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Xenopus laevis embryonic epidermal lectin in complex with glycerol phosphateXenopus laevis embryonic epidermal lectin in complex with glycerol phosphate
Structural highlights
FunctionITLN1_XENLA Lectin that specifically recognizes microbial carbohydrate chains in a calcium-dependent manner (PubMed:26755729). Binds to microbial glycans that contain a terminal acyclic 1,2-diol moiety, including beta-linked D-galactofuranose (beta-Galf) and D-phosphoglycerol-modified glycans (PubMed:26755729). Binds to S.pneumoniae serotypes with glycans that contain beta-linked D-galactofuranose (beta-Galf) and with D-phosphoglycerol-modified glycans (PubMed:26755729). Can bind a variety of monosaccharides (in vitro) (PubMed:15537792). Probably plays a role in the defense system against microorganisms (Probable).[1] [2] Publication Abstract from PubMedIntelectins (X-type lectins) are broadly distributed throughout chordates, and they have been implicated in innate immunity. Xenopus laevis embryonic epidermal lectin (XEEL), an intelectin secreted into environmental water by the X. laevis embryo, is postulated to function as a defense against microbes. XEEL is homologous (64% identical) to human intelectin-1 (hIntL-1), which is also implicated in innate immune defense. We previously showed that hIntL-1 binds microbial glycans bearing exocyclic vicinal diol groups. It is unknown whether XEEL has the same ligand specificity. Also unclear is whether XEEL and hIntL-1 have similar quaternary structures, as XEEL lacks the corresponding cysteine residues in hIntL-1 that stabilize the disulfide-linked trimer. These observations prompted us to further characterize XEEL. We found that hIntL-1 and XEEL have similar structural features. Even without the corresponding intermolecular disulfide bonds present in hIntL-1, the carbohydrate recognition domain of XEEL (XEELCRD) forms a stable trimer in solution. The structure of XEELCRD in complex with D-glycerol-1-phosphate, a residue present in microbe-specific glycans, indicated the exocyclic vicinal diol coordinates to a protein-bound calcium ion. This ligand-binding mode is conserved between XEEL and hIntL-1. The domain architecture of full length XEEL is reminiscent of a barbell, with two sets of three glycan-binding sites directed in opposite directions. This orientation is consistent with our observation that XEEL can promote the agglutination of specific serotypes of Streptococcus pneumoniae. These data support a role for XEEL in innate immunity, and they highlight structural and functional conservation of X-type lectins among chordates. Structures of Xenopus embryonic epidermal lectin reveal a conserved mechanism of microbial glycan recognition.,Wangkanont K, Wesener DA, Vidani JA, Kiessling LL, Forest KT J Biol Chem. 2016 Jan 11. pii: jbc.M115.709212. PMID:26755729[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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