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β-Arrestins (βarrs) are functionally versatile proteins that play critical roles in the G-protein-coupled receptor (GPCR) signaling pathways. While the classical theory of GPCR-mediated βarr activation centers around the formation of a stable complex between βarr and the phosphorylated receptor tail, emerging evidences highlight the indispensable contribution from membrane lipids for many receptors. Due to the intrinsic complexity of βarr conformational dynamics, detailed molecular mechanisms of its activation by different binding partners remain elusive. Herein we present a comprehensive study of the structural changes of βarr1 in critical structural regions during activation using19F NMR method. We demonstrate that phosphopeptides derived from different classes of GPCRs show distinct abilities in inducing βarr1 activation. We further show that the membrane phosphoinositide PIP2independently modulates βarr1 conformational dynamics without displacing its autoinhibitory carboxyl tail, leading to a distinct partially activated state. Our results delineate two activation mechanisms of βarr1 by different binding partners, uncovering a highly multifaceted conformational energy landscape for this protein family.

For investigating the flow phenomena in the stall process of a counter-rotating compressor (CRC), static and dynamic experiment have been carried out on a low speed counter-rotating compressor. Seven high response pressure sensors were mounted at the leading edge of rotor 1(R1) and rotor 2(R2) as well as at the outlet of R2 blade tip and root. Wavelet analysis and FFT transform was introduced to the post processing progress. According to the experimental results, the stall inception was found in the tip region of the second rotor. The rotating speed of stall cell in the compressor is about 35% of the rotor speed.

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