Orientation of Bound Ligands in Mannose-binding Proteins

Mannose-binding proteins (MBPs) are C-type animal lectins that recognize high mannose oligosaccharides on pathogenic cell surfaces. MBPs bind to their carbohydrate ligands by forming a series of Ca2+ coordination and hydrogen bonds with two hydroxyl groups equivalent to the 3- and 4-OH of mannose. In this work, the determinants of the orientation of sugars bound to rat serum and liver MBPs (MBP-A and MBP-C) have been systematically investigated. The crystal structures of MBP-A soaked with monosaccharides and disaccharides and also the structure of the MBP-A trimer cross-linked by a high mannose asparaginyl oligosaccharide reveal that monosaccharides or α1–6-linked mannose bind to MBP-A in one orientation, whereas α1–2- or α1–3-linked mannose binds in an orientation rotated 180° around a local symmetry axis relating the 3- and 4-OH groups. In contrast, a similar set of ligands all bind to MBP-C in a single orientation. The mutation of MBP-A His189 to its MBP-C equivalent, valine, causes Manα1–3Man to bind in a mixture of orientations. These data combined with modeling indicate that the residue at this position influences the orientation of bound ligands in MBP. We propose that the control of binding orientation can influence the recognition of multivalent ligands. A lateral association of trimers in the cross-linked crystals may reflect interactions within higher oligomers of MBP-A that are stabilized by multivalent ligands. Mannose-binding proteins (MBPs) are C-type animal lectins that recognize high mannose oligosaccharides on pathogenic cell surfaces. MBPs bind to their carbohydrate ligands by forming a series of Ca2+ coordination and hydrogen bonds with two hydroxyl groups equivalent to the 3- and 4-OH of mannose. In this work, the determinants of the orientation of sugars bound to rat serum and liver MBPs (MBP-A and MBP-C) have been systematically investigated. The crystal structures of MBP-A soaked with monosaccharides and disaccharides and also the structure of the MBP-A trimer cross-linked by a high mannose asparaginyl oligosaccharide reveal that monosaccharides or α1–6-linked mannose bind to MBP-A in one orientation, whereas α1–2- or α1–3-linked mannose binds in an orientation rotated 180° around a local symmetry axis relating the 3- and 4-OH groups. In contrast, a similar set of ligands all bind to MBP-C in a single orientation. The mutation of MBP-A His189 to its MBP-C equivalent, valine, causes Manα1–3Man to bind in a mixture of orientations. These data combined with modeling indicate that the residue at this position influences the orientation of bound ligands in MBP. We propose that the control of binding orientation can influence the recognition of multivalent ligands. A lateral association of trimers in the cross-linked crystals may reflect interactions within higher oligomers of MBP-A that are stabilized by multivalent ligands. mannose-binding protein carbohydrate-recognition domain noncrystallographic symmetry 2,4-methylpentanediol crystallography NMR system High mannose structures present on cell surfaces represent important recognition elements in the immune response. Serum mannose-binding proteins (MBPs)1 are C-type lectins that function in immune surveillance by recognizing high mannose structures present on pathogenic organisms such as bacteria and fungi (1Weis W.I. Taylor M.E. Drickamer K. Immunol. Rev. 1998; 163: 19-34Crossref PubMed Scopus (892) Google Scholar). MBPs trigger cell killing by activating the complement pathway, leading to opsonization or direct lysis of the target cell (2Ikeda K. Sannoh T. Kawasaki N. Kawasaki T. Yamashina I. J. Biol. Chem. 1987; 262: 7451-7454Abstract Full Text PDF PubMed Google Scholar, 3Kuhlman M. Joiner K. Ezekowitz R.A.B. J. Exp. Med. 1989; 169: 1733-1745Crossref PubMed Scopus (388) Google Scholar, 4Super M. Levinsky R.J. Turner M.W. Clin. Exp. Immunol. 1990; 79: 144-150Crossref PubMed Scopus (77) Google Scholar, 5Tenner A.J. Robinson S.L. Ezekowitz R.A. Immunity. 1995; 3: 485-493Abstract Full Text PDF PubMed Scopus (151) Google Scholar). The ability of these proteins to distinguish foreign from self through the recognition of unique carbohydrate structures thereby contributes to host defense independent of an antibody response. Rodents and some other mammals (6Mogues T. Ota T. Tauber A.I. Sastry K.N. Glycobiology. 1996; 6: 543-550Crossref PubMed Scopus (59) Google Scholar) express two related MBPs in the serum and the liver in which the rat are designated MBP-A and MBP-C, respectively (7Drickamer K. Dordal M.S. Reynolds L. J. Biol. Chem. 1986; 261: 6878-6886Abstract Full Text PDF PubMed Google Scholar). Both proteins can fix complement, although the biological role of the liver-associated MBP is unclear at present. Each MBP consists of a cysteine-rich N-terminal domain followed by a collagenous region, an α-helical “neck” and a C-terminal carbohydrate recognition domain (CRD) (7Drickamer K. Dordal M.S. Reynolds L. J. Biol. Chem. 1986; 261: 6878-6886Abstract Full Text PDF PubMed Google Scholar). The CRD mediates recognition of target cells, and the collagenous domain interacts with MBP-associated serine proteases that trigger the downstream complement response (8Wallis R. Drickamer K. J. Biol. Chem. 1999; 274: 3580-3589Abstract Full Text Full Text PDF PubMed Scopus (97) Google Scholar). MBP polypeptides are assembled into trimeric building blocks that contain collagenous triple helices. Trimer formation requires the presence of the neck region, which associates into an α-helical coiled-coil structure (9Sheriff S. Chang C.Y. Ezekowitz R.A.B. Nat. Struct. Biol. 1994; 1: 789-794Crossref PubMed Scopus (212) Google Scholar, 10Weis W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar). Disulfide bonds formed between cysteine-rich domains of MBP-A mediate higher order oligomerization of the trimeric building block, a property associated with more efficient complement fixation (8Wallis R. Drickamer K. J. Biol. Chem. 1999; 274: 3580-3589Abstract Full Text Full Text PDF PubMed Scopus (97) Google Scholar, 11Wallis R. Drickamer K. Biochem. J. 1997; 325: 391-400Crossref PubMed Scopus (54) Google Scholar). MBPs have a broad carbohydrate specificity concordant with their need to recognize a variety of pathogenic cell surfaces. This specificity includes d-mannose,N-acetyl-d-glucosamine, and l-fucose (12Lee R.T. Ichikawa Y. Fay M. Drickamer K. Shao M.-C. Lee Y.C. J. Biol. Chem. 1991; 266: 4810-4815Abstract Full Text PDF PubMed Google Scholar). The common feature of these sugars is the presence of vicinal equatorial hydroxyl groups in the stereochemistry of the 3- and 4-OH groups of d-mannose, and these sugars are referred to herein as “Man-type” ligands. The structural basis of MBP carbohydrate specificity has been investigated by high resolution x-ray crystallographic analysis of rat MBP-A (13Weis W.I. Drickamer K. Hendrickson W.A. Nature. 1992; 360: 127-134Crossref PubMed Scopus (852) Google Scholar) and MBP-C (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). The MBP CRD structure consists of a compactly folded domain that contains a series of loops stabilized by two Ca2+. Carbohydrate binding occurs through direct coordination of one of the Ca2+, which is designated the principal Ca2+, and hydrogen bond interactions with side chains of amino acids that also serve as ligands for this Ca2+, thereby forming an intimately linked ternary complex of protein Ca2+ and sugar (Fig. 1). Similar to most lectins, MBPs display only weak affinity for monovalent sugar ligands, with dissociation constants Kd in the (12Lee R.T. Ichikawa Y. Fay M. Drickamer K. Shao M.-C. Lee Y.C. J. Biol. Chem. 1991; 266: 4810-4815Abstract Full Text PDF PubMed Google Scholar, Weis W.I. R.A. Drickamer K. J. Biol. Chem. 1994; Full Text PDF PubMed Google bind to target cell surfaces. This property between foreign and host cells, of which display ligands on their surfaces. The trimeric structures of of rat and MBPs the CRD α-helical neck reveal that the sugar binding on the trimer are to bind to of high mannose oligosaccharides (9Sheriff S. Chang C.Y. Ezekowitz R.A.B. Nat. Struct. Biol. 1994; 1: 789-794Crossref PubMed Scopus (212) Google Scholar, 10Weis W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar). are to bind to the of ligands present on and cell surfaces. The of MBP-A and MBP-C amino and x-ray analysis has that have similar structures (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). The also similar specificity for ligands, in their for MBP-C binds to the structures of whereas MBP-A binds to sugars of oligosaccharide chains R.A. T. Drickamer K. M.S. J. Biol. Chem. 1990; Full Text PDF PubMed Google Scholar). Lee and R.T. Lee Y.C. J. 1997; PubMed Scopus Google Scholar, M.S. Lee R.T. Lee Y.C. 1997; PubMed Scopus Google Scholar) have that the R.T. Lee Y.C. J. 1997; PubMed Scopus Google Scholar) and a M.S. Lee R.T. Lee Y.C. 1997; PubMed Scopus Google Scholar) bind with higher affinity to MBP-C monosaccharides or other whereas MBP-A such The structural basis for these has been from the crystal structures of MBP which are MBP-A bound to an asparaginyl oligosaccharide (13Weis W.I. Drickamer K. Hendrickson W.A. Nature. 1992; 360: 127-134Crossref PubMed Scopus (852) Google Scholar) and MBP-C bound to a series of monosaccharides (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). The in the of sugar binding by MBP-A and MBP-C in these structures is that the orientation of the sugar is in the two (Fig. 1). this is related to the specificity of these two have high resolution crystal structures of MBP-A and MBP-C bound to carbohydrate ligands. The indicate that a single residue in the binding can influence the of which is to on the ability of the protein to with We also the structure of trimeric MBP-A cross-linked by an oligosaccharide and the of this structure for multivalent cell recognition and complement The of and and also and from and from and the from Lee A trimeric of designated W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google and a of MBP-C (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar) and as The His189 of MBP-A by with in the W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar). The of the MBP-A to at The His189 of MBP-A by from the two The proteins and as for the of the and MBP-A trimer and MBP-C at by MBP-A crystals by of MBP-A in and with of or and data crystals into 2,4-methylpentanediol by into of the and and at ligands in two at the in I. MBP-C crystals by of protein in and with and The crystals into by into of the and and at for data ligands in the two at the in The crystals in a for data and for MBP-A trimer soaked with and from and structure and structure for the and and structure and structure for the and most in in the The is with cell with one trimer in the in are for and from and structure and structure for the and in R.A. M.W. J. Google Scholar). in a and for MBP-C trimer soaked with most affinity in the is in the The is with cell constants a with one in the in are for R.T. Lee Y.C. J. 1997; PubMed Scopus Google M.S. Lee R.T. Lee Y.C. 1997; PubMed Scopus Google Scholar). in a The in the The is with cell with one trimer in the in are for The in the is in the The is with cell constants a with one in the in are for on an on a x-ray at between and 180° of data with of MBP-C, of data with of and with and 1997; PubMed Scopus Google Scholar). are in and In all the crystals to the MBP-A W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar) or MBP-C (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar) structures to direct by and other as the side Ca2+ and the in the in crystallography NMR system J. M. R.J. T. 1998; PubMed Scopus Google Scholar). a of the data as the set for the of the Nature. 1992; PubMed Scopus Google Scholar). The structures (MBP-A trimer or MBP-C as a single and the as at The resolution to of of the to in of resolution and of and S. Hendrickson W.A. 1987; Scopus Google Scholar) and J. Biol. 1994; PubMed Scopus Google Scholar) the structures of and The common to the structures to a common set that to structures for for of these the and other to and the structures to are in and at to crystals of the MBP-A A of in and with an of and The oligosaccharide for the of the and to the of protein to in two and with The for structure A single crystal of to a the for and in a on an on a at and with a The and the A between the crystal and The The data with and The cell is a and The and on a the data that the is in in the The data set a of and with an of The data are on the protein of the have between and A function a noncrystallographic symmetry axis from the axis and from the a and to the The structure by the MBP-A trimer W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar) with Ca2+, and as a Scholar). A function data in the resolution of and a of of the that higher other of the the the 1990; Scopus Google Scholar) of the function in two for the trimer as a and the as The most from the function as such this The into two groups of the are related by the and the two groups are related by the that the contains two trimers on the two trimers one the one the trimer with to the in a the axis for the of This a single The two trimers as and as data from and data from The at the of this The trimers are to a cell the trimer are of the the is its of the structure in and The trimers and that in the of most of the into the The amino sugar the sugars are in one of the in the the mannose are and Ca2+. The and are and The bond and from and A of of the amino acids are in the most of the R.A. M.W. J. Google and are in The structure of the MBP-A CRD with (13Weis W.I. Drickamer K. Hendrickson W.A. Nature. 1992; 360: 127-134Crossref PubMed Scopus (852) Google Scholar) the binding of mannose groups to the CRD through the 3- and 4-OH groups Each of these groups a coordination bond with the principal two hydrogen bonds with amino acids that are also The in these crystals are cross-linked by the in which other ligands are soaked into the The crystals of the MBP-C CRD in the of sugar and to the structures of a series of monosaccharides (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). the orientation of monosaccharides bound to MBP-C is to MBP-A (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar) (Fig. the monosaccharides are the two can by around a local symmetry axis that the equatorial 3- and 4-OH groups of mannose or their In this the orientation in the with the of mannose or its equivalent bound to and as orientation (Fig. and the as orientation in which the 4-OH this position (Fig. the MBP-A CRD bound to the trimeric the neck and CRD in the of sugar W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar). the crystals of the trimeric to the binding of ligands to The structure of this as a W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar). In that a of bound at the Ca2+ through vicinal groups in a to that in sugars bound to high or other vicinal groups as with sugar ligands for The which have vicinal to an A structure of the trimeric MBP-A in The protein structure is to that in the presence of the binding two the by the 3- and 4-OH groups of mannose as in MBP-C (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google an Ca2+ The of d-mannose,N-acetyl-d-glucosamine, and l-fucose as as soaked into trimeric MBP-A crystals in the presence of and their structures the bound sugars the set of Ca2+ coordination and hydrogen bonds as in structures of MBP-A and binds in orientation (Fig. the orientation in with In two of the binds in orientation (Fig. and in the binds in orientation (Fig. The structures of the two bound to MBP-A are of the in their affinity for MBP-A Weis W.I. R.A. Drickamer K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). in and bind to MBP-A in the orientation as binds to MBP-C with the and groups to Ca2+. The mutation of His189 to the to Weis W.I. R.A. Drickamer K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). In the present the of the this residue (Fig. whereas in the These data that interactions of the with His189 to the binding and can to The between the of monosaccharides and the of bound to MBP-A the that with crystal formation by the cross-linked complex a in the orientation of the sugars in that the of such oligosaccharides soaked into the crystals of trimeric the structures of crystals soaked with the disaccharides Manα1–3Man and all of which are at the of high mannose The mannose at the of and 3- and 4-OH groups. In these two the of binding in which the and mannose of the are bound at the Ca2+ to at which a analysis of the bound structures in these Manα1–3Man can only bind through the mannose in Manα1–3Man binds to trimeric MBP-A in orientation as in the cross-linked This that the bound orientation is by the of the by crystal A to binding in orientation whereas the sugar in the binds in orientation of orientation at the principal Ca2+ in MBP-A and orientation is in and orientation is in the other affinity and are for as or two are in orientation is in and orientation is in the other K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google In and are for as or in a The two are in the between binding of monosaccharides and oligosaccharides to of to such also in the of MBP-C with The crystal structures of MBP-C soaked with oligosaccharide ligands reveal that Manα1–3Man binds to MBP-C in orientation as oligosaccharides the which is a high affinity MBP-C R.T. Lee Y.C. J. 1997; PubMed Scopus Google the of oligosaccharides the with and a mannose M.S. Lee R.T. Lee Y.C. 1997; PubMed Scopus Google Scholar) In the sugar is bound in orientation the MBP-A binding the MBP-C to to the of the of the The that serve as Ca2+ and sugar ligands are the in the MBP-A and MBP-C (Fig. 1). are two in the sugar binding of these In the in which the a with or of the bound and the of the the of mannose is bound in orientation (Fig. 1). The of the by His189 to binding to whereas the by the His189 binding Weis W.I. R.A. Drickamer K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). The with the is in MBP-C by the in the equivalent residue of MBP-C, The position of the is in MBP-C, which a with the (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). The other in the MBP-A and MBP-C binding is a formed between the of mannose bound in orientation and the of MBP-A The of this by to binding Weis W.I. R.A. Drickamer K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). A residue is at the equivalent residue in of Manα1–3Man and bound to MBP-A that although the with the is the presence of His189 may the to the sugar in these of the by the of S. S. J. 1990; Scopus Google Scholar) that of these two of bound in orientation His189 is for the in the MBP-A His189 and soaked with The of at position in a single orientation bound at independent are in the In two of the independent the sugar is bound in orientation and in the other is bound in orientation I. The resolution of these structures to of orientation bound at a is that one orientation in the of of the bound mannose in orientation I. this residue contributes to the the MBP-A His189 and soaked with Manα1–3Man The also binds in a mixture of although in this a mixture of is in two of the and only orientation is in the The structural are from crystals that in from MBP-C crystals soaked in Manα1–3Man in which can as a its vicinal hydroxyl groups have the stereochemistry for binding at the principal and with the of that the binds in a mixture of and K. and These are with the that the from in In the and by in structure and such as the of a or the higher of a The of the crystals in the presence of a more the indicate that amino acids in the binding can in orientation on the of the into the binding of oligosaccharides to MBP-A by crystals of the trimeric MBP-A in the presence of the asparaginyl oligosaccharide The crystal structure at The of the crystals contains two trimers that are cross-linked by the oligosaccharide The trimers are in in the crystal with the cross-linked by the oligosaccharide (Fig. A single trimer is cross-linked to trimers in the of a trimer is cross-linked to one from The oligosaccharide is in two of the with all mannose (Fig. The and trimers of MBP-A in the The is bound in orientation as in the structure of the oligosaccharide bound to the MBP-A CRD (13Weis W.I. Drickamer K. Hendrickson W.A. Nature. 1992; 360: 127-134Crossref PubMed Scopus (852) Google Scholar). The which bound in the is bound in orientation and The the mannose residue in this one bond from the residue and to the that the presence of His189 is to influence the of the with the sugar in the binding the sugar on this to MBPs affinity in binding to monosaccharides with disaccharides and higher oligosaccharides (12Lee R.T. Ichikawa Y. Fay M. Drickamer K. Shao M.-C. Lee Y.C. J. Biol. Chem. 1991; 266: 4810-4815Abstract Full Text PDF PubMed Google Scholar, Weis W.I. R.A. Drickamer K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, R.T. Lee Y.C. J. 1997; PubMed Scopus Google Scholar). The local symmetry of the 3- and 4-OH groups of mannose and the of that ligands to bind to MBPs in binding orientation in for the to to bind in orientation. The crystal structures are at to of of binding at a at to The data that the MBP with a in only one of the orientations. The basis for this is from the in binding have been for oligosaccharide ligands binding to MBP-C with and in the of binding to mannose of and respectively R.T. Lee Y.C. J. 1997; PubMed Scopus Google Scholar). These data as of a binding on MBP-C that is in which these the structure of bound to MBP-C reveal a binding only the mannose residue interacts with the of the In a binding in a MBP-C CRD crystal soaked in in this the into the structure (14Ng K.K.-S. Drickamer K. Weis W.I. J. Biol. Chem. 1996; 271: 663-674Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar). that this to a at the is that this a binding for The in the binding of MBP-A and MBP-C to oligosaccharides may to the of the MBP-C which a more of the of these ligands. in and the sugar has 3- and 4-OH which the and at the binding have for this of binding in of MBP-A and MBP-C crystals with and two of binding to the one of the two sugars in these an of binding combined with in the to the ligands in MBP-A and MBP-C, the in the binding of MBP-C to and oligosaccharide ligands. that the higher affinity binding of the oligosaccharides to MBP-C a trimeric MBP-C R.T. Lee Y.C. J. 1997; PubMed Scopus Google Scholar, M.S. Lee R.T. Lee Y.C. 1997; PubMed Scopus Google Scholar) that some of the from in the of in MBP-C and that MBPs in binding to a or by the ability of the binding to the orientation of the bound are two or of which in The is that are in in binding such as for MBP-C, that to the is The in is that the specificity for a binding orientation the ability of an MBP to with of an oligosaccharide in crystal structures of oligosaccharides display a of A.J. R.A. Glycobiology. 1999; PubMed Scopus Google and NMR and that although is some in the the of high mannose structures is R.J. R.A. J. Biochem. 1998; PubMed Scopus Google Scholar). a oligosaccharide the binding to a sugar in a orientation to one the binding of sugar to the in orientation the binding of a sugar to by the some of the of binding by the at the that these of in multivalent In the of biological specificity from the ability of the trimer to bind only to the of ligands present on foreign cell to high mannose oligosaccharides present on the host cell W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google Scholar). This from the of the in which the of the CRD with the neck domain the or This is the between mannose on high mannose MBP-A bind to these structures with high The role of binding orientation and its influence on multivalent binding of MBP-A to of sugar on surfaces is at present. Serum MBPs are as higher oligomers into structures with the N-terminal of the trimers cross-linked R. Drickamer K. Biochem. J. 1997; 325: 391-400Crossref PubMed Scopus (54) Google Scholar). that the trimers of in the recognition of the target cell The lateral association of trimers in the crystal (Fig. a of trimer binding an with the that trimers can with of on surfaces. in this one of the crystal represent a cell oligosaccharides for recognition by MBP (Fig. with the trimers in the (Fig. may also in the trimer as by the of the between the collagenous and α-helical neck W.I. Drickamer K. Structure. 1994; 2: 1227-1240Abstract Full Text Full Text PDF PubMed Scopus (291) Google such that the trimers in the can to the by the by MBPs requires with MBP-associated serine of the MBP in serum is with a of the which binding of MBP to surfaces. The that to is is that the association of the collagenous domains of two MBP trimers with a single is for R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The of MBP trimers in the cross-linked crystals that lateral association of the CRD and neck can and that such association stabilized by with surfaces. The association of the neck and CRD fix the of the collagenous a by which the bound to this the of MBP to a target cell We Lee for the high affinity MBP-C ligands. We also for with protein