Negatively regulates the expression of the gbsAB and opuB operons. Required to control expression of these genes in response to choline availability. Also required to down-regulate glycine betaine production once cellular adjustment to high osmolarity has been achieved. Intracellular choline sensor. Binding to choline induces conformational changes and relieves the repressing effects of GbsR on expression. Belongs to the GbsR family.