Molecular Basis of Sugar Recognition by the Human L-type Lectins ERGIC-53, VIPL, and VIP36

ERGIC-53, VIPL, and VIP36 are related type 1 membrane proteins of the mammalian early secretory pathway. They are classified as L-type lectins because of their luminal carbohydrate recognition domain, which exhibits homology to leguminous lectins. These L-type lectins have different intracellular distributions and dynamics in the endoplasmic reticulum-Golgi system of the secretory pathway and interact with N-glycans of glycoproteins in a Ca2+-dependent manner, suggesting a role in glycoprotein sorting and trafficking. To understand the function of these lectins, knowledge of their carbohydrate specificity is crucial but only available for VIP36 (Kamiya, Y., Yamaguchi, Y., Takahashi, N., Arata, Y., Kasai, K. I., Ihara, Y., Matsuo, I., Ito, Y., Yamamoto, K., and Kato, K. (2005) J. Biol. Chem. 280, 37178–37182). Here we provide a comprehensive and quantitative analysis of sugar recognition of the carbohydrate recognition domains of ERGIC-53 and VIPL in comparison with VIP36 using a pyridylaminated sugar library in conjunction with frontal affinity chromatography. Frontal affinity chromatography revealed selective interaction of VIPL and VIP36 with the deglucosylated trimannose in the D1 branch of high-mannose-type oligosaccharides but with different pH dependence. ERGIC-53 bound high-mannose-type oligosaccharides with low affinity and broad specificity, not discriminating between monoglucosylated and deglucosylated high-mannosetype oligosaccharides. Based on the sugar-binding properties in conjunction with known features of these proteins, we propose a model for the action of the three lectins in glycoprotein guidance and trafficking. Moreover, structure-based mutagenesis revealed that the sugar-binding properties of these L-type lectins can be switched by single amino acid substitutions. ERGIC-53, VIPL, and VIP36 are related type 1 membrane proteins of the mammalian early secretory pathway. They are classified as L-type lectins because of their luminal carbohydrate recognition domain, which exhibits homology to leguminous lectins. These L-type lectins have different intracellular distributions and dynamics in the endoplasmic reticulum-Golgi system of the secretory pathway and interact with N-glycans of glycoproteins in a Ca2+-dependent manner, suggesting a role in glycoprotein sorting and trafficking. To understand the function of these lectins, knowledge of their carbohydrate specificity is crucial but only available for VIP36 (Kamiya, Y., Yamaguchi, Y., Takahashi, N., Arata, Y., Kasai, K. I., Ihara, Y., Matsuo, I., Ito, Y., Yamamoto, K., and Kato, K. (2005) J. Biol. Chem. 280, 37178–37182). Here we provide a comprehensive and quantitative analysis of sugar recognition of the carbohydrate recognition domains of ERGIC-53 and VIPL in comparison with VIP36 using a pyridylaminated sugar library in conjunction with frontal affinity chromatography. Frontal affinity chromatography revealed selective interaction of VIPL and VIP36 with the deglucosylated trimannose in the D1 branch of high-mannose-type oligosaccharides but with different pH dependence. ERGIC-53 bound high-mannose-type oligosaccharides with low affinity and broad specificity, not discriminating between monoglucosylated and deglucosylated high-mannosetype oligosaccharides. Based on the sugar-binding properties in conjunction with known features of these proteins, we propose a model for the action of the three lectins in glycoprotein guidance and trafficking. Moreover, structure-based mutagenesis revealed that the sugar-binding properties of these L-type lectins can be switched by single amino acid substitutions. Growing evidence indicates that N-glycans function as tags recognized by a variety of intracellular lectins that govern the fates of glycoproteins in eukaryotes (1Spiro R.G. CMLS Cell. Mol. Life Sci. 2004; 61: 1025-1041Crossref PubMed Scopus (133) Google Scholar, 2Helenius A. Aebi M. Annu. Rev. Biochem. 2004; 73: 1019-1049Crossref PubMed Scopus (1580) Google Scholar, 3Kamiya Y. Kato K. Trends Glycosci. Glycotechnol. 2006; 18: 231-244Crossref Scopus (10) Google Scholar, 4Kato K. Kamiya Y. Glycobiology. 2007; 17: 1031-1044Crossref PubMed Scopus (47) Google Scholar). These lectins are postulated to interact specifically with partially trimmed intermediates of high-mannose-type oligosaccharides displayed on the target polypeptide and thereby to control protein translocation, folding, degradation, and trafficking. The lectins calreticulin and calnexin assist in the folding process of nascent proteins in the endoplasmic reticulum (ER) 5The abbreviations used are: ERendoplasmic reticulumERGICER-Golgi intermediate compartmentCRDcarbohydrate recognition domainFACfrontal affinity chromatographyPApyridylaminatedMES4-morpholineethanesulfonic acidERGIC-5353-kDa membrane protein of the ER-Golgi intermediate compartmentVIP36vesicular integral protein of 36 kDaVIPLVIP36-like. 5The abbreviations used are: ERendoplasmic reticulumERGICER-Golgi intermediate compartmentCRDcarbohydrate recognition domainFACfrontal affinity chromatographyPApyridylaminatedMES4-morpholineethanesulfonic acidERGIC-5353-kDa membrane protein of the ER-Golgi intermediate compartmentVIP36vesicular integral protein of 36 kDaVIPLVIP36-like. by capturing their monoglucosylated high-mannosetype oligosaccharides after the action of glucosidase I (1Spiro R.G. CMLS Cell. Mol. Life Sci. 2004; 61: 1025-1041Crossref PubMed Scopus (133) Google Scholar, 2Helenius A. Aebi M. Annu. Rev. Biochem. 2004; 73: 1019-1049Crossref PubMed Scopus (1580) Google Scholar, 3Kamiya Y. Kato K. Trends Glycosci. Glycotechnol. 2006; 18: 231-244Crossref Scopus (10) Google Scholar, 4Kato K. Kamiya Y. Glycobiology. 2007; 17: 1031-1044Crossref PubMed Scopus (47) Google Scholar, 5Parodi A.J. Annu. Rev. Biochem. 2000; 69: 69-93Crossref PubMed Scopus (531) Google Scholar, 6Williams D.B. J. Cell Sci. 2006; 119: 615-623Crossref PubMed Scopus (366) Google Scholar). Glucosidase II then removes the remaining glucose residue at the non-reducing terminal of the D1 branch of the substrate glycoproteins, giving rise to the M9 glycoform (the oligosaccharides are designated as shown in Fig. 1) that is no longer capable of interacting with calreticulin and calnexin (1Spiro R.G. CMLS Cell. Mol. Life Sci. 2004; 61: 1025-1041Crossref PubMed Scopus (133) Google Scholar, 2Helenius A. Aebi M. Annu. Rev. Biochem. 2004; 73: 1019-1049Crossref PubMed Scopus (1580) Google Scholar, 3Kamiya Y. Kato K. Trends Glycosci. Glycotechnol. 2006; 18: 231-244Crossref Scopus (10) Google Scholar, 4Kato K. Kamiya Y. Glycobiology. 2007; 17: 1031-1044Crossref PubMed Scopus (47) Google Scholar, 7Totani K. Ihara Y. Matsuo I. Ito Y. J. Biol. Chem. 2006; 281: 31502-31508Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar). During the folding process, incompletely folded glycoproteins are re-glucosylated by the folding sensor UTP-diphosphate-glucose:glycoprotein glucosyltransferase (1Spiro R.G. CMLS Cell. Mol. Life Sci. 2004; 61: 1025-1041Crossref PubMed Scopus (133) Google Scholar, 2Helenius A. Aebi M. Annu. Rev. Biochem. 2004; 73: 1019-1049Crossref PubMed Scopus (1580) Google Scholar, 3Kamiya Y. Kato K. Trends Glycosci. Glycotechnol. 2006; 18: 231-244Crossref Scopus (10) Google Scholar, 4Kato K. Kamiya Y. Glycobiology. 2007; 17: 1031-1044Crossref PubMed Scopus (47) Google Scholar). Successful folding of glycoproteins in the ER can be achieved through multiple rounds of the calreticulin/calnexin cycle. endoplasmic reticulum ER-Golgi intermediate compartment carbohydrate recognition domain frontal affinity chromatography pyridylaminated 4-morpholineethanesulfonic acid 53-kDa membrane protein of the ER-Golgi intermediate compartment vesicular integral protein of 36 kDa VIP36-like. endoplasmic reticulum ER-Golgi intermediate compartment carbohydrate recognition domain frontal affinity chromatography pyridylaminated 4-morpholineethanesulfonic acid 53-kDa membrane protein of the ER-Golgi intermediate compartment vesicular integral protein of 36 kDa VIP36-like. After correct folding, secretory glycoproteins are transported to the Golgi complex via the ER-Golgi intermediate compartment (ERGIC) by vesicular transport. ER export of some proteins is facilitated by cargo receptors. The most completely characterized cargo receptor is the type 1 membrane lectin ERGIC-53, which, together with ERGL, VIP36, and VIPL, constitutes the family of leguminous type (L-type) lectins (8Nufer O. Mitrovic S. Hauri H.P. J. Biol. Chem. 2003; 278: 15886-15896Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). L-type lectins possess a luminal carbohydrate recognition domain (CRD) that binds to high-mannose-type oligosaccharides in a Ca2+-dependent manner (9Appenzeller-Herzog C. Roche A.C. Nufer O. Hauri H.P. J. Biol. Chem. 2004; 279: 12943-12950Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar, 10Kamiya Y. Yamaguchi Y. Takahashi N. Arata Y. Kasai K.I. Ihara Y. Matsuo I. Ito Y. Yamamoto K. Kato K. J. Biol. Chem. 2005; 280: 37178-37182Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar, 11Yamaguchi D. Kawasaki N. Matsuo I. Totani K. Tozawa H. Matsumoto N. Ito Y. Yamamoto K. Glycobiology. 2007; 17: 1061-1069Crossref PubMed Scopus (21) Google Scholar). ERGIC-53, the most popular marker for the ERGIC, cycles between ER and ERGIC and operates as a cargo receptor in ER export of some glycoproteins, including the lysosomal glycoproteins cathepsin C and cathepsin Z (12Appenzeller C. Andersson H. Kappeler F. Hauri H.P. Nat. Cell Biol. 1999; 1: 330-334Crossref PubMed Scopus (267) Google Scholar, 13Hauri H.P. Kappeler F. Andersson H. Appenzeller C. J. Cell Sci. 2000; 113: 587-596Crossref PubMed Google Scholar, 14Appenzeller-Herzog C. Nyfeler B. Burkhard P. Santamaria I. Lopez-Otin C. Hauri H.P. Mol. Biol. Cell. 2005; 16: 1258-1267Crossref PubMed Scopus (59) Google Scholar). Polymerization of IgM is also assisted by ERGIC-53 (15Anelli T. Ceppi S. Bergamelli L. Cortini M. Masciarelli S. Valetti C. Sitia R. EMBO J. 2007; 26: 4177-4188Crossref PubMed Scopus (104) Google Scholar). This lectin forms a complex with MCFD2 (multi-coagulation factor deficiency 2), a 16-kDa protein possessing two EF-hand domains, and thereby recruits blood coagulation factors V and VIII (16Zhang B. Cunningham M.A. Nichols W.C. Bernat J.A. Seligsohn U. Pipe S.W. McVey J.H. Schulte-Overberg U. de Bosch N.B. Ruiz-Saez A. White G.C. Tuddenham E.G. Kaufman R.J. Ginsburg D. Nat. Genet. 2003; 34: 220-225Crossref PubMed Scopus (215) Google Scholar, 17Nyfeler B. Michnick S.W. Hauri H.P. Proc. Natl. Acad. Sci. U. S. A. 2005; 102: 6350-6355Crossref PubMed Scopus (158) Google Scholar, 18Zhang B. Kaufman R.J. Ginsburg D. J. Biol. Chem. 2005; 280: 25881-25886Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar, 19Nyfeler B. Zhang B. Ginsburg D. Kaufman R.J. Hauri H.P. Traffic. 2006; 7: 1473-1481Crossref PubMed Scopus (61) Google Scholar). VIP36 is concentrated in the cis-Golgi but undergoes complex glycosylation, suggesting that this lectin has access to the medial/trans-Golgi. Whereas VIP36 cycles between the Golgi and the ER, VIPL is a resident of the ER (8Nufer O. Mitrovic S. Hauri H.P. J. Biol. Chem. 2003; 278: 15886-15896Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar, 13Hauri H.P. Kappeler F. Andersson H. Appenzeller C. J. Cell Sci. 2000; 113: 587-596Crossref PubMed Google Scholar, 20Fullekrug J. Scheiffele P. Simons K. J. Cell Sci. 1999; 112: 2813-2821Crossref PubMed Google Scholar, 21Neve E.P. Svensson K. Fuxe J. Pettersson R.F. Exp. Cell Res. 2003; 288: 70-83Crossref PubMed Scopus (49) Google Scholar). Thus, these three lectins have distinct localizations within the early secretory pathway, pointing to disparate functions despite the structural similarities of their CRDs (supplemental Fig. S1). To understand the molecular function of these lectins, it is essential to know the sugar recognition features of their CRDs in detail. In a previous study (10Kamiya Y. Yamaguchi Y. Takahashi N. Arata Y. Kasai K.I. Ihara Y. Matsuo I. Ito Y. Yamamoto K. Kato K. J. Biol. Chem. 2005; 280: 37178-37182Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar), we elucidated the sugar-binding properties of VIP36 by the frontal affinity chromatography (FAC) method using a pyridylaminated (PA) sugar library. In the present study, we used the FAC method to comprehensively and quantitatively analyze the sugar recognition of ERGIC-53 and VIPL in comparison with that of VIP36. Furthermore, on the basis of the recently reported crystal structure of VIP36 (22Satoh T. Cowieson N.P. Hakamata W. Ideo H. Fukushima K. Kurihara M. Kato R. Yamashita K. Wakatsuki S. J. Biol. Chem. 2007; 282: 28246-28255Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar), we created rationally designed VIP36-CRD mutants with altered sugar-binding specificity and pH dependence. Protein Expression—The DNA fragments for residues 1–275 and 1–304, corresponding to the signal sequences and the CRDs of human ERGIC-53 and VIPL, respectively, were cloned into the BamHI and XbaI sites of the pDNA3.1 vector (GE Healthcare) with a C-terminal poly-His tag moiety. HEK293 cells transfected by the calcium phosphate precipitation method were grown in a 1:1 mixture of Dulbecco's modified Eagle's medium and nutrient mixture F-12 supplemented with 10% fetal bovine serum, 1% minimum Eagle's medium 100 IU/ml penicillin, 100 μg/ml streptomycin, and 10 mm sodium pyruvate at 37 °C with 10% CO2 in humidified air. To enhance the expression levels, 2 mm butyrate was added 2 days before harvesting the medium. The poly-His fusion proteins were purified from the cultured medium with a Ni2+-Sepharose high performance column (GE Healthcare). The proteins were further purified using a Superdex 75 gel filtration column (GE Healthcare). The CRD of human VIP36 encoding amino acid residues 45–296 was mutated using the QuikChange method (Stratagene) with the following primers: D261G, 5′-GCCGGCACCGGCGGCCTGTCTGACAATC-3′; and 168K169, 5′-CCCAATGATGAGAAGACCACTGAGCGC-3′. The wild-type or mutant VIP36-CRD with a C-terminal poly-His tag moiety was expressed by Escherichia coli as described previously (10Kamiya Y. Yamaguchi Y. Takahashi N. Arata Y. Kasai K.I. Ihara Y. Matsuo I. Ito Y. Yamamoto K. Kato K. J. Biol. Chem. 2005; 280: 37178-37182Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar). Frontal Affinity Chromatography—FAC analyses were carried out according to the literature (23Kasai K. Oda Y. Nishikawa M. Ishii S. J. Chromatogr. 1986; 376: 33-47Crossref PubMed Scopus (202) Google Scholar, 24Arata Y. Hirabayashi J. Kasai K. J. Biol. Chem. 2001; 276: 3068-3077Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar, 25Hirabayashi J. Arata Y. Kasai K. Methods Enzymol. 2003; 362: 353-368Crossref PubMed Scopus (96) Google Scholar). In the previous study, we conducted FAC analyses of VIP36-CRD immobilized on a HiTrap NHS-activated column (GE Healthcare). However, ERGIC-53-CRD immobilized by this procedure did not show any sugar-binding affinity, presumably because the lysine residues located near the sugar-binding site were unavoidably involved in the amine coupling, rendering the CRD inactive. For this reason, in the present study the recombinant CRDs were immobilized through their histidine tag for FAC analyses except for experiments to examine pH dependence of sugar binding of VIPL and VIP36 (and its mutant). Hence, recombinant proteins were immobilized on a Ni2+-Sepharose high performance or a HiTrap NHS-activated column following the manufacturer's instructions. After immobilization, the Sepharose beads were packed into a stainless steel column (4.0 × 10 mm; GL Sciences). The PA oligosaccharide library was constructed as described previously (10Kamiya Y. Yamaguchi Y. Takahashi N. Arata Y. Kasai K.I. Ihara Y. Matsuo I. Ito Y. Yamamoto K. Kato K. J. Biol. Chem. 2005; 280: 37178-37182Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar). As a new member of this library, Manα1–6(Manα1–3)Manα1–6(Glcα1–3Manα1–2Manα1–2Manα1–3)Manβ1–4GlcNAcβ1–4GlcNAc-PA (designated as GM7) was produced by digestion of GlcMan9GlcNAc2-PA using 30 of for 1 of the oligosaccharide in 100 of pH at 37 °C for and by high performance chromatography using a gel column the PA sugar library used in the present study of high-mannose-type oligosaccharides. PA oligosaccharides were at a of 10 in 10 mm or 10 mm mm and 1 mm and the column at a of at The was by the at at The with the control oligosaccharide was using the of The of the lectins for was by the analysis using 1 as described previously Y. Hirabayashi J. Kasai K. J. Biol. Chem. 2001; 276: 3068-3077Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar), 1) and are the of the PA the of the control and the of immobilized lectins in the The was by at to by the high of the PA For the of was was on the at of The affinity of oligosaccharide was is with using To and were used as control for the analyses of and the are the of three of a of PA oligosaccharides after to the immobilized column at pH the of the PA oligosaccharides be In a the FAC were for ERGIC-53-CRD and were for M9 from the of according to 1 and then for PA oligosaccharides on the basis of their The for the different PA oligosaccharides at pH are in Fig. The show that the sugar-binding specificity of the is to that of the VIPL and VIP36 bound high-mannose-type oligosaccharides the D1 and of this branch of the and the interaction is that the pH dependence of sugar binding was different for VIP36 and VIPL VIP36-CRD exhibits a pH dependence of binding to M9 with pH of as reported previously (10Kamiya Y. Yamaguchi Y. Takahashi N. Arata Y. Kasai K.I. Ihara Y. Matsuo I. Ito Y. Yamamoto K. Kato K. J. Biol. Chem. 2005; 280: 37178-37182Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar), the of VIPL for this oligosaccharide with pH from to of sugar-binding properties of VIPL was shown in previous binding D. Kawasaki N. Matsuo I. Totani K. Tozawa H. Matsumoto N. Ito Y. Yamamoto K. Glycobiology. 2007; 17: 1061-1069Crossref PubMed Scopus (21) Google Scholar). ERGIC-53 bound high-mannose-type oligosaccharides with for VIPL and VIP36 and a to oligosaccharides ERGIC-53 is to or of the residue at the non-reducing terminal of the D1 the three L-type lectins distinct sugar-binding properties despite the structural of their of to the amino acid residues for the in the sugar-binding properties of the lectins on the basis of the recently reported crystal of the VIP36-CRD in comparison with that of the ERGIC-53-CRD (22Satoh T. Cowieson N.P. Hakamata W. Ideo H. Fukushima K. Kurihara M. Kato R. Yamashita K. Wakatsuki S. J. Biol. Chem. 2007; 282: 28246-28255Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar, Svensson K. Pettersson R.F. Y. J. Mol. Biol. 2003; PubMed Scopus Google Scholar). The structure of the VIP36-CRD with that the D1 branch is in a the site with of with and which are L-type lectins (supplemental Fig. (22Satoh T. Cowieson N.P. Hakamata W. Ideo H. Fukushima K. Kurihara M. Kato R. Yamashita K. Wakatsuki S. J. Biol. Chem. 2007; 282: 28246-28255Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar). This the of is a for the binding to three lectins. In with and to between and the non-reducing terminal glucose is in ERGIC-53 and VIPL, is with in ERGIC-53 but not of the crystal indicates that this amino acid in the of the rendering the sugar-binding of ERGIC-53 (supplemental Fig. that the structural by the of the D1 the of the glucose residue in To we produced a VIP36-CRD and its sugar-binding The FAC in Fig. that the mutant VIP36-CRD can the monoglucosylated high-mannose-type oligosaccharides. These that the high specificity of VIP36 and VIPL for the deglucosylated D1 branch is by the single residue in their sugar-binding The pH dependence of sugar binding is a of the L-type lectins. ERGIC-53 (8Nufer O. Mitrovic S. Hauri H.P. J. Biol. Chem. 2003; 278: 15886-15896Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar), VIPL binds oligosaccharides but not at VIP36 exhibits a pH dependence of binding to M9 with a pH (10Kamiya Y. Yamaguchi Y. Takahashi N. Arata Y. Kasai K.I. Ihara Y. Matsuo I. Ito Y. Yamamoto K. Kato K. J. Biol. Chem. 2005; 280: 37178-37182Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar). mutagenesis have that of the histidine residue located in the in the of human ERGIC-53 in is for the in their sugar binding pH (9Appenzeller-Herzog C. Roche A.C. Nufer O. Hauri H.P. J. Biol. Chem. 2004; 279: 12943-12950Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar). The corresponding histidine is in and is to be for the in affinity of this lectin the The pH dependence of VIP36 be to a single of the crystal structure of VIP36 that in and the sugar-binding site are in is that lysine residue near the sugar-binding site of (supplemental Fig. S1). This to a mutant VIP36-CRD in which a lysine residue is into the corresponding between and FAC analysis that this designated as 168K169, the sugar-binding of the type but no longer the pH it a in affinity for M9 with VIPL The model of VIP36-CRD with on the crystal structure indicates that the is not in with the (supplemental Fig. (22Satoh T. Cowieson N.P. Hakamata W. Ideo H. Fukushima K. Kurihara M. Kato R. Yamashita K. Wakatsuki S. J. Biol. Chem. 2007; 282: 28246-28255Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar). This that the of the lysine the affinity at for the in the pH dependence of sugar binding between VIP36 and the present study, we have the sugar-binding and pH dependence of VIPL, ERGIC-53, and VIP36. VIP36, VIPL specifically with the deglucosylated trimannose in the D1 ERGIC-53 binds high-mannose-type oligosaccharides with broad in FAC ERGIC-53 did not between the monoglucosylated and deglucosylated a previous study that this lectin exhibits binding to glycoprotein cargo after of cells with the glucosidase (12Appenzeller C. Andersson H. Kappeler F. Hauri H.P. Nat. Cell Biol. 1999; 1: 330-334Crossref PubMed Scopus (267) Google Scholar). for this is that rise to which not into the sugar-binding site of can the sugar-binding properties in the study be into propose the following model for the function of the three lectins. VIPL binds deglucosylated high-mannose-type glycoproteins after their from the calreticulin/calnexin its ER and its high for binding the D1 are VIPL the folded glycoproteins from by ER and interaction with the family of and binding to is a in of glycoproteins M. Nat. Chem. Biol. 2007; PubMed Scopus Google Scholar). Hence, interaction with VIPL the of folded VIPL is a resident protein of the ER, its interaction with secretory glycoproteins be but is cargo from VIPL for ER known of cargo a in as by between the membrane and is no of pH within the of VIPL is known to ERGIC-53 to the ER, suggesting interaction and between these two lectins (8Nufer O. Mitrovic S. Hauri H.P. J. Biol. Chem. 2003; 278: 15886-15896Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar, 21Neve E.P. Svensson K. Fuxe J. Pettersson R.F. Exp. Cell Res. 2003; 288: 70-83Crossref PubMed Scopus (49) Google Scholar). is that the glycoproteins are to a process to because the affinity of the ERGIC-53-CRD is that of the In ERGIC-53 forms A. J.A. T. L. Hauri H.P. J. Cell Biol. PubMed Scopus Google Scholar), which its Moreover, the binding of cargo glycoproteins to ERGIC-53 can be by as by cathepsin which binds not only through a high-mannose-type but also by a H.P. Kappeler F. Andersson H. Appenzeller C. J. Cell Sci. 2000; 113: 587-596Crossref PubMed Google Scholar). In ERGIC-53 forms a complex with for as known for coagulation factors V and The binding to and polypeptide to be the basis for the selective cargo receptor function of In the of interaction ERGIC-53 glycoprotein with only low via its lectin This is by the that ER-Golgi of glycoproteins N-glycans is ERGIC-53 is in the K. and H. P. is that the of ERGIC-53 ER the export of glycoprotein cargo M. Nat. Chem. Biol. 2007; PubMed Scopus Google Scholar, A. J.A. T. L. Hauri H.P. J. Cell Biol. PubMed Scopus Google Scholar). The broad specificity of ERGIC-53 for high-mannose-type be for of proteins from the ER in this of The on VIP36 previous the function of VIP36 (10Kamiya Y. Yamaguchi Y. Takahashi N. Arata Y. Kasai K.I. Ihara Y. Matsuo I. Ito Y. Yamamoto K. Kato K. J. Biol. Chem. 2005; 280: 37178-37182Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar, H. Appenzeller C. F. Nufer O. 2000; PubMed Scopus Google Scholar). of a pH corresponding to the luminal pH of the Golgi and for the D1 VIP36 glycoproteins to the ER that have control in the VIP36 is postulated to in In the L-type lectins VIPL, ERGIC-53, and VIP36 structural similarities in their CRDs but distinct sugar-binding and which can be by The of sugar specificity and pH dependence is to provide the molecular basis for different functions of the three lectins in and control of also that the carbohydrate of these lectins can be switched by single amino acid substitutions. Kasai and Arata for and Wakatsuki and for the of the structural model for binding between VIP36-CRD and high-mannose-type with