PLIN4

Perilipin 4 is a protein that in humans is encoded by the PLIN4 gene.

Structure
The protein encoded by the PLIN4 gene is active as a monomer, meaning there is only one peptide chain involved in its assembly. It is 247 amino acids long and weighs approximately 27.57 KDa.

Function
PLIN4 is a member of the perilipin family, a group of proteins that coat lipid droplets in adipocytes, the adipose tissue cells that are responsible for storing fat. Perilipin acts as a protective coating from the body’s natural lipases, such as hormone-sensitive lipase, which break triglycerides into glycerol and free fatty acids for use in metabolism, a process called lipolysis. In humans, perilipin is expressed as 5 different isoforms; it is currently understood that the level of expression for each isoform is dependent on factors such as sex, body mass index, and level of endurance exercise.

PLIN4 is hyperphosphorylated by PKA following β-adrenergic receptor activation.Phosphorylated perilipin changes conformation, exposing the stored lipids to hormone-sensitive lipase-mediated lipolysis. Although PKA also phosphorylates hormone-sensitive lipase, which can increase its activity, the more than 50-fold increase in fat mobilization (triggered by epinephrine) is primarily due to perilipin phosphorylation.

Clinical significance
The proteins in the Perilipin family are crucial regulators of lipid storage. PLIN4 expression is elevated in obese animals and humans. Perilipin-null mice eat more food than wild-type mice, but gain 1/3 less fat than wild-type mice on the same diet; perilipin-null mice are thinner, with more lean muscle mass. Perilipin-null mice also exhibit enhanced leptin production and a greater tendency to develop insulin resistance than wild-type mice.

The PLIN4 gene, along with PLIN2, PLIN3, and PLIN5, have been associated with variance in body-weight regulation and may be a genetic influence on obesity risk in humans.

Interactions
PLIN4 has been shown to interact with Caspase 8 and Ubiquitin C.