Use of a Tetrapeptide Library to Discover Ligands that Restore Function at a Human Melanocortin-4 Receptor Polymorphism

摘要

The melanocortin system is comprised of G-protein coupled receptors along with a series of endogenous agonists and antagonists and has been identified to be involved in weight control. The endogenous agonists all contain a core tetrapeptide sequence, His-Phe-Arg-Trp, that has been shown to be important for both molecular recognition and molecular stimulation [1]. The melanocortin-4 receptor (MC4R) has been shown to be involved in weight and energy homeostasis, as well as feeding behavior [2,3]. Obesity is a major health concern and its increasing prevalence justifies studies involving the genetic factors influencing it. Up to 6% of morbidly obese humans have a single mutation within the MC4R and studies have indicated that these mutations lead to obesity because of reduced cell surface expression and decreased affinity of the agonists for the receptor [4]. The L106P melanocortin-4 receptor single nucleotide polymorphism has been reported as a heterozygous polymorphism in an obese patient [5]. The L106P mutation is important to investigate because it is putatively located in the binding region for endogenous ligands. Also, the amino acid proline is referred to as a helix breaker and is postulated to distort the normal binding pocket. Endogenous agonists have decreased affinity and efficacy at the L106P, while tetrapeptides were shown to exhibit nM potency [6,7]. Therefore, it was hypothesized that we could screen a synthetic combinatorial tetrapeptide library, in an assay that focuses on this polymorphism in order to identify ligands that may restore functional activity [8].