Structural Investigation of a Novel N-Acetyl Glucosamine Binding Chi-Lectin Which Reveals Evolutionary Relationship with Class III Chitinases

Abstract

The glycosyl hydrolase 18 (GH18) family consists of active chitinases as well as chitinase like lectins/proteins (CLPs). The CLPs share significant sequence and structural similarities with active chitinases, however, do not display chitinase activity. Some of these proteins are reported to have specific functions and carbohydrate binding property. In the present study, we report a novel chitinase like lectin (TCLL) from Tamarindus indica. The crystal structures of native TCLL and its complex with N-acetyl glucosamine were determined. Similar to the other CLPs of the GH18 members, TCLL lacks chitinase activity due to mutations of key active site residues. Comparison of TCLL with chitinases and other chitin binding CLPs shows that TCLL has substitution of some chitin binding site residues and more open binding cleft due to major differences in the loop region. Interestingly, the biochemical studies suggest that TCLL is an N-acetyl glucosamine specific chi-lectin, which is further confirmed by the complex structure of TCLL with N-acetyl glucosamine complex. TCLL has two distinct N-acetyl glucosamine binding sites S1 and S2 that contain similar polar residues, although interaction pattern with N-acetyl glucosamine varies extensively among them. Moreover, TCLL structure depicts that how plants utilize existing structural scaffolds ingenuously to attain new functions. To date, this is the first structural investigation of a chi-lectin from plants that explore novel carbohydrate binding sites other than chitin binding groove observed in GH18 family members. Consequently, TCLL structure confers evidence for evolutionary link of lectins with chitinases.

A Nontoxic Polypeptide Oligomer with a Fungicide Potency under Agricultural Conditions Which Is Equal or Greater than That of Their Chemical Counterparts

“…In plants, the chitin-binding proteins, one family of antifungal proteins, are usually divided in two classes: class I proteins contain a chitin-binding domain similar to a domain present in hevein, a protein from rubber latex [ 8 ]; class II proteins lack the chitin-binding hevein domain [ 7 , 8 ]. The antifungal activity of chitin-binding proteins is mainly due to their ability to bind fungal cell wall chitin, which results in disruption of cell polarity and consequent inhibition of growth by mechanisms that have not been elucidated [ 9 ]. The antifungal activity displayed by chitinases, another family of antifungal proteins, was originally assumed to derive from their ability to catalytically cleave chitin, leading to a weakened fungal cell wall and subsequent cell lysis.…”

Flax rhamnogalacturonan lyases: phylogeny, differential expression and modeling of protein structure

“…Sequence diversity in PL4 may reflect variations in the patterns of arabinan and galactan side chains of RG-Is from different species (McDonough et al 2004). Moreover, molecular evolution could affect the catalytic activity of the enzyme such that its function might be substantially modified or even lost (Kozlova et al 2017), as has occurred with chitinase-like proteins (Patil et al 2013).…”

Purification and Characterization of 2S Albumin from Seeds of Wrightia tinctoria Exhibiting Antibacterial and DNase Activity

“…Plant seeds have globulins, chitinases, Kunitz-type inhibitors, β-1,3-glucanses, defensins, lipid transfer proteins, ribosomes inactivating proteins and 2S albumins which help them during seedling growth, development and to provide protection against pathogens [6][7][8][9][10][11][12][13][14][15].…”

“…2S albumins are water-soluble seed storage proteins (SSPs) belonging to the prolamin superfamily, which are widely distributed among mono-and dicotyledonous plants [22,23]. Prolamins are categorized as either based on the electromobility on SDS-PAGE gels as (10,13,and 16 kDa) or based on amino acid sequence similarity maize γ2-zein type (16 and 13 kDa prolamins) or δ-zeins (10 kDa prolamins) [24]. These proteins are synthesized over rough ER and transported inside the lumen where they undergo proteolytic cleavage of N-terminal and C-terminal signal sequence; and forms disulfide bonds [25,26].…”