Abstract
Salinity is one of the major stresses affecting rice production worldwide, and various strategies are being employed to increase salt tolerance. Recently, there has been resurgence of interest to characterize SalTol QTL harbouring number of critical genes involved in conferring salt stress tolerance in rice. The present study reports the structure of SALT, a SalTol QTL encoded protein by X-ray crystallography (PDB ID: 5GVY; resolution 1.66 Å). Each SALT chain was bound to one mannose via 8 hydrogen bonds. Compared to previous structure reported for similar protein, our structure showed a buried surface area of 900 Å2 compared to only 240 Å2 for previous one. Small-angle X-ray scattering (SAXS) data analysis showed that the predominant solution shape of SALT protein in solution is also dimer characterized by a radius of gyration and maximum linear dimension of 2.1 and 6.5 nm, respectively. The SAXS profiles and modelling confirmed that the dimeric association and relative positioning in solution matched better with our crystal structure instead of previously reported structure. Together, structural/biophysical data analysis uphold a tight dimeric structure for SALT protein with one mannose bound to each protein, which remains novel to date, as previous structures indicated one sugar unit sandwiched loosely between two protein chains.
Highlights
Salinity is one of the major abiotic stresses that significantly reduce the yield of rice[1]
Results were supported with the gel filtration profile of the SALT protein which primarily eluted as dimer when referenced to retention time of proteins with known apparent molecular masses (Fig. 2f)
The Jacalin-related lectins have been classified into three main categories based on their oligomeric state
Summary
Salinity is one of the major abiotic stresses that significantly reduce the yield of rice[1]. Among SalTol QTL genes of rice, SalT (GenBank: Z25811.1 Accession No.: Z25811.1) which encodes SALT protein (145 amino acids); a mannose binding lectin is considered crucial in governing salinity tolerance in r ice[12,13]. Many laboratories across the world are engaged in characterization of important mannose binding genes in different plant species and trying to utilize it for crop improvement p rogrammes[15,16,17,19,20]. Till these Man-binding lectins have been reported and characterized from five monocot families including Liliaceae, Amaryllidaceae, Orchidaceae, Alliaceae, and Araceae[21]. The present work delves with the detailed structural characterization of SALT protein in complex with mannose both in solution as well in crystalline state using SAXS data analysis and X-ray crystallography, respectively
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