Mass spectrometry analysis of protein/peptide S-palmitoylation

The dynamic S-palmitoylation regulates many intracellular events, including protein trafficking, anchoring, targeting, and protein-protein interactions. Direct detection of S-palmitoylation by conventional liquid chromatography-mass spectrometry (LC-MS) methods is challenging because of the tendency of palmitoyl loss during sample preparation and gas phase fragmentation. Additionally, the high hydrophobicity of the palmitoyl group can prevent proper elution of palmitoyl peptides from the commonly used C18 column. Here, we developed a comprehensive strategy tailored for S-palmitoyl detection using three palmitoyl peptide standards. We found that S-palmitoylation was largely preserved in neutral Tris buffer with tris(2-carboxyethyl)phosphine as the reducing agent and that various fragmentation methods provided complementary information for palmitoyl localization. Moreover, S-palmitoyl peptides were efficiently analyzed using a C4 column and the derivatization of free cysteine with a hydrophobic tag allowed relative quantification of palmitoyl peptides and their unmodified counterparts. We further discovered potential complications to S-palmitoylation analysis caused by the use of ProteaseMAXTM, an MS-compatible detergent. The hydrophobic degradation products of ProteaseMAXTM reacted with the free cysteine thiols, generating artifacts that mimic S-acylation and hydroxyfarnesylation. Another MS-compatible detergent, RapiGestTM, did not produce such artifacts, and showed the ability to stabilize S-palmitoylation by preventing thioester hydrolysis and dithiothreitol-induced thioester cleavage. Moreover, we found that the palmitoyl peptide GCpalmLGNAK could undergo intermolecular palmitoyl migration from the cysteine to the peptide N-terminus or the lysine side chain during sample preparation, and this could lead to false discovery of N-palmitoylation. RapiGestTM inhibited such migration, and is thus recommended for S-palmitoyl sample preparation. We then applied the established method to analyze the regulator of G-protein signaling 4 (RGS4) which had been reported to undergo S-palmitoylation by radioactive labeling. It had also been reported that the S-palmitoylation state of RGS4 affects its GTPase activity. With LC-MS/MS analysis, we found that the addition of palmitate to the cell culture medium in metabolic labeling experiments could boost the level of S-palmitoylation, leading to false discovery of new S-palmitoylation site(s). We also noted discrepancies between the S-palmitoylation sites identified by radioactive labeling and by LC-MS/MS analysis. Further studies are needed to evaluate the reliability of S-palmitoyl detection by these two methods

ROLES OF ABCG5 ABCG8 CHOLESTEROL TRANSPORTER IN LIPID HOMEOSTASIS

The ABCG5 ABCG8 (G5G8) sterol transporter promotes cholesterol secretion into bile and opposes dietary sterol absorption in the small intestine. An emerging body of literature suggests that G5G8 links sterol flux to various risk factors for metabolic syndrome (MetS) and nonalcoholic fatty liver disease (NAFLD). Therapeutic approaches that accelerate G5G8 activity may augment reverse cholesterol transport (RCT) and provide beneficial effects in the prevention and treatment of cardiovascular and liver disease. Mice lacking leptin (ob/ob) or its receptor (db/db) are obese, insulin resistant in part due to the reduced levels of hepatic G5G8 and biliary cholesterol. The underlying mechanisms responsible for the reduced G5G8 protein expression in these mice may provide a clue to the drug development for this target. My studies show that neither acute leptin replacement nor liver-specific deletion of leptin receptor alters G5G8 abundance or biliary cholesterol. Similarly, hepatic vagotomy has no effect on G5G8 expression. Conversely, expression of the ER chaperone, GRP78, rescues G5G8 in db/db mice. Previous studies suggest an interdependent relationship between liver and intestine for cholesterol elimination. A combination therapy that increases G5G8-mediated biliary cholesterol secretion and simultaneously reduces intestinal absorption is likely to act additively in cholesterol elimination. My studies show that treatment with ursodiol (Urso) increases hepatic G5G8 protein and both biliary and fecal sterols in a dose-dependent manner. Ezetimibe (EZ), a potent inhibitor of intestinal cholesterol absorption, produces an additive and dose-dependent increase in fecal sterol excretion in the presence of Urso. However, the stimulatory effects of both Urso and Urso-EZ are not G5G8-dependent. Beyond increasing G5G8 protein expression and biliary cholesterol secretion, my studies also show that Urso stimulates ileal FGF15 expression in mice. Our data of the stimulated ileal FGF15 expression in LIRKO and reduced hepatic G5G8 protein levels in Atsb KO mice both indicate the previous unrecognized role of FGF15/19 in the regulation of G5G8 and its activity. Indeed, this is subsequently confirmed by our results from the direct test of recombinant human FGF19 on G5G8. Thus, FGF15/19 may provide an alternative strategy in drug development to target G5G8 activity and accelerate cholesterol elimination

Vibration and stability of internally damped rotating composite Timoshenko shaft

The mechanical model for the dynamic behavior of an internally damped rotating composite shaft is derived using a refined variational asymptotic method and the principle of virtual work. The composite shaft is considered as an anisotropic thin-walled Timoshenko beam. The internal damping of composite shaft is modelled by adopting the multi-scale damping analysis method. Galerkin’s method is employed to discretize and solve the equations of motion. The effect of design parameters including fiber orientation, length aspect ratio, stacking sequences and boundary conditions on the free vibration and stability of composite shaft is investigated

Energy Use and CO2 Emission Inventories in the Four Municipalities of China

AbstractEmission inventories are important tools for monitoring air quality and assisting the policies in urban areas. This paper estimates Beijing, Shanghai, Tianjin, and Chongqing's CO2 emissions of energy consumption and carbon intensity of the economic activities in 1990, 1995, 2000 and 2004-2007 based on the method recommended by IPCC. The results show that the coal combustion is the leading cause of total CO2 emission from energy consumption, occupied over 60% of total CO2 emission of fuels. But the share of CO2 emission from coal is descending gradually because of energy consumption restructuring. In addition, the four mega-cities’ carbon intensity of the economic activities, which is the low Carbon Economy index, is improving persistently. These results imply that China's CO2 emission in the future may not become as high as expected but improve with time

Banks’ maturity mismatch, financial stability, and macroeconomic dynamics

The average maturity of total bank assets has been rising sharply following the 4-trillion-yuan stimulus package proposed by the Chinese government in 2009. This paper investigates the macroeconomic implications of maturity mismatch problem using the Chinese data over the period 2007Q1–2019Q4. We extend the New-Keynesian DSGE framework from several dimensions: (i) financial frictions between banks and households; (ii) multi-period loan contracts; (iii) dynamic differential reserve requirement as a macroprudential regulation tool. After estimating the model with Chinese data, the simulation results indicate that the sluggish adjustment of financing cost caused by maturity mismatch will attenuate the real sector fluctuation, however, the feedback effects will amplify the responses of the banking sector. Meanwhile, a severe maturity mismatch will dampen the effect of the required reserve rate as a tool to keep financial stability when confronted with productivity shock

Channel Adaptive DL based Joint Source-Channel Coding without A Prior Knowledge

Significant progress has been made in wireless Joint Source-Channel Coding (JSCC) using deep learning techniques. The latest DL-based image JSCC methods have demonstrated exceptional performance across various signal-to-noise ratio (SNR) levels during transmission, while also avoiding cliff effects. However, current channel adaptive JSCC methods rely heavily on channel prior knowledge, which can lead to performance degradation in practical applications due to channel mismatch effects. This paper proposes a novel approach for image transmission, called Channel Blind Joint Source-Channel Coding (CBJSCC). CBJSCC utilizes Deep Learning techniques to achieve exceptional performance across various signal-to-noise ratio (SNR) levels during transmission, without relying on channel prior information. We have designed an Inverted Residual Attention Bottleneck (IRAB) module for the model, which can effectively reduce the number of parameters while expanding the receptive field. In addition, we have incorporated a convolution and self-attention mixed encoding module to establish long-range dependency relationships between channel symbols. Our experiments have shown that CBJSCC outperforms existing channel adaptive DL-based JSCC methods that rely on feedback information. Furthermore, we found that channel estimation does not significantly benefit CBJSCC, which provides insights for the future design of DL-based JSCC methods. The reliability of the proposed method is further demonstrated through an analysis of the model bottleneck and its adaptability to different domains, as shown by our experiments