Supporting information for. Phosphatidylserine allows observation of the calcium-myristoyl switch of recoverin and its preferential binding

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1 Supporting information for Phosphatidylserine allows observation of the calcium-myristoyl switch of recoverin and its preferential binding Philippe Calvez, Thaís F. Schmidt, Line Cantin, Kristina Klinker and Christian Salesse* CUO-Recherche, Centre de recherche du CHU de Québec, Hôpital du Saint-Sacrement, Département d ophtalmologie, Faculté de Médecine, and Regroupement stratégique PROTEO, Université Laval, Québec (Québec) Canada, G1S 4L8. On leave from the Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, SP, Brazil. *Corresponding author: Phone (418) Fax (418) christian.salesse@fmed.ulaval.ca. Experimental section Materials. The deionized water used to prepare the buffer solutions was from a Barnstead Nanopure system (Barnstead, Dubuque, IA). Its resistivity and surface tension was 18.2 MΩ cm and 72 mn/m, respectively. The E. coli BL2 (DE3) plyss cells and the plasmid pet11a were from Novagen (Darmstadt, Germany). Ethylene glycol tetraacetic acid (EGTA), sodium myristate, Hepes, β mercaptoethanol and diméthylformamide (DMF) were purchased from Sigma (St Louis, MO, USA). CaCl 2 and ultrapure NaCl (99.9%) were from J.T. Baker (Phillipsburg, NJ, USA). High-grade sodium phosphates were from Merck (Darmstadt, Germany). Alexa Fluor 488 and DHPE Texas-Red were purchased from Invitrogen (Burlington, ON, USA). The resin used for protein purification was from GE healthcare (Uppsala, Sweden). 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-snglycero-3-phosphoethanolamine (DMPE), 1,2-dimyristoyl-sn-glycero-3-phosphoserine (DMPS), 1,2-dimyristoyl-snglycero-3-phosphoglycerol (DMPG), 1-palmitoyl,2-oleoyl-sn-glycero-3-phosphoinositol (POPI), 1,2-dipalmitoyl-snglycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-dioleoyl-snglycero-3-phosphoserine (DOPS), 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine (DDPC), 1,2- didocosahexaenoyl-sn-glycero-3-phosphoserine (DDPS), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2- distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) and 1,2-distearoyl-sn-glycero-3-phosphoserine (DSPS) were purchased from Avanti Polar Lipids (Alabaster, AL). Photoreceptor outer segment (POS) lipids were extracted as described previously using bovine rod outer segments purified from fresh retina obtained from a local slaughterhouse. 1 All chemicals were used as received. Expression and purification of recoverin and its mutants. The full-length bovine cdna of recoverin was ligated into the pet11a plasmid as described previously. 2 ΔCter-recoverin encoding the sequence has been amplified from wild type recoverin using primers designed to amplify this coding. The sequence has then been ligated into the pet11a plasmid. Lys 5, 11, 37 and Arg 43 have been replaced by Ser in three steps with wild type recoverin using Quickchange Lightning Site-Directed Mutagenesis (Agilent) where Lys 5 and 11 were first modified and then Lys 37 and finally Arg 43. The sequence of the mutated plasmids has been confirmed by automatic sequencing (Plateforme de séquençage et de génotypage du Centre de recherche du CHU de Québec, QC). Expression and purification of wild type recoverin and its mutants were performed as previously reported. 2 Briefly, wild type and mutants were expressed in E.coli strain BL21 (DE3) plyss containing plasmids encoding for recoverin and N-myristoyl transferase (pbb131). To allow protein N-myristoylation, sodium myristate (0,08 mm) was added 20 minutes before induction. Cells were then harvested by centrifugation and resuspended in a buffer containing 50 mm Hepes, ph 7.5, 100 mm NaCl, 5 mm β mercaptoethanol and 1 mm CaCl 2. After sonication and centrifugation, the cleared lysate was loaded to a column containing 5 ml phenyl sepharose 6 Fast flow (low sub) such as previously reported. 2 Proteins were eluted with 5 mm Hepes, ph 7.5, 100 mm NaCl, 5 mm β mercaptoethanol and 5 mm EGTA. Concentration of proteins was determined using the Bradford method, the extinction coefficient of recoverin 3 and the A 280nm /A 260nm ratio (protein concentration in mg/ml) = 1.55 * A 280nm 0.76*A 260nm 4 with similar results. The level of S1

2 myristoylation of recoverin and its mutants has been quantified by reverse phase HPLC as described previously. 2 Proteins with a level of myristoylation larger than 95 % have been used in our experiments. Surface pressure measurements. The surface pressure-area isotherms were measured using a trough from Nima- KSV at a compression speed of 16 Å 2 molecule -1 min -1 and a temperature was 23 ± 1 C. The lipids were spread using a CHCl 3 solution. For the determination of the protein binding parameters, surface pressure (Π) was measured by the Wilhelmy method using 500 µl glass troughs and the DeltaPi4 microtensiometer from Kibron Inc. (Helsinki, Finland). The experimental setup was placed in a Plexiglass box with humidity control at a temperature of 22 ± 1 C. The subphase buffer was 10 mm Hepes, ph 7.5, 1 mm CaCl 2, 5 mm β mercaptoethanol and either 100, 300 or 500 mm NaCl. In some experiments, 1 mm CaCl 2 was replaced by 5 mm EGTA. The monolayer was prepared by spreading a few microliters of a solution of phospholipids until the desired initial surface pressure (Π i ) was reached. The waiting time period for the evaporation of the spreading solvent and for the film to reach equilibrium varied with the type of lipid, the spreading volume and the initial surface pressure. 5 Then, wild type recoverin, ΔCter-recoverin or Δcharges-Nter-MRec-Ca was injected underneath the lipid monolayer until an optimal final concentration of 2 µg/ml was achieved. The kinetics of protein binding onto the phospholipid monolayer was monitored until the equilibrium surface pressure (Π e ) was reached. Determination of the binding parameters of recoverin. The maximum insertion pressure (MIP) of recoverin and its mutants was determined as described previously. 5 Briefly, recoverin is injected into the subphase underneath the phospholipid monolayer at different Π i. Then, the plot of the surface pressure increase (ΔΠ) as a function of Π i allows the determination of the MIP by extrapolating the regression of the plot to the x-axis. The synergy is obtained by adding 1 to the slope of the plot of ΔΠ as a function of Π i or more directly from the slope of the plot of Π e as a function of Π i. The uncertainty of the MIP is calculated with a confidence interval of 95% from the covariance of the experimental data on the linear regression as previously described. 6 The uncertainty on the synergy is calculated with a confidence interval of 95% as previously documented. 5 The calculation of the uncertainty of the values of MIP and synergy can also be performed using a dedicated online tool: ParametersCalculator. Ellipsometric measurements. The ellipsometric measurements were carried out with a conventional null ellipsometer using a He-Ne laser at an angle of incidence of (Brewster angle of the air-water interface for pure water is ). A circular trough made of Delrin with a diameter of 6 cm and a depth of 0.5 cm was used in these experiments. The subphase buffer contained 8 ml of 10 mm Hepes, ph 7.5, 100 mm NaCl, 5 mm β mercaptoethanol and 1 mm CaCl 2. The surface pressure was measured with a Wilhelmy Nima PS4 film balance (Coventry, England). All experiments were performed at room temperature. Protein concentration in the subphase was 2 µg/ml. Localization of MRec by epifluorescence microscopy. Phospholipid solutions contained 2 mol% Texas Red DHPE. Alexa Fluor 488 has been used to label recoverin. Briefly, the purified protein was dissolved in 0.1 M sodium bicarbonate buffer (ph 9) and the fluorescent dye was solubilized in DMF at a concentration of 5 mg/ml. An excess of dye was slowly added to the protein solution while stirring. The reaction mixture was then incubated for 2-3 h in the absence of light at room temperature with continuous stirring. The conjugate was then separated from the unreacted label by gel filtration (P-6DG, BioRad) previously equilibrated with the same buffer. To make sure the labeled protein sample was devoided of any contaminating free dye, the solution was further filtered by centrifugation at x g through a Millipore filter (5 kda) until no trace of dye was detected. The glass trough (23 cm length, 6 cm width and 0.2 cm depth) used to prepare the phospholipid monolayers was equiped with a Wilhelmy tensiometer (Kibron Inc, Helsinki, Finland). It was filled with 30 ml of buffer (10 mm Hepes (ph 7.5), 100 mm NaCl, 5 mm β-mercaptoethanol and 1 mm CaCl 2 ). After phospholipid spreading, the monolayer was compressed until the desired surface pressure was reached. Protein was then injected into the subphase to reach a final concentration of 2 µg/ml. Fluorescence was observed using an epifluorescence microscope (Eclipse TE2000-U; Nikon) equiped with a CCD camera (ORCA-ER, resolution 1344 x 1040; Hamamatsu, Bridgewater, NJ). The different fluorophores have been observed using a long-distance objective (40X) by changing the excitation filters. S2

3 Figure S1. Calcium myristoyl switch of recoverin. Cartoon model structure of myristoylated recoverin in the absence (A, pdb 1IKU) and in the presence (B, pdb1jsa) of calcium. The binding of calcium leads to the extrusion of the myristoyl group as well as of the basic residues K5, K11, K37 and R43 of recoverin, which allows its membrane binding. Table S1. Maximum insertion pressure (MIP) of myristoylated recoverin in the presence and absence of calcium upon binding to monolayers of lipids, which are typical of photoreceptor outer segment disk membranes. In the presence of calcium Phospholipid DSPC DDPC DSPS DOPS DDPS 16% PS POS MIP (mn/m) 21.6 ± ± ± ± ± ± ± 1.8 In the absence of calcium Phospholipid DSPC DDPC DSPS DOPS DDPS 16% PS POS MIP (mn/m) 22.7 ± ± ± ± ± ± ± 1.4 S3

4 Figure S2. Π-A isotherms of the DMPS monolayer in the absence and presence of 1 mm CaCl 2 as well as in the presence of both 1 mm CaCl 2 and increasing concentrations of NaCl (100, 300 and 500 mm) (the subphase also contained 10 mm Hepes at ph 7.5 and 5 mm β mercaptoethanol). Figure S3. Comparison between the MIP of myristoylated recoverin in the presence (Ca mm NaCl) and absence (EGTA mm NaCl) of calcium as well as in the presence of both calcium and 500 mm NaCl (Ca mm NaCl) upon binding onto DMPG and DMPS monolayers. S4

5 Figure S4. Comparison between the effect of calcium on the MIP of MRec-Ca relative to that of MRec-EGTA upon binding onto POPI, DMPG and DMPS monolayers, such as described in the legend to Figure 2C. The effect of calcium on the MIP of recoverin has been calculated from the following experimental data: MIP values of MRec-Ca of 26.8 ± 1.7, 24.3 ± 1.1 and 36.7 ± 2.4 mn/m have respectively been measured in the presence of POPI, DMPG and DMPS whereas MIP values of MRec-EGTA of 30.7 ± 3.2, 27.2 ± 2.6 and 24.5 ± 2.6 mn/m have been measured in the presence of POPI, DMPG and DMPS, respectively. REFERENCES (1) Demers, E.; Boisselier, E.; Horchani, H.; Blaudez, D.; Calvez, P.; Cantin, L.; Belley, N.; Champagne, S.; Desbat, B.; Salesse, C. Biochemistry 2015, 54, (2) Desmeules, P.; Penney, S.-E.; Salesse, C. Anal. Biochem. 2006, 349, (3) Pace, C. N.; Vajdos, F.; Fee, L.; Grimsley, G.; Gray, T. Protein Sci. 1995, 4, (4) Warburg, O.; Christian, W. Biochem. Z. 1941, 310, (5) Calvez, P.; Demers, E.; Boisselier, E.; Salesse, C. Langmuir 2011, 27, (6) Calvez, P.; Bussières, S.; Demers, E.; Salesse, C. Biochimie 2009, 91, S5