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112 CHAPITRE 3. STRUCTURE DE L’HC DE C. MAENAS PAR ESI-MS gave values of 3.2 mM for the dissociation constant and 2.8 sites per hexamer (Johnson et al., 1984). For the spiny lobster Panulirus interruptus, purification of each subunit type and reassembly into homohexamers showed that the sensitivity to lactate was subunit-dependent : some homohexamers were sensitive whereas others were not (Johnson et al., 1987). However, in native hexamers as well as in sensitive reassociated homohexamers, analysis of oxygen equilibrium curves showed that there was approximately only one binding site per hexamer, evidencing that the specific site was not located on a single subunit but was formed within the quaternary structure of the protein (Johnson et al., 1987). For Homarus vulgaris, ultrafiltration and equilibrium dialysis using labelled ligands showed that there were approximately 2 molecules bound per dodecamer, which is consistent with the finding of one site per hexamer for Panulirus interruptus ; the same result was observed for urate but urate and lactate binding sites were different and independent (Nies et al., 1992). Moreover, lactate does not bind to hemocyanin in a cooperative way, suggesting that the conformational changes induced by fixation on one site does not influence the other site (Nies et al., 1992). However, a small angle X-ray scattering study (SAXS) of Homarus americanus hemocyanin along with electron microscopy showed that upon addition of 10 mM lactate the two hexamers constituting the dodecamer got closer by about 0.5 nm (Hartmann et al., 2001), thus implying that even local changes at the binding sites may have a global effect on the quaternary structure of the protein. Isothermal titration calorimetry performed on sensible and insensible hemocyanins revealed that insensible hemocyanins did not bind lactate, whereas the sensible ones did (Taylor et al., 2000). A recent study of O2-dissociation curves of Carcinus maenas hemocyanin reported the binding of 0.35 lactate ion per functional subunit, that is to say 4 sites per dodecamer or 2 sites per hexamer (Weber et al., 2008). This is different from the data from Homarus vulgaris and Panulirus interruptus but close to the results for Callinectes sapidus, a brachyuran crab like Carcinus. In this context, the precise mechanism of lactate binding, the involved amino-acids and the induced conformational changes remained to be determined. Many studies have also demonstrated the crucial role of calcium and pH for hemocyanin structure and function. Upon dialysis against EDTA to remove calcium and pH increase, complexes are dissociated and O2-binding capacity is lost (Herskovits, 1988, Molon et al., 2000, Brenowitz et al., 1983, Olianas et al., 2006). Some species show unusual stability against dissociation (Beltramini et al., 2005). Usually, reassociation occurs upon return to physiological pH values and addition of calcium. Divalent cations and pH are also known to modify hemocyanin oxygen-binding properties (Truchot, 1992, Bridges, 2001, Olianas et al., 2006, deFur et al., 1990, Andersson et al., 1982, Morimoto et Kegeles, 1971). In recent years, mass spectrometry (MS) has emerged as a new and potent tool for structural analysis of protein complexes and protein interactions with various ligands (Chausson et al., 2004, Sanglier et al., 2003, Zal et al., 2002, Bruneaux et al., 2008, Oldham et al., 2003, Robinson et al.,
3.2. MANUSCRIT : STRUCTURAL STUDY OF C. MAENAS HC BY ESI-MS 113 2007). The possibility of preserving the fragile non-covalent interactions through the electrospray ionization (ESI) process has allowed probing quaternary structures of various assemblies and following association and dissociation of non-covalent complexes and incorporation of small organic molecules or inorganic ions (Potier et al., 1997, van Duijn et al., 2006, Tahallah et al., 2002, van den Heuvel et al., 2004, Rogniaux et al., 2001, Levy et al., 2008). All these works are examples illustrating the structural studies made possible by ESI-MS ; numerous works have successfully used the ESI source since its development. In this context, it was interesting to attempt using an ESI-MS approach to study the interaction between L-lactate and Carcinus maenas hemocyanin and the effect of divalent cations on its structure. C. maenas hemocyanin is the major protein found in the hemolymph of the crab and occurs mainly as dodecamers and to a lesser extent as hexamers. pH, lactate and divalent cations are known to have an effect on its properties (Truchot, 1980, 1975). Its constituting subunits were characterized by ESI-MS in denaturing conditions and the complexes by ESI-MS in native conditions, as described in the study by Sanglier and collaborators (Sanglier et al., 2003). In this paper, we expose an attempt to dissociate the subunits at alkaline pH and to probe their potential association with L-lactate in non-covalent conditions. An investigation of the influence of divalent cations on the reassociation of subunits was also performed using EDTA. 3.2.2 Experimental procedures Animal collection and hemocyanin sampling and purification Carcinus maenas individuals were caught by baited traps in the intertidal zone in Roscoff, France, and kept in running sea water at ambient temperature (salinity 35-35.4 , temperature 15-17.5°C). Hemolymph was withdrawn with a syringe through the articular membrane of a walking leg and immediately put on ice. Samples were centrifugated for 10 min at 10000 g to pellet cells and coagulated proteins. For whole hemolymph study, the supernatant was recovered and frozen at -20°C. For purified complexes study, dodecamers and hexamers were separated by size-exclusion chromatography (SEC) using a Superose-6 10/300 GL column (Amersham Bioscience) at an elution rate of 0.25 ml/min with a crustacean physiological saline buffer (500 mM NaCl, 10 mM KCl, 30 mM MgSO4, 20 mM CaCl2, 50 mM Tris, pH 7.8, modified from (Chausson et al., 2004)). Collected fractions purity was assessed with the same system. Purified samples were frozen at -20°C. For preliminary analyses of hemocyanin in denaturing and non-covalent conditions, samples were withdrawn from several individuals kept in running sea water under several salinity and oxygenation conditions. For all dissociation and association experiments using triethanolamine (TEA), formic acid (FA), L-lactic acid and EDTA, the whole-hemolymph samples were issued from the same individual
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THESE DE DOCTORAT DE L’UNIVERSITE
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i Résumé / Abstract Réponse adap
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iv SOMMAIRE 4.2 Objectifs de l’é
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2 CHAPITRE 1. INTRODUCTION Les éco
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4 CHAPITRE 1. INTRODUCTION 1.1 Mili
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6 CHAPITRE 1. INTRODUCTION Les prin
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8 CHAPITRE 1. INTRODUCTION TAB. 1.1
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10 CHAPITRE 1. INTRODUCTION et cycl
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FIG. 1.5 - Localisation des princip
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(a) FIG. 1.6 - Fonctionnement d’u
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16 CHAPITRE 1. INTRODUCTION TAB. 1.
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18 CHAPITRE 1. INTRODUCTION FIG. 1.
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24 CHAPITRE 1. INTRODUCTION le mili
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26 CHAPITRE 1. INTRODUCTION Capacit
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28 CHAPITRE 1. INTRODUCTION TAB. 1.
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30 CHAPITRE 1. INTRODUCTION 700 600
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32 CHAPITRE 1. INTRODUCTION férent
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34 CHAPITRE 1. INTRODUCTION (a) (b)
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40 CHAPITRE 1. INTRODUCTION 1 P 50
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42 CHAPITRE 1. INTRODUCTION presque
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44 CHAPITRE 1. INTRODUCTION affecte
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50 CHAPITRE 1. INTRODUCTION fure co
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52 CHAPITRE 1. INTRODUCTION amélio
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54 CHAPITRE 1. INTRODUCTION 1.5 Que
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56 CHAPITRE 2. ESI-MS ET MALLS APPL
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162 CHAPITRE 4. PLASTICITÉ PHÉNOT
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Dénaturant Natif
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172 CHAPITRE 5. ADAPTATIONS RESPIRA
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216 CHAPITRE 6. CONCLUSION ET PERSP
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Annexe A Détermination des masses
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229 10000 h280 .M h) h280−h337 80
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Annexe B Détermination des distrib
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233 Modèle 2 : 2 sous-unités lég
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235 1 0.9 0.8 6 s-u aléatoires 2 s
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Bibliographie Adair, G. S. The hemo
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BIBLIOGRAPHIE 239 Catalina, M. I.,
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BIBLIOGRAPHIE 241 Farmer, C. S., J.
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BIBLIOGRAPHIE 243 Hourdez, S. Adapt
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BIBLIOGRAPHIE 245 Mangum, C. P. Sub
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BIBLIOGRAPHIE 247 Rainer, J., C. P.
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BIBLIOGRAPHIE 249 Svedberg, T. et I
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BIBLIOGRAPHIE 251 Vanin, S., E. Neg
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Liste des figures 1.1 Cycle des mar
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LISTE DES FIGURES 255 4.17 Profils
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Table des matières Résumé Sommai
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TABLE DES MATIÈRES 261 4.3.5 Spect
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TABLE DES MATIÈRES 263 Table des m
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