Proteomic identification of binding partners for the brain metabolite lanthionine ketimine (LK) and documentation of LK effects on microglia and motoneuron cell cultures.

Lanthionine ketimine (LK) represents a poorly understood class of thioethers present in mammalian CNS. Previous work has indicated high-affinity interaction of LK with synaptosomal membrane protein(s), but neither LK binding partners nor specific bioactivities have been reported. In this study, LK was chemically synthesized and used as an affinity agent to capture binding partners from mammalian brain lysate. Liquid chromatography with electrospray ionization-mass spectrometry of electrophoretically separated, LK-bound proteins identified polypeptides implicated in axon remodeling or vesicle trafficking and diseases including Alzheimer's disease and schizophrenia: collapsin response mediator protein-2/dihydropyrimidinase-like protein-2 (CRMP2/DRP2/DPYSL2), myelin basic protein, and syntaxin-binding protein-1 (STXBP1/Munc-18). Also identified was the recently discovered glutathione-binding protein lanthionine synthetase-like protein-1. Functional consequences of LK:CRMP2 interactions were probed through immunoprecipitation studies using brain lysate wherein LK was found to increase CRMP2 coprecipitation with its partner neurofibromin-1 but decreased CRMP2 coprecipitation with beta-tubulin. Functional studies of NSC-34 motor neuron-like cells indicated that a cell-permeable LK-ester, LKE, was nontoxic and protective against oxidative challenge with H(2)O(2). LKE-treated NSC-34 cells significantly increased neurite number and length in a serum concentration-dependent manner, consistent with a CRMP2 interaction. Finally, LKE antagonized the activation of EOC-20 microglia by inflammogens. The results are discussed with reference to possible biochemical origins, paracrine functions, neurological significance, and pharmacological potential of lanthionyl compounds.