Mutations in the Carboxyl Terminus of the Agouti Protein Decrease Agouti Inhibition of Ligand Binding to the Melanocortin Receptors
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- 作者：Laura L. Kiefer ; Olivia R. R. Ittoop ; Keith Bunce ; Anne T. Truesdale ; Derril H. Willard ; James S. Nichols ; Steven G. Blanchard ; Kathleen Mountjoy ; Wen-Ji Chen ; and William O. Wilkison
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：February 25, 1997
- 年：1997
- 卷：36
- 期：8
- 页码：2084 - 2090
- 全文大小：241K
- 年卷期：v.36,no.8(February 25, 1997)
- ISSN：1520-4995
文摘
Several mutations that cause ectopic expression of the agouti generesult in obesity,hyperinsulinemia, and yellow coat color. A candidate pathway foragouti induced obesity andhyperinsulinemia is through altered signaling by melanocortinreceptors, as agouti normally regulatescoat coloration through antagonism of melanocortin receptor 1.Furthermore, melanocortin peptides mediatefunctions including steroidogenesis, lipolysis, and thermoregulation.We report apparent inhibitiondissociation constants for mouse and human agouti protein inhibition ofligand binding to the melanocortinreceptors, to determine which of these receptors might be involved inagouti induced diabetes. Thesimilarity in the apparent KI values for agoutiinhibition of ligand binding to the brain melanocortinreceptors3 and 4 (mouse: KI app = 190 ±74 and 54 ± 18 nM; human: KI app= 140 ± 56 and 70 ± 18 nM,respectively) suggests that the MC3-R is a potential candidate for areceptor mediating the effects ofagouti protein overexpression. Agouti residues important formelanocortin receptor inhibition wereidentified through the analysis of deletion constructs andsite-specific variants. Val83 is important forinhibition of binding to MC1-R (KIapp for Val83Ala agouti increased 13-fold relative towild-type protein).Arg85, Pro86, and Pro89 are important for selective inhibition ofbinding between MC1-R and MC3-Rand MC4-R as their apparent KI values areessentially unchanged at MC1-R, while they have increased6-10-fold relative to wild-type protein at MC3-R andMC4-R.