title: Agouti-related protein segments outside of the receptor binding core are required for enhanced short- and long-term feeding stimulation.
abstract: The agouti-related protein (AgRP) plays a central role in energy balance by reducing signaling through the hypothalamic melanocortin receptors (McRs) 3 and 4, in turn stimulating feeding and decreasing energy expenditure. Mature AgRP(83-132), produced by endoproteolytic processing, contains a central region that folds as an inhibitor cystine knot (ICK) stabilized by a network of disulfide bonds; this domain alone carries the molecular features for high affinity McR binding and inverse agonism. Outside of the ICK domain are two polypeptide segments, an N-terminal extension and a C-terminal loop, both completely conserved but of unknown function. Here we examine the physiological roles of these non-ICK segments by developing a panel of modified AgRPs that were administered to rats through intracerebroventricular (ICV) injection. Analysis of food consumption demonstrates that basic (positively charged) residues are essential for potent short- and long-term AgRP stimulated feeding. Moreover, we demonstrate an approximate linear relationship between protein charge density and 24  h food intake. Next, we developed artificial AgRP(83-132) analogues with increased positive charge and found that these species were substantially more potent than wild type. A single dose of one protein, designated AgRP-4K, results in enhanced feeding for well over a week and weight gain that is nearly double that of AgRP(83-132). These studies suggest new strategies for the development of potent orexigenic species and may serve as leads for the development of therapeutics for treating wasting conditions such as cachexia.
authors: Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, United States.
authors: Michael E
authors: ME
authors: Madonna
authors: Jennifer
authors: J
authors: Schurdak
authors: Ying-Kui
authors: YK
authors: Yang
authors: Stephen
authors: S
authors: Benoit
authors: Glenn L
authors: GL
authors: Millhauser
mesh_terms: D054369:Agouti-Related Protein / Q000008:administration & dosage / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D002100:Cachexia / Q000188:drug therapy; D004326:Drinking / Q000187:drug effects; D005247:Feeding Behavior / Q000187:drug effects*; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D016415:Sequence Alignment
chemical_list: D054369:Agouti-Related Protein