TLQP-21, a VGF-encoded peptide is emerging as a novel target for obesity-associated disorders. TLQP-21 is found in the sympathetic nerve terminals in the adipose tissue and targets the G-protein-coupled receptor complement-3a receptor1 (C3aR1). The mechanisms of TLQP-21-induced receptor activation remain unexplored. Here, we report that TLQP-21 is intrinsically disordered and undergoes a disorder-to-order transition, adopting an α-helical conformation upon targeting cells expressing the C3aR1. We determined that the hot spots for TLQP-21 are located at the C terminus, with mutations in the last four amino acids progressively reducing the bioactivity and, a single site mutation (R21A) or C-terminal amidation abolishing its function completely. Additionally, the human TLQP-21 sequence carrying a S20A substitution activates the human C3aR1 receptor with lower potency compared to the rodent sequence. These studies reveal the mechanism of action of TLQP-21 and provide molecular templates for designing agonists and antagonists to modulate C3aR1 functions.
Bibliographical noteFunding Information:
Supported by the Minnesota Partnership for Biotechnology and Medical Genomic, Decade of Discovery in Diabetes Grant (to A.B.), NIH/DK102496 (to A.B.), NIH R01DE021996 and NIH R21DA025170 (to L.V.), and the NIMH Psychoactive Drug Screening Program (to B.L.R. and M.F.S.). NMR experiments were carried out at the Minnesota NMR Center. 3T3L1 cells were provided by The Molecular & Cellular Basis of Obesity Core, Minnesota Obesity Center (P30 DK050456). We thank D. Piomelli, G. Bottegoni, W. Rocchia, A. Lodola, and M. Mor for important suggestions in various stages of the study, and I. Ninkovich, P. Petrocchi, and M. Razzoli for technical help.
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