Binding between immobilized anti-colipase purified antibodies and colipase. Radioimmunoassay of colipase from pig plasma and pancreatic juice

Lipid binding and activating properties of porcine pancreatic colipase split at the Ile79-Thr80 bond

Porcine colipase, the protein cofactor of pancreatic lipase, was isolated from pancreas freshly collected on animals and from a side fraction from the production of insulin (Novo Nordisk A/S). Samples of purified colipase were analyzed for homogeneity by polyacrylamide gel electrophoresis, reverse-phase high-performance liquid chromatography (RPLC), quantitative N-terminal sequence determination and mass spectrometry. The activating properties of colipase preparations were assayed against tributyrin, triolein or the commercial Intralipid emulsion, in presence of bile salt. Two fractions of colipase with the same specific activity were purified from fresh pancreas. The major fraction (85%) contained one single protein corresponding to fragment 1-93 of the 95-residue form of colipase (procolipase) previously characterized in porcine pancreatic juice. The other fraction (15%) corresponded to fragment 1-91 of procolipase. Also, two fractions of colipase were purified from the side fraction supplied by Novo. These fractions consisted of the 95-residue proform of colipase and of fragment 1-93, respectively, both specifically cleaved at the Ile79-Thr80 peptide bond with partial removal of isoleucine at position 79 and serine at position 78. Procolipase split at the 79-80 bond retained full activity on tributyrin and triolein and on the Intralipid emulsion but the kinetics of hydrolysis of triacylglycerol substrates showed much longer lag periods than those observed with native procolipase. Also, all forms of procolipase split at the 79-80 bond showed one peak in RPLC but their retention time was markedly decreased as compared to that of native procolipase which indicated a weaker hydrophobic binding capacity. The value of the retention time was of the same order of magnitude as that of inactive reduced procolipase. Treatment of native procolipase by pancreatic endopeptidases showed that elastase is likely responsible for specific cleavage at the 79-80 bond of procolipase purified from the Novo extract. Limited proteolysis by trypsin of the proforms of colipase split at the 79-80 bond reduced the lag period. Results presented in this communication provide the first direct evidence showing that the finger-shaped peptide segment between half-cystine residues at positions 69 and 87 is involved in colipase-lipid interaction as previously hypothesized from the three-dimensional structure of the protein.

Bimodal action of fatty acids on PMA-stimulated O2.- production in human adherent monocytes

Not only unsaturated linear fatty acids, but also saturated monomethyl-branched fatty acids (MMBFAs), are provided by food. They are capable of penetrating into the membrane lipids and promoting lipid disorder. Both NADPH oxidase and protein kinase C (PKC) are bound to cell cytoplasmic membranes and are responsive to unesterified fatty acids (UEFAs). We found that the O2.- NADPH oxidase-mediated production of human adherent monocytes was modified by unsaturated linear and saturated branched UEFAs only in the presence of phorbol myristate acetate. This result together with our inhibition data indicated an action strictly linked to PKC activity. The type and intensity of action depended on the UEFA concentrations and chain structure. Nanomolar concentrations showed potentiating effects whereas micromolar (< CMC) concentrations displayed depressant influences MMBFAs were generally more active than the other FAs. With respect to the micromolar depressant effect, oleate and linoleate were as active and docosahexaenoate nearly as active as MMBFAs. As assessed by iso-15:0 or arachidonate action, such bimodal alteration did not occur in non-adherent monocytes and neutrophils. Certain UEFAs could be considered as 'cellular' anti-oxidants on the sites of adherent-monocyte recruitment.

Immobilized colipase affinities for lipases B, A, C and their terminal peptide (336-449): the lipase recognition site lysine residues are located in the C-terminal region

Zonal high-performance affinity chromatography has been used in order to study the interactions between pig isolipases A, B and C and the terminal peptide chain fragment 336-449 of the pig lipase on the one hand, and the homolog colipase bound to the inert LiChrosorb diol support on the other. A mathematical treatment led the to assessment of the dissociation constant of the lipase-colipase complex using isolipases or the terminal peptide as eluted acceptors and colipase as silica-bound ligand (Mahé, N., Léger, C.L., Linard, A. and Alessandri, J.-M. (1987) J. Chromatogr. 395, 511-521). A higher affinity of isolipase B as compared to isolipases A and C towards colipase was observed (KD, respectively, of 0.68, 11 and 12 microM) at pH 6.5. Under the same chromatographic conditions, the terminal peptide chain interacted with the bound colipase (KD 0.70 microM, close to that of isolipase B). The chromatographic behaviors of both native and chemically modified lipase and terminal peptide were very similar. In particular, guanidination of lysine residues of both peptide and isolipase B led to the loss of interactions with colipase. The same result was observed with the peptide preincubated in the presence of increasing amounts of free colipase. Accordingly, it is suggested that, firstly, a preferential association of isolipase B to colipase could take place and, secondly, the colipase recognition site of lipase could be located in the C-terminal region, the conformational structure of the terminal peptide not being affected by the enzymic cleavage and, therefore, being largely independent of the rest of the polypeptide molecule. On the other hand, a lower colipase affinity for isolipases A or C than for isolipase B or the C-terminal peptide could tentatively be attributed to a non-local (distant) disturbing effect of the negatively charged glycan chain, as sialic acid is present in both isoforms A and C. Finally, the present paper confirms and extends earlier studies on lipase-colipase interactions.

Double-sandwich enzyme-linked immunosorbent assay for determination of Escherichia coli heat-labile porcine enterotoxins

A "double-sandwich" ELISA for the detection and measurement of a heat-labile enterotoxin produced by porcine enterotoxigenic strains of Escherichia coli (LTp) is described. In contrast with other heat-labile toxins, LTp did not bind to agarose gels and exhibited a very low affinity for GM1 in the classical GM1-ELISA technique. The similarity of LTp with cholera toxin was confirmed by immunoblotting. This property allowed the binding of LTp to rabbit IgG anti-cholera toxin antibodies (covalently linked to polystyrene plates) and sheep anti-cholera toxin serum. The immunocomplex was revealed by anti-sheep immunoglobulin antibodies conjugated with peroxidase. Application of the "double-sandwich" ELISA to the quantitation of toxin production by two strains, which differ only in the presence or the absence of the K88ab antigen, showed that the Ent+, K88+ strain produced significantly less toxin than the Ent+, K88- derivative.

Zonal high-performance affinity chromatography as a tool for protein interaction studies with special reference to the lipase-colipase complex

The technique of zonal high-performance affinity chromatography applied to the lipase-colipase system (lipase B as eluted acceptor and colipase as silica-bonded ligand) gave qualitatively the same results as conventional affinity chromatography. The elution volume of the acceptor increases with decreasing load introduced at constant volume into the column of ligand-bonded silica. This led to the use of a mathematical treatment for calculating the dissociation constant (KD) of the lipase-colipase complex. The influence of some physical and chemical chromatographic parameters was studied. Increasing temperature and flow-rate reduced the affinity of lipase for colipase, whereas it was only slightly modified by increasing the ionic strength. The KD value was minimal and equal to 0.1 X 10(-6) M at pH 4.7 and 0.38 X 10(-6) M at pH 6.5, after correction for the flow-rate. The latter value is similar to that obtained by more conventional techniques. The absence of some marked KD modifications by ionic strength and the value of delta S for the complex association obtained by temperature studies suggest the intervention of mixed hydrophobic-ionic interactions in the formation of the lipase-colipase complex. Their respective importances are discussed.

Production and characterization of four monoclonal antibodies against porcine pancreatic colipase

Four monoclonal antibodies directed against porcine colipase have been generated by hybridization of myeloma cells with spleen cells of BALB/c immunized mice. Antibodies were screened by binding to immobilized colipase in a solid-phase assay. Monoclonal antibodies were purified by affinity chromatography on colipase coupled to Sepharose. All monoclonal antibodies are of the IgG1 class with high affinity for the antigen. The dissociation constant of the complex formed in solution between porcine colipase and antibody varied from 1.1 X 10(-10) M to 1.8 X 10(-8) M. Epitope specificity was studied for each antibody and in pairs with an enzyme-linked immunosorbent assay (ELISA). Results indicate that the four monoclonal antibodies react with at least three different antigenic regions of colipase. Finally, three monoclonal antibodies were found to be potent inhibitors of colipase activity. Antiporcine monoclonal antibodies appear to be suitable probes for studying the lipid affinity site of the protein cofactor of pancreatic lipase.

Inhibition of pancreatic colipase by antibodies and Fab fragments. Selective effects of two fractions of antibodies on the functional sites of the cofactor

Rabbit antiserum was raised against porcine pancreatic colipase and Fab fragments were prepared by papain digestion of purified antibodies followed by purification on protein A-Sepharose. Fab fragments showed inactivation toward porcine colipase activity similar to that of antiserum and purified antibodies. From inactivation studies carried out by incubating porcine colipase and lipase with Fab fragments in the absence of lipid or in the presence of triolein and sodium deoxycholate, it could be concluded that polyclonal antiporcine colipase antibodies contain fractions that bind specifically to epitopes at or near the functional regions of the porcine cofactor. Studies with an enzyme-linked immunosorbent assay showed that cross-reactivity of horse or chicken colipase with antiporcine colipase antiserum was lower than that of the human or porcine protein. Results of immunoactivation kinetic studies performed with the same proteins, fully confirmed these observations. Partial cross-reactivity between porcine and chicken colipases allowed us to fractionate antibodies by immunoaffinity chromatography on immobilized chicken colipase. Fraction I contains antibodies absorbed on porcine colipase not accessible when the cofactor is bound to lipid. Antibodies of fraction II, nonadsorbed on chicken colipase, inactivate porcine colipase preincubated with triolein/deoxycholate. Lipase had a protective effect against inactivation. Antibodies of fraction II bind likely to epitopes close to the specific region of colipase interacting with lipase. Our conclusions are in good agreement with analysis of the sequence of porcine, equine and human colipases by calculating local hydrophilicity indices.

Further results on lipase-colipase interactions studied by affinity chromatography

Affinity chromatography of lipase on a colipase-coupled gel was studied in the present paper. The elution volume of the associable lipase increased when the loaded amount decreased. A KD value of 1.9 X 10(-6) M at pH 6.2 was thus deduced. A minimum value of 1.5 X 10(-6) M was obtained at pH 5.1-5.3. Mixed micelles associated with coupled colipase, but no modifications of lipase-colipase interactions took place when mixed micelles were added to the elution buffer. DMMA-modified coupled colipase failed to interact with lipase, owing to the specific orientation of the modified cofactor in the gel.

Immunoreactive pancreatic colipase, lipase and phospholipase A2 in human plasma and urine from healthy individuals

A radioimmunoassay for each of the human pancreatic proteins (colipase, lipase and phospholipase A2) is described. Determinations of the mean concentration of each protein in plasma and urine from healthy individuals were carried out with the radioimmunoassays. The values obtained in plasma were 0.5 nM (5.3 micrograms/l), 0.6 nM (32 micrograms/l) and 0.3 nM (4.3 micrograms/l) for colipase, lipase and phospholipase A2, respectively. In urine, the corresponding values were found to be 0.2 nM (2.4 micrograms/l), 0.09 nM (4.4 micrograms/l) and less than 0.017 nM (0.2 micrograms/l). No physical interaction between any of the three proteins and the lipid particles of plasma was demonstrated by centrifugation experiments or gel filtration. Gel filtration of plasma depleted of fat by centrifugation showed the proteins only in their monomeric form. The corresponding porcine proteins displayed a binding to antibodies against the human proteins, but with a lower affinity than the homologous interactions. The binding was weak but could differentiate between the porcine proforms and activated ones, i.e., procolipase and colipase87.