ABSTRACT
The observation that a nucleotide, guanosine triphosphate, is required for a hormone to activate an enzyme through adenylyl cyclase led to the identification of the significance of G proteins in cellular signaling. Binding of a cell surface receptor by an external ligand triggers a cascade of cellular events via transmembrane signaling mechanisms. Most of the G-protein subunits, cDNAs and genes, have been cloned or the proteins purified in the native state. Lipopolysaccharide, a cell wall component of gram-negative bacteria, produces a plethora of effects in vitro and in vivo. The response of cells or animals changes dramatically when preexposed to low concentrations or doses of Lipopolysaccharide (LPS) before stimulation in vitro with higher concentrations or in vivo with lethal LPS doses. While much progress has been made with regard to understanding LPS-mediated cellular signal-transduction mechanisms, there is still much to learn.
