Functional characterization of GmITPK (myo-inositol: 1, 3, 4 tris phosphate 5/6 kinase) isoforms-'so different yet so similar'

摘要

The biochemical basis behind the preferential presence and action of GmITPKs (myo-inositol-1, 3, 4 tris phosphate 5/6 kinases) in regulating the phosphorous flux towards phytate synthesis in soybean is an important, still unresolved question. In this study, context specific expression of GmITPKs in developing seeds was analysed, which found to be maximum at early stages (0-4 mm); while isozyme specificity was observed with varied dynamics till maturity. It is commonly believed that similarity at sequence level will infer similarity in structure as well, but the robust correlation between sequence and structure has not yet been proved. Hence full length coding sequences of GmITPKs were cloned and their sequence comparison revealed a low identity score of about 50% among the isoforms. Creative computational tools were employed to predict and comprehend the structural attributes and to explore the inverse correlation between the structural and sequence similarities of GmITPKs. Homology modeling of GmITPKs, their refinement and superposition validated the functional isoformic nature, with 92-97% similarity in spatial configuration. Ligand docking and energy computations showed ADP, IP6 and IP5 as possible ligands, and interactions were studied using docking and simulation. The homology models of GmITPKs were used as the starting point for nanosecond-duration molecular dynamics and were found to be stable during 20 ns simulation period. Existence of situation-specific functional basis for this isoform multiplicity, at structural and expression levels revealed to be a preferred regulatory mechanism to adapt to the metabolic fluctuations in inositol pathway during seed development.