The cardioprotective function of high-density lipoprotein (HDL) is largely attributed to its ability to facilitate transport of cholesterol from peripheral tissues to the liver. However, HDL may become dysfunctional through oxidative modification, impairing cellular cholesterol efflux. Here we report a refined molecular model of nascent discoidal HDL, determined using hydrogen-deuterium exchange mass spectrometry. The model reveals two apolipoprotein A1 (apoA1) molecules arranged in an antiparallel double-belt structure, with residues 159-180 of each apoA1 forming a protruding solvent-exposed loop. We further show that this loop, including Tyr166, a preferred target for site-specific oxidative modification within atheroma, directly interacts with and activates lecithin cholesterol acyl transferase. These studies identify previously uncharacterized structural features of apoA1 in discoidal HDL that are crucial for particle maturation, and elucidate a structural and molecular mechanism for generating a dysfunctional form of HDL in atherosclerosis.

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Myeloperoxidase (MPO) and paraoxonase 1 (PON1) are high-density lipoprotein-associated (HDL-associated) proteins mechanistically linked to inflammation, oxidant stress, and atherosclerosis. MPO is a source of ROS during inflammation and can oxidize apolipoprotein A1 (APOA1) of HDL, impairing its atheroprotective functions. In contrast, PON1 fosters systemic antioxidant effects and promotes some of the atheroprotective properties attributed to HDL. Here, we demonstrate that MPO, PON1, and HDL bind to one another, forming a ternary complex, wherein PON1 partially inhibits MPO activity, while MPO inactivates PON1. MPO oxidizes PON1 on tyrosine 71 (Tyr 71 ), a modified residue found in human atheroma that is critical for HDL binding and PON1 function. Acute inflammation model studies with transgenic and knockout mice for either PON1 or MPO confirmed that MPO and PON1 reciprocally modulate each other's function in vivo. Further structure and function studies identified critical contact sites between APOA1 within HDL, PON1, and MPO, and proteomics studies of HDL recovered from acute coronary syndrome (ACS) subjects revealed enhanced chlorotyrosine content, site-specific PON1 methionine oxidation, and reduced PON1 activity. HDL thus serves as a scaffold upon which MPO and PON1 interact during inflammation, whereupon PON1 binding partially inhibits MPO activity, and MPO promotes site-specific oxidative modification and impairment of PON1 and APOA1 function.

SummaryBackgroundFaecal microbiota transplantation is an experimental approach for the treatment of patients with ulcerative colitis. Although there is growing evidence that faecal microbiota transplantation is effective in this disease, factors affecting its response are unknown.AimsTo establish a faecal microbiota transplantation treatment protocol in ulcerative colitis patients, and to investigate which patient or donor factors are responsible for the treatment success.MethodsThis is an open controlled trial of repeated faecal microbiota transplantation after antibiotic pre‐treatment (FMT‐group, n = 17) vs antibiotic pre‐treatment only (AB‐group, n = 10) in 27 therapy refractory ulcerative colitis patients over 90 days. Faecal samples of donors and patients were analysed by 16SrRNA gene‐based microbiota analysis.ResultsIn the FMT‐group, 10/17 (59%) of patients showed a response and 4/17 (24%) a remission to faecal microbiota transplantation. Response to faecal microbiota transplantation was mainly influenced by the taxonomic composition of the donor's microbiota. Stool of donors with a high bacterial richness (observed species remission 946 ± 93 vs no response 797 ± 181 at 15367 rps) and a high relative abundance of Akkermansia muciniphila (3.3 ± 3.1% vs 0.1 ± 0.2%), unclassified Ruminococcaceae (13.8 ± 5.0% vs 7.5 ± 3.7%), and Ruminococcus spp. (4.9 ± 3.5% vs 1.0 ± 0.7%) were more likely to induce remission. In contrast antibiotic treatment alone (AB‐group) was poorly tolerated, probably because of a sustained decrease of intestinal microbial richness.ConclusionsThe taxonomic composition of the donor's intestinal microbiota is a major factor influencing the efficacy of faecal microbiota transplantation in ulcerative colitis patients. The design of specific microbial preparation might lead to new treatments for ulcerative colitis.

High density lipoprotein (HDL), the carrier of so-called "good" cholesterol, serves as the major athero-protective lipoprotein and has emerged as a key therapeutic target for cardiovascular disease. We applied small angle neutron scattering (SANS) with contrast variation and selective isotopic deuteration to the study of nascent HDL to obtain the low resolution structure in solution of the overall time-averaged conformation of apolipoprotein AI (apoA-I) versus the lipid (acyl chain) core of the particle. Remarkably, apoA-I is observed to possess an open helical shape that wraps around a central ellipsoidal lipid phase. Using the low resolution SANS shapes of the protein and lipid core as scaffolding, an all-atom computational model for the protein and lipid components of nascent HDL was developed by integrating complementary structural data from hydrogen/deuterium exchange mass spectrometry and previously published constraints from multiple biophysical techniques. Both SANS data and the new computational model, the double superhelix model, suggest an unexpected structural arrangement of protein and lipids of nascent HDL, an anti-parallel double superhelix wrapped around an ellipsoidal lipid phase. The protein and lipid organization in nascent HDL envisages a potential generalized mechanism for lipoprotein biogenesis and remodeling, biological processes critical to sterol and lipid transport, organismal energy metabolism, and innate immunity. High density lipoprotein (HDL)2 functions in removal of cholesterol from peripheral tissues, such as within the artery wall, for delivery to the liver and ultimate excretion as biliary cholesterol within the intestinal lumen, a process called reverse cholesterol transport (1, 2). Plasma levels of HDL cholesterol and apolipoprotein AI (apoA-I), the major protein component of HDL, are inversely related to the risk of developing coronary artery disease (3-5). Moreover, genetic alterations that induce changes in apoA-I levels in both animals and humans alter susceptibility for development of atherosclerotic heart disease (3-6). Thus, numerous interventions aimed at enhancing reverse cholesterol transport are being examined as potential novel therapeutic interventions for the prevention and treatment of cardiovascular disease (7,8). Examples include methods for generating new HDL particles through enhanced production or delivery of either intact apoA-I (9, 10) or peptide mimetics of apoA-I (11), as well as modulating interactions between nascent HDL and proteins involved in HDL particle maturation and remodeling for potential therapeutic benefit (12-14). Structural elucidation often serves as the "Rosetta Stone" for enhanced understanding of function. It is thus remarkable that despite its importance to numerous biological and biomedical functions and its current prominent role as a target for therapeutic interventions, to date, the structures of neither the protein nor lipid components of nascent HDL have been directly visualized, and the high resolution structure of the particl...