Temperature-Induced Protein Conformational Changes in Barley Root Plasma Membrane-Enriched Microsomes

Abstract

Temperature and cations modified the reaction of barley (Hordeum vulgare L. cv Conguest) root plasma membrane protein sulfhydryl groups with N-4-(7-diethylamino-4-methylcoumarin-3-yl)-phenyl maleimide (CPM). The pseudo-first-order rate constants for the formation of fluorescent CPM-protein adducts increased as the temperature was raised above 300C, suggesting changes in protein conformation. Monovalent [K(l) It has been demonstrated with animal membrane systems that temperature-induced alterations in the structure of plasma membrane lipids can influence the conformation of membrane-bound proteins (8) often modifying the activity of membrane-bound enzymes (19,21,23). Although there have been investigations of the effect of temperature on the biophysical structure of plant plasma membrane lipids (18), only recently have such studies been extended to the effect of temperature-induced changes in lipid structure on membrane protein conformation and function (1, 2, 5, 13). In the previous reports of this series (1, 5), both EPR' and intrinsic protein fluorescence were used to demonstrate that temperature-induced changes in lipid structure altered the dynamics of the membrane proteins. The temperature-induced, lipidmediated changes in protein conformation coincided with changes in the activity of the plasma membrane-bound ATPase (2).Thermally induced changes in protein conformation may result from the disruption of the chemical bonds involved in the maintenance of protein structure (23). Levitt (1 1, 12) proposed that plant exposure to freezing, chilling, and high temperatures could cause metabolic dysfunctions, as a result 'Abbreviations: EPR, electron paramagnetic resonance; RuBPCase, ribulose bisphosphate carboxylase/oxygenase; CPM, N-4-(7-diethylamino-4-methylcoumarin-3-yl)-phenyl maleimide; DACM, N-(7-dimethylamino-4-coumarinyl)-maleimide; DPH, diphenylhexatriene.of the modification of protein intra-and intermolecular sulfhydryl bonds (SH-hypothesis). According to the SH-hypothesis, a variety of environmental stresses may cause membrane damage by inducing the aggregation of membrane proteins. Temperature extremes could result in altered protein conformation which promotes aggregation through the generation intermolecular bonds. Although enhanced hydrophobic interactions were not excluded, Levitt (1 1, 12) emphasized the role of intermolecular disulfide linkages in the formation of the protein aggregates. Furthermore, any stress-induced increase in the exposure of protein sulfhydryl groups might also damage membrane proteins by allowing the binding of heavy metal cations (11). It has been suggested that the observed increases in plant cellular nonprotein sulfhydrylcontaining compounds, usually glutathione, induced by low temperatures could prevent stress-induced protein damage (7,11,12).Other than the increased glutathione levels, there is little direct evidence for Levitt's SH-hypothesis. The cold temperature inactivation of the cytosolic enzyme RuBPCase from tobacco resulted in increased exposure of prote...

Effect of salinity and arbuscular mycorrhizal fungi on growth and some physiological parameters ofCitrus jambheri

“…Electrolyte leakage increased as salinity stress levels increased, indicating that salinity leads to disturbance in permeability and stability of the cellular membranes, as well as lipid peroxidation (Tajdoost et al 2007). Abiotic stresses lead to disturbance in the association between membrane lipids and proteins, which decreases enzyme activity and transport capacity of the bilayer (Caldwell & Whitman 1987). Mycorrhizal plants (except plants inoculated with G. etunicatum at soil salinity level of 4 dS m −1 ) had lower electrolyte leakage than NM control plants at different levels of soil salinity.…”

Effects of drought on photosynthetic characteristics of flag leaves of a newly-developed super-high-yield rice hybrid

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Drought Stress Syndrome in Wheat Is Provoked by Ethylene Evolution Imbalance and Reversed by Rewatering, Aminoethoxyvinylglycine, or Sodium Benzoate

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