Crystallization of seed globulins from legumes

Abstract

Seeds contain large quantities of proteins and are therefore main food sources. In the last century, protein extracts of legume seeds were dialysed against distilled water and in some cases small crystals of pure protein appeared. However, those crystals were generally of poor quality with respect to X-ray diffraction. Recently, the crystallization of some of them was improved and the structures of two 7S globulins, phaseolin from Phaseolus vulgaris and canavalin from Canavalia ensiformis, have been determined at 3.0 and 2.6 A resolution, respectively. Efforts to improve the quality of the phaseolin crystals resulted in three new crystal forms which will be discussed in this paper. The only high-resolution X-ray analysis of a seed globulin from legumes is that of narbonin, a 2S protein from Vicia narbonensis. The crystal structure at 1.8 A shows a very compact packing in layers of molecules. The intermolecular contacts include salt bridges and hydrophobic clusters that might facilitate both the aggregation of the molecules and their crystallization. Because the seed globulins appear in large quantities in the protein bodies of the seeds, efficient packing of the molecules similar to the crystal packing can be assumed.

Modeling to Understand Plant Protein Structure-Function Relationships—Implications for Seed Storage Proteins

“…Structurally, the different classes of seed storage proteins can be divided into two types, albumins/globulins and prolamins/glutelins (Figure 1). Albumins and globulins are generally highly structured and thereby able to crystallize, and their folding can be simulated using a range of methods, including machine learning and ab initio modeling [92][93][94][95][96][97][98] (Table 4). Most prolamins and glutelins are instead intrinsically disordered [99], and thereby, pose more challenges in modeling.…”

“…The fact that X-ray diffraction-based models are available, enables simulation-based verification of the protein structures and simplifies further computer-based modeling. Globulins from legume seeds were the first storage protein to be crystallized and evaluated with X-ray diffraction [93][94][95][96]. The crystal structure was found to be compact with salt bridges and hydrophobic clusters, resulting in layers of packed molecules forming aggregates [94].…”

“…Globulins from legume seeds were the first storage protein to be crystallized and evaluated with X-ray diffraction [93][94][95][96]. The crystal structure was found to be compact with salt bridges and hydrophobic clusters, resulting in layers of packed molecules forming aggregates [94]. Since then, homology modeling has been used to model other globulin proteins, e.g., vicilin in cocoa, based on crystal structures of legume globulins such as jack bean canavalin and French bean phaseolin [97] (Table 4).…”

Crystal structure of narbonin at 1.8 Å resolution

“…Until now, no three-dimensional structure for the 11S globulins has been published, although some llS globulins have been crystallized (Hennig & Schlesier, 1994).…”

Insulin-Binding Canavalin Is Present in Canavalia ensiformis Seed Coat

“…Canavalin is a major storage protein from Canavalia seeds and belongs to the vicilin family of seed cotyledonary storage proteins [16,17]. The protein self-organizes into three monomeric units of about 47,000 Da each, perfectly arranged in a threefold axis of symmetry.…”