Crystal structure of a plant albumin from Cicer arietinum (chickpea) possessing hemopexin fold and hemagglutination activity

Abstract

Crystal structure of a reported PA2 albumin from Cicer arietinum shows that it belongs to hemopexin fold family, has four beta-propeller motifs and possesses hemagglutination activity, making it different from known legume lectins. A plant albumin (PA2) from Cicer arietinum, presumably a lectin (CAL) owing to its hemagglutination activity which is inhibited by complex sugars as well as glycoproteins such as fetuin, desialylated fetuin and fibrinogen. The three-dimensional structure of this homodimeric protein has been determined using X-ray crystallography at 2.2 Å in two crystal forms: orthorhombic (P21212) and trigonal (P3). The structure determined using molecular replacement method and refined in orthorhombic crystal form reached R-factors R free 22.6 % and R work 18.2 % and in trigonal form had 22.3 and 17.9 % in the resolution range of 20.0-2.2 and 35.3-2.2 Å, respectively. Interestingly, unlike the known legume lectin fold, the structure of this homodimeric hemagglutinin belonged to hemopexin fold that consisted of four-bladed β-propeller architecture. Each subunit has a central cavity forming a channel, inside of which is lined with hydrophobic residues. The channel also bears binding sites for ligands such as calcium, sodium and chloride ions, iodine atom in the case of iodine derivative and water molecules. However, none of these ligands seem important for the sugar recognition. No monosaccharide sugar specificity could be detected using hemagglutination inhibition. Chemical modification studies identified a potential sugar-binding site per subunit molecule. Comparison of C-alpha atom positions in subunit structures showed that the deviations between the two crystal forms were more with respect to blades I and IV. Differences also existed between subunits in two forms in terms of type and site of ligand binding.

Crystal Structure of Mg2+ Containing Hemopexin-Fold Protein from Kabuli Chana (Chickpea-White, CW-25) at 2.45 Å Resolution Reveals Its Metal Ion Transport Property

“…The CW-25 protein isolated from Cicer arietinum L. is shown to have mild hemagglutination activity [10,13]. It has also been shown to have antifungal activity [10].…”

“…However, CAL protein contained two other metal ions, calcium and sodium in a channel-like structure. This protein was reported with a mild hemagglutination activity [13]. The role of this protein vis-à-vis metal ion was unclear.…”

“…In order to reveal the folding of the polypeptide chain of CW-25 and determine the relationship between its structure and function, we have solved the three-dimensional structure of CW-25. It may be mentioned here that the structure of a similar protein from Chickpea-black (Cicer arietinum, CAL) has been reported recently [13]. The structure determination of CW-25 revealed the presence of two crystallographically independent molecules, A and B in the asymmetric unit.…”

Overview of the Structure–Function Relationships of Mannose-Specific Lectins from Plants, Algae and Fungi

“…An unexpected four-bladed β-propeller structure was found to occur in a PA 2 albumin from chickpea ( Cicer arietinum ), which displays a well documented hemagglutinating activity most probably related to a lectin with an unusual hemopexin fold [171].…”

Biochemical and functional properties of a lectin purified from the seeds of Cicer arietinum L.

“…The previous reports of chickpea lectin on various aspect take account of characterization of a clone encoding vegetative lectin from C. arietinum epicotyls (Esteban et al 2002), production of stable transgene chickpea through expression of insecticidal lectin (Chakraborti et al 2009) and root lectins (Agrawal et al 2011). In addition, in silico studies on recombinant chickpea lectin (Wakankar et al 2013), three dimensional structure determination (Sharma et al 2015), and α-amylase inhibitory activity against potato beetle larvae (Wang et al 2017) are also published in literature domain. Our previous studies reported crystallization and preliminary X-ray characterisation of a lectin from chickpea (Katre et al 2005).…”