Abstract
AbstractThe significance of winter cold in the termination of diapause was investigated with regards to TIME and PIN in eggs of the silkworm Bombyx mori. TIME (time interval measuring enzyme) is an ATPase that can measure time intervals by exhibiting a transitory burst of activation of the enzyme in accordance with diapause development, which requires cold for resumption of embryonic development in the silkworm. The possible timer function of TIME comprises a built‐in mechanism in the protein structure. TIME is a metallo‐glycoprotein consisting of 156 amino acid residues with a unique sequence in the N‐terminal region to which a sugar chain is attached. PIN (peptidyl inhibitory needle) inhibits the ATPase activity of TIME. PIN is not a simple enzyme inhibitor, but holds the timer by forming a time‐regulatory complex with TIME. The carbohydrate moiety of TIME is essential for the assembly of a high‐affinity PIN‐binding site within the timer motif of the TIME structure. The binding interaction between TIME and PIN was much tighter (nearly 1000 times) at 25°C than that at 4°C, as measured by fluorescence polarization. Because the logEC50 at 4°C was approximately 7 nmol/L, PIN must dissociate from TIME at the physiological concentration of TIME in eggs in the winter cold. Based on the results of our study, we propose that the dissociation of the TIME–PIN complex in the winter cold cues a series of conformational changes of TIME, ultimately reaching the active form of ATPase which in turn causes the completion of diapause development and initiates new developmental programs.
Published Version
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