Purification and characterization of the agglutinins from the sponge Aaptos papillata and a study of their combining sites

The lectins from the sponge Aaptos papillata were isolated by affinity chromatography using polyleucyl blood group A + H substances from hog stomach linings as an absorbent and eluting with 3 M MgCl2. Further separation on diethylaminoethylcellulose and preparative disc electrophoresis on polyacrylamide gave the three fractions, Aaptos lectins I, II, and III. They were essentially homogenous in polyacrylamide electrophoresis and sedimentation analysis: a small second component was seen in lectins I and II in immunoelectrophoresis at high concentration. The S20,W0 values for Aaptos lectins I, II, and III were 3.5, 6.0, and 5.5. By electrophoresis in sodium dodecyl sulfate with an without beta-mercaptoethanol Aaptos lectin I showed two bands corresponding to molecular weights of 12 000 and 21 000; Aaptos lectins II and III gave only one band of molecular weight of 16 000. In isoelectric focusing, Aaptos lectin I showed bands at pH 4.7 and 5.4 and in the range between 6.8 and 7.6, while Aaptos lectins II and III were almost identical with bands at pH 3.8, 4.7 to 4.9, and 5.3. Aaptos lectin I differed from II and III in amino acid composition but the latter two were very similar. They contained no significant carbohydrate. Aaptos lectin I reacted best with blood group substances with terminal nonreducing N-acetyl-D-glucosamine residues precipitating about two-thirds of the lectin N added while blood group substances with terminal nonreducing DGalNAc were almost inactive. However, Aaptos lectin II was completely precipitated by blood group substances and glycoproteins containing terminal DGalNAc, DGlcNAc, or sialic acid residues. Aaptos lectin III had a precipitation pattern similar to Aaptos lectin II. DGlcNAc but not DGalNAc inhibited precipitation of Aaptos lectin I by blood group substances and N, N', N'', N'''-tetraacetylchitotetraose was the best inhibitor and was 2000 times more active than DGlcNAc. Precipitin reactions with Aaptos lectin II were inhibited by equal amounts of DGlcNAc and by sialic acid which were four times more potent than DGalNAc. N,N',N''-triacetylchiotriose was the best inhibitor and was 13 times better than DGlcNAc. At 37 degrees C three to four times higher amounts of inhibitor were necessary to inhibit precipitation of Aaptos lectin II than were needed at 4 degrees C, indicating higher affinity of blood group substances for Aaptos lectin II with increasing temperature. Aaptos lectin I was precipitated by the monofunctional hapten p-nitrophenyl-alphaDGalNAc, while p-nitrophenyl-betaDGalNAc did not precipitate and was a good inhibitor. Both phenomena indicate involvement of hydrophobic bonds.

Binding properties of immunoglobulin combining sites specific for terminal or nonterminal antigenic determinants in dextran

Binding constants of the dextran-reactive BALB/c mouse IgA myeloma proteins W3129 and QUPC 52 have been determined for each member of the isomaltose series of oligosaccharides and for methyl alphaDglucoside. Protein W3129 has maximum complementarity for isomaltopentaose (IM5) deltaf degrees = 7,180 cal/mol) with 55-60% of the total binding energy directed against methylalphaDglucoside. Protein QUPC 52 gives maximum binding with isomaltohexaose (IM6) (deltaF degrees = -5,340 cal/mol) and has about 70% of its total binding energy for isomaltotriose (IM3), but at most only 5% for isomaltose (IM2) or methyl alphaDglucoside. Protein W3129 precipitates with branched dextrans high in alpha (1 yields 6) linkages and reacts with but does not precipitate a synthetic alpha (1 yields 6)-linked linear dextran. Protein QUPC 52 precipitates both branched and linear dextrans. Thus, the immunodominant group for protein W3129 is mimicked by methyl alphaDglucoside and this protein reacts exclusively at the terminal nonreducing ends of alpha (1 yields 6)-linked dextran chains. Protein QUPC 52 has an immunodominant group which is expressed by IM3 but not smaller oligosaccharides and this protein can react at nonterminal locations along alpha (1 yields 6)-linked dextran chains. Precipitation of linear dextran seems to be a valid although not quantitative assay for antidextrans with nonterminal specificity. Quantitative precipitin reactions with branched and linear dextrans suggest that alpha (1 yields 6)-specific human antidextrans are mixtures of molecules having terminal and nonterminal specificities and that the fraction of each type can vary among individuals. Rabbit antisera against IM3 or IM6 coupled to bovine serum albumin also appear to contain antibodies with nonterminal specificity for dextran chains although a large fraction has terminal specificity. Low molecular weight clinical dextran N-150N (congruent to 60,000) reacted more like linear dextran than like its parent native-branched dextran B512. This is thought to result from an abundance of nonterminal determinants in clinical dextran N-150N but a very small number of functional terminal determinants per molecule. An appreciation of terminal and nonterminal specificities and of the different immunodominant structures in isomaltosyl chains has proven to be of a great value in understanding the immunochemical reactions of dextrans. Moreover, certain previous findings with fructosan-reactive mouse myeloma proteins and human antilevans (55, 84) also suggest terminal and nonterminal specificities for levan chains.

Immunochemical studies on mouse myeloma proteins reactive with dextrans or with fructosans and on human antilevans

Four BALB/c IgA mouse myeloma proteins (W3129, W3434, QUPC 52, and UPC 102) reactive with dextran, four myeloma proteins reactive with fructosans, three IgA (W3082, UPC 61, and Y5476), and one IgG2a (UPC 10), and two human antilevans were studied immunochemically. Quantitative precipitin and inhibition assays showed that W3129, W3434, and QUPC 52 had specificities for isomaltose oligosaccharides similar to those previously found with alpha(1 --> 6)-specific human antidextrans. W3129 and W3434 were most complementary to IM5 but W3129 reacted equally with IM4 and IM3 while W3434 had a greater affinity for IM4 than IM3. QUPC 52 had a larger combining region and was most complementary to IM6. Protein UPC 102 (IgA), like MOPC 104E (IgM) (27), was most complementary to the alpha(1 --> 3)-linked trisaccharide, nigerotriose, and thus differed from J558 (29), which was inhibited best by nigeropentaose. UPC 102 was similar to J558 but they differed from MOPC 104E in their reactions with non-alpha(1 --> 3)-linked disaccharides. The fructosan-specific myeloma proteins fell into two groups with different specificities. The first group, W3082 (IgA), UPC 61 (IgA), and the previously studied J606 (IgG3) (28, 29), reacted with inulin and W3082 and UPC 61 appeared to have identical specificities for beta(2 --> 1)-linked fructofuranosyl residues with maximum complementarity for the tetrasaccharide betaDfructofuranosyl (2 --> 1)betaDfructofuranosyl(2 --> 1)betaDfructofuranosyl(2 --> 6)Dglucose while protein J606 was inhibited best by the trisaccharide betaDfructofuranosyl(2 --> 1)betaDfructofuranosyl(2 --> 6)Dglucose. W3082 and UPC 61 also differed from J606 in their behavior toward sucrose and betaDfructofuranosyl(2 --> 6)Dglucose as compared with alphaDglucosyl(1 --> 3)Dfructose (turanose). The second group containing myeloma proteins UPC 10 (IgG2a) and Y5476 (IgA) behaved similarly to human antilevans in that neither reacted with inulin nor were they inhibited by the beta(2 --> 1)-linked fructose oligosaccharides. Unlike the beta(2 --> 1)-specific proteins, they reacted with perennial rye grass levan that contained over 90% beta(2 --> 6)links. The differences in specificity and site size among homogeneous mouse myeloma proteins reactive with the same antigenic determinant are completely consistent with the concept that they represent products of homogeneous clones selected from the known heterogeneous population of antibody-forming cells.