Structural Insight into G-Protein Coupled Receptor Binding by Apelin

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• 作者：David N. Langelaan ; E. Meghan Bebbington ; Tyler Reddy ; Jan K. Rainey
• 刊名：Biochemistry
• 出版年：2009
• 出版时间：January 27, 2009
• 年：2009
• 卷：48
• 期：3
• 页码：537-548
• 全文大小：492K
• 年卷期：v.48,no.3(January 27, 2009)
• ISSN：1520-4995

文摘

Apelin peptides are the cognate ligands for the G-protein coupled receptor APJ, with functions in the cardiovascular and central nervous systems, in glucose metabolism and as a human immunodeficiency virus (HIV-1) coreceptor. Apelin is found in 13−36 residue forms in vivo. The structures of five isoforms of apelin at physiological versus low (5−6 °C) temperature are compared here using circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy, demonstrating increased structure at low temperature. Far-ultraviolet (UV) CD spectra are predominantly random coil for apelin isoforms, but are convoluted by unusual bands from the C-terminal phenylalanine side chain. These bands, assigned using F13A-apelin-13, are accentuated at 5 °C and imply conformational restriction. At 35 °C, the R6−L9 region of apelin-17 is well structured, consistent with previous mutagenesis results showing necessity of this segment for apelin−APJ binding and activation. At 5 °C, R6−L9 retains its structuring while the functionally critical C-terminal G13−F17 region also becomes highly structured. Type IV β-turns and some polyproline-II structure alongside F17 side chain motional reduction correlate well with CD spectral properties. Cis−trans peptide bond isomerization at P14 and P16 produces two sequentially assignable conformers (both trans:both cis 4:1) alongside less populated conformers. Chemical shift assignment of apelin-12, -13 and pyroglutamate-apelin-13 implies highly similar structuring and the same isomerization at the C-terminus. Based on the apelin-17 structure, a two-step binding and activation mechanism is hypothesized.