Pex19, a crucial protein, was initially described as an essential peroxisome biogenesis factor. It selectively targets membrane proteins to peroxisomes, playing a vital role in peroxisome-related pathways [2,3,4,7,8]. Given its role in peroxisome biogenesis, genetic models such as gene knockout (KO) or conditional knockout (CKO) mouse models could potentially be valuable for studying its functions.

Non-farnesylated Pex19 can fully restore the metabolic activity of peroxisomes, while farnesylated Pex19 controls lipid metabolism through a peroxisome-independent mechanism by sorting a specific protein subset to lipid droplets (LDs). In the absence of this Pex19-dependent LD proteome, cells accumulate excess triacylglycerols and fail to fully deplete their neutral lipid stores [1]. Pex19 is also involved in the recognition, chaperoning, trafficking, and membrane insertion of Pex11, an abundant peroxisomal membrane protein required for peroxisome division [3]. Additionally, it may play a role in the interaction between flaviviruses (like dengue and Zika virus) and the host, as their capsid proteins bind to Pex19, yet the interaction doesn't target the capsid to peroxisomes [4]. It has been found that viperin, an interferon-stimulated gene product, interacts with Pex19 to mediate peroxisomal augmentation of the innate antiviral response [5]. Pex19 is also involved in importing dually-targeted tail-anchored proteins to both mitochondria and peroxisomes [6]. Moreover, the M2 protein of the influenza A virus interacts with Pex19 to facilitate virus replication by disrupting the function of peroxisome [7]. Pex19 functions as both a chaperone and an import receptor for class 1 peroxisomal membrane proteins [8].

In conclusion, Pex19 is essential for peroxisome biogenesis and has diverse functions in lipid metabolism, protein trafficking to organelles, and the host-virus interaction. Studies on Pex19 using KO or CKO mouse models (if available in the future) could potentially shed more light on its role in diseases related to peroxisome dysfunction, lipid metabolism disorders, and viral infections.