition. Groups accessible to chemical reagents in the denatured form and buried in the "native" form were used as a local conformational probe. Times of labeling, depending on the reagent used, ranged from 100 to 800 ms. The reaction was stopped by isotopic dilution with an excess of unlabeled reagent under denaturing conditions to obtain a chemically homogeneous but heterogeneously labeled material. Peptide fractionation after degradation of the labeled proteins allowed the determination of the amount of radioactive label incorporated by the individual side chains during the refolding. Refolding rates, determined by physicochemical, enzymatic or immunochemical criteria, were compared with the conformational states of protein areas and evaluated by the variation of chemical reactivity at various denaturant concentrations. The importance of the last folding stages is emphasized by the results obtained which indicate that early during the refolding, two domain substructures (H-40 to H-71 and M-180 to H-200)( are stabilized, while the protein remains inactive at the time ranges of the labeling reactions.

Acetic Anhydrides↗
PubMed1979

[Conformational coupling between structural units. A decisive step in the functional structure formation].

Proteins built up of several structural domains are compared with oligomeric proteins made up of several subunits. On this basis the functional consequences of a conformational coupling between domains are analyzed. From the data obtained on the elastase molecule it is proposed that the last step in protein folding insures the optimal coupling between domains and the energy of interaction is utilized for catalysis.

Catalysis↗