Directed evolution of recombinant serum paraoxonase (PON) variants

Extract: Owing to their detoxifying functions, and roles in drug metabolism as well as the prevention of atherosclerosis, mammalian or serum paraoxonases (PONs) are an intriguing subject of research and a prime therapeutic and engineering target. Initially identified in mammals, PON and PON-related genes have now been found in fowls, zebra fish, and even in invertebrates such as C. elegans. The more closely-related PON genes are divided into three classes or sub-families: PON1, PON2 and PON3, that share 60-70% sequence identity. PONs are calcium-dependent hydrolases that catalyze the hydrolysis of a broad range of esters and lactones. PON1, which is by far the most investigated member of this family, also catalyzes, albeit at much lower rates, the hydrolysis and thereby inactivation of various organophosphates (OPs), including the nerve agents sarin and soman. PON1 is also involved in drug metabolism and is used for drug inactivation. In recent years, it has become apparent that PONs also play an important role in the prevention of atherosclerosis. The levels of PON1 in the blood and its catalytic proficiency appear to have a major impact both on the individual's susceptibility to pollutants and insecticides, and to atherosclerosis. Furthermore, mice lacking the PON1 gene are highly susceptible to atherosclerosis and to OP poisoning. PON1 and PON3 reside in the high-density lipoprotein cholesterol-carrying particles known as HDL ("good cholesterol"). HDL has two key roles: mediation of cholesterol efflux, e.g., from macrophage foam cells in atherosclerotic lesions, and limitation of lipid oxidation in LDL. PONs have been implicated in both activities.