sentence: This review summarizes the current knowledge on the biology of FFAR1 ( GPR40 ) , FFAR2 ( GPR43 ) , FFAR3 ( GPR41 ) , FFAR4 ( GPR120 ) , and GPR84 , including structural aspects of FFAR1 , and discusses the molecular pharmacology of FFAR allosteric ligands as well as the opportunities and challenges in research from the perspective of drug discovery .