1gnz: Difference between revisions

Seeds from the African legume shrub Griffonia simplicifolia contain, several lectins. Among them the tetrameric lectin GS I-B(4) has strict, specificity for terminal alpha Gal residues, whereas the closely related, lectin GS I-A(4) can also bind to alpha GalNAc. These two lectins are, commonly used as markers in histology or for research in, xenotransplantation. To elucidate the basis for the fine difference in, specificity, the amino acid sequences of both lectins have been determined, and show 89% identity. The crystal structure of GS I-B(4), determined at, 2.5-A resolution, reveals a new quaternary structure that has never been, observed in other legume lectins. An unexpected loss of both Ca(2+) and, Mn(2+) ions, which are necessary for carbohydrate binding in legume, lectins, may be related to a particular amino acid sequence Pro-Glu-Pro in, the metal binding loop. Comparison with demetallized concanavalin A, reveals a different process for the loss of metal ions and for the, subsequent loss of carbohydrate binding activity. The GS I-A x alpha, GalNAc and GS I-B x alpha Gal complexes were constructed using homology, modeling and docking approaches. The unusual presence of an aromatic amino, acid at position 47 (Tyr in I-A and Trp in I-B) explains the strong, preference for alpha-anomeric sugars in both isolectins. Alteration at one, amino acid position, Ala(106) in I-A versus Glu(106) in I-B, is the basis, for the observed specificities toward alpha GalNAc and alpha Gal.

1GNZ is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Griffonia_simplicifolia Griffonia simplicifolia] with NAG and PO4 as [http://en.wikipedia.org/wiki/ligands ligands]. Structure known Active Site: AC1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1GNZ OCA].  

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