Crystals were obtained after a week using condition No. 29 (0.1 M Na HEPES pH 7.5, 0.8 M sodium potassium tartrate tetrahydrate) of Hampton Crystal Screen I. To optimize the crystallization conditions, the concentration of tartrate was modified and different buffers in various pH ranges were tested. Crystals of good size for diffraction (Fig. 1) were obtained under the conditions 0.1 M Na HEPES pH 7.5–8.5, 0.4–1.2 M sodium potassium tartrate.
Surprisingly, the crystals obtained (Fig. 1) provided a data set extending to 1.87 Å resolution which was scaled in the resolution range 33.150–2.05 Å. The D. rostrata
lectin crystal belongs to the orthorhombic space group I
222, with unit-cell parameters a
= 61.51, b
= 88.22, c
= 87.76 Å. The calculated value for the Matthews coefficient (Matthews, 1968
) based on the molecular weight of 25.5 kDa is 2.4 Å3
, resulting in a solvent content of 47.9%, which corresponds to the presence of a monomer in the asymmetric unit. Data-collection statistics are shown in Table 1. Crystal structure solution is under way.
Statistics of data collection
Sequence alignment of fragment 2 from D. rostrata
lectin (SWISS-PROT code P58908) with D. guianensis
lectin (PDB code 1h9p
, chain A
; Calvete et al.
) and D. grandiflora
lectin (PDB code 1dgl
, chain B
; Rozwarski et al.
) showed that DRL contains an Asn residue in position 131, while D. grandiflora
lectin contains a His residue in this position (Fig. 2). Comparison of the structures of D. guianensis
lectin, which presents pH-dependent oligomerization, and D. grandiflora
lectin, which does not display a dimer–tetramer equilibrium, indicated that substitution of His131 for Asn drastically reduces interdimer contacts and disorders the loop comprising residues 117–123 which, in its ordered conformation, stabilizes the pH-independent tetrameric association of the D. grandiflora
lectin (Wah et al.
). The solution of the DRL crystal structure may be useful to determine whether DRL presents the same features as D. guianensis
regarding the dimer–tetramer association. Since only the tetravalent form is able to cause cross-linking of receptors on the cell surface, the different ratio of divalent and tetravalent lectin species at a given pH may contribute to the variability of biological functions.
Sequence alignment of the lectin segment 119–142 from D. rostrata (DRL), D. guianensis (Dgui) and D. grandiflora (DGL). Asterisks (*) related to conserved residues and colons (:) to semi-conserved residues.