Thermodynamic insights into an interaction between ACYL-CoA–BINDING PROTEIN2 and LYSOPHOSPHOLIPASE2 in Arabidopsis

Abstract

Edited by Joseph M. Jez Lysophospholipids (LPLs) are important lipid-signaling molecules in plants, of which lysophosphatidylcholine (lysoPC) is one of the most well-characterized LPLs, having important roles in plant stress responses. It is broken down by lysophospholipases, but the molecular mechanism involved in lysoPC degradation is unclear. Recombinant Arabidopsis thaliana ACYL-CoA-BINDING PROTEIN2 (AtACBP2) has been reported to bind lysoPC via its acyl-CoA-binding domain and also LYSOPHOSPHOLIPASE 2 (AtLYSOPL2) via its ankyrin repeats in vitro. To investigate the interactions of AtACBP2 with AtLYSOPL2 and lysoPC in more detail, we conducted isothermal titration calorimetry with AtACBP2 70-354 , an AtACBP2 derivative consisting of amino acids 70-354, containing both the acyl-CoA-binding domain and ankyrin repeats. We observed that the interactions of AtACBP2 70-354 with AtLYSOPL2 and lysoPC were both endothermic, favored by solvation entropy and opposed by enthalpy, with dissociation constants in the micromolar range. Of note, three AtLYSOPL2 catalytic triad mutant proteins (S147A, D268A, and H298A) bound lysoPC only weakly, with an exothermic burst and dissociation constants in the millimolar range. Furthermore, the binding affinity of lysoPC-premixed AtACBP2 70-354 to AtLYSOPL2 was 10-fold higher than that of AtACBP2 70-354 alone to AtLY-SOPL2. We conclude that AtACBP2 may play a role in facilitating a direct interaction between AtLYSOPL2 and lysoPC. Our results suggest that AtACBP2 70-354 probably binds to lysoPC through a hydrophobic interface that enhances a hydrotropic interaction of AtACBP2 70-354 with AtLYSOPL2 and thereby facilitates AtLYSOPL2's lysophospholipase function. Phospholipids are crucial components of many biological membranes (1). Lysophospholipids (LPLs) 2 and free fatty acids are produced through the removal of an O-acyl chain (sn-1/ sn-2) from phospholipids by phospholipase hydrolysis (2). LPLs are believed to be critical lipid-signaling molecules in cellular membranes (3). Plant LPLs normally exist in low amounts but can be elevated by environmental stimuli, such as low temperature and pathogen stress (4, 5). One of the most well-characterized LPLs is lysophosphatidylcholine (lysoPC) (6, 7). LysoPC has been reported to enhance pathogen susceptibility in tobacco plants via signaling pathways associated with the accumulation of reactive oxygen species and ethylene (8). As membrane-derived signaling molecules in eukaryotes, LPLs perform various biological functions through activating distinct signal transduction pathways (6, 9). LysoPC activates human T lymphocytes (10), up-regulates the expression of P-selectin in mammalian platelets and endothelial cells (11), and promotes nerve growth factor-induced signals in rat pheochromocytoma PC12 cells and neurotrophin-like activity in cerebellar granule neurons and PC12 cells (12). In mammalian cells, LPL signaling is supported by G protein-coupled plasma membrane receptors (13-15). Lysophospholipases belong to a family of hydrolases that hydr...

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