Crystal structure of native and Cd/Cd-substituted Dioclea guianensis seed lectin. A novel manganese-binding site and structural basis of dimer-tetramer association

Citation
Da. Wah et al., Crystal structure of native and Cd/Cd-substituted Dioclea guianensis seed lectin. A novel manganese-binding site and structural basis of dimer-tetramer association, J MOL BIOL, 310(4), 2001, pp. 885-894
Citations number
44
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Molecular Biology & Genetics
Journal title
JOURNAL OF MOLECULAR BIOLOGY
ISSN journal
0022-2836 → ACNP
Volume
310
Issue
4
Year of publication
2001
Pages
885 - 894
Database
ISI
SICI code
0022-2836(20010720)310:4<885:CSONAC>2.0.ZU;2-6
Abstract
Diocleinae legume lectins are a group of oligomeric proteins whose subunits display a high degree of primary structure and tertiary fold conservation but exhibit considerable diversity in their oligomerisation modes. To eluci date the structural determinants underlaying Diocleinae lectin oligomerisat ion, we have determined the crystal structures of native and cadmium-substi tuted Dioclea guianensis (Dguia) seed lectin. These structures have been so lved by molecular replacement using concanavalin (ConA) coordinates as the starting model, and refined against data to 2.0 Angstrom resolution. In the native (Mn/Ca-Dguia) crystal form (P4(3)2(1)2), the asymmetric unit contai ns two monomers arranged into a canonical legume lectin dimer, and the tetr amer is formed with a symmetry-related dimer. In the Cd/Cd-substituted form (14(1)22), the asymmetric unit is occupied by a monomer. In both crystal f orms, the tetrameric association is achieved by the corresponding symmetry operators. Like other legume lectins, native D. guianensis lectin contains manganese and calcium ions bound in the vicinity of the saccharide-combinin g site. The architecture of these metal-binding sites (S1 and S2) changed o nly slightly in the cadmium/cadmium-substituted form. A highly ordered calc ium (native lec tin) or cadmium (Cd/Cd-substituted lectin) ion is coordinat ed at the interface between dimers that are not tetrameric partners in a si milar manner as the previously identified Cd2+ in site S3 of a Cd/Ca-ConA. An additional Mn2+ coordination site (called S5), whose presence has not be en reported in crystal structures of any other homologous lectin, is presen t in both, the Mn/Ca and the Cd/Cd-substituted D, guianensis lectin forms. On the other hand, comparison of the primary and quaternary crystal structu res of seed lectins from D. guianensis and Dioclea grandiflora (1DGL) indic ates that the loop comprising residues 117-123 is ordered to make interdime r contacts in the D. grandiflora lectin structure, while this loop is disor dered in the D. guianensis lectin structure. A single amino acid difference at position 131 (histidine in D. grandiflora and asparagine in D, guianens is) drastically reduces interdimer contacts, accounting for the disordered loop. Further, this amino acid change yields a conformation that may explai n why a pH-dependent dimer-tetramer equilibrium exists for the D. guianensi s lectin but not for the D. grandiflora lectin. (C) 2001 Academic Press.