PEX14 binding to Arabidopsis PEX5 has differential effects on PTS1 and PTS2 cargo occupancy of the receptor

PEX5 acts as a cycling receptor for import of PTS1 proteins into peroxisomes and as a co-receptor for PEX7, the PTS2 receptor, but the mechanism of cargo unloading has remained obscure. Using recombinant protein domains we show PEX5 binding to the PEX14N-terminal domain (PEX14N) has no effect on the affinity of PEX5 for a PTS1 containing peptide. PEX5 can form a complex containing both recombinant PTS1 cargo and endogenous PEX7-thiolase simultaneously but isolation of the complex via the PEX14 construct resulted in an absence of thiolase, suggesting a possible role for PEX14 in the unloading of PTS2 cargos

Peroxisome protein import: a complex journey.

The import of proteins into peroxisomes possesses many unusual features such as the ability to import folded proteins, and a surprising diversity of targeting signals with differing affinities that can be recognised by the same receptor. As understanding of the structure and function of many components of the protein import machinery has grown, an increasingly complex network of factors affecting each step of the import pathway has emerged. Structural studies have revealed the presence of additional interactions between cargo proteins and the PEX5 receptor that affect import potential, with a subtle network of cargo-induced conformational changes in PEX5 being involved in the import process. Biochemical studies have also indicated an interdependence of receptor-cargo import with release of unloaded receptor from the peroxisome. Here we provide an update on recent literature concerning mechanisms of protein import into peroxisomes

Antibody prevalence after three or more COVID-19 vaccine doses in individuals who are immunosuppressed in the UK: a cross-sectional study from MELODY

SummaryBackground In the UK, additional COVID-19 vaccine booster doses and treatments are offered to people who are immunosuppressed to protect against severe COVID-19, but how best to choose the individuals that receive these vaccine booster doses and treatments is unclear. We investigated the association between seropositivity to SARSCoV-2 spike protein with demographic, disease, and treatment- related characteristics after at least three COVID-19 vaccines in three cohorts of people who are immunosuppressed.Methods In a cross-sectional study using UK national disease registries, we identified, contacted, and recruited recipients of solid organ transplants, participants with rare autoimmune rheumatic diseases, and participants with lymphoid malignancies who were 18 years or older, resident in the UK, and who had received at least three doses of a COVID-19 vaccine. The study was open to recruitment from Dec 7, 2021, to June 26, 2022. Participants received a lateral flow immunoassay test for SARS-CoV-2 spike antibodies to complete at home, and an online questionnaire. Multivariable logistic regression was used to estimate the mutually adjusted odds of seropositivity against each characteristic.FindingsBetween Feb 14 and June 26, 2022, we screened 101 972 people (98 725 invited, 3247 self-enrolled) and recruited 28 411 (27·9%) to the study. 23 036 (81·1%) recruited individuals provided serological data. Of these, 9927 (43·1%) were recipients of solid organ transplants, 6516 (28·3%) had rare autoimmune rheumatic diseases, and 6593 (28·6%) had lymphoid malignancies. 10 485 (45·5%) participants were men and 12 535 (54·4%) were women (gender was not reported for 16 [<0·1%] participants), and 21661 (94·0%) participants were of White ethnicity. The median age of participants with solid organ transplants was 60 years (SD 50–67), with rare autoimmune rheumatic diseases was 65 years (54–73), and with lymphoid malignancy was 69 years (61–75). Of the 23 036 participants with serological data, 6583 (28·6%) had received three vaccine doses, 14 234 (61·8%) had received four vaccine doses, and 2219 (9·6%) had received five or more vaccine doses. IgG anti-spike antibodies were undetectable in 2310 (23·3%) of 9927 patients with solid organ transplants, 922 (14·1%) of 6516 patients with rare autoimmune rheumatic diseases, and 1366 (20·7%) of 6593 patients with lymphoid malignancies. In all groups, seropositivity was associated with younger age, higher number of vaccine doses (ie, five vs three), and previous COVID-19. Immunosuppressive medication reduced the likelihood of seropositivity: the lowest odds of seropositivity were found in recipients of solid organ transplants receiving a combination of an anti-proliferative agent, a calcineurin inhibitor, and steroids, and those with rare autoimmune rheumatic diseases or lymphoid malignancies treated with anti-CD20 therapies. InterpretationApproximately one in five recipients of solid organ transplants, individuals with rare autoimmune rheumatic diseases, and individuals with lymphoid malignancies have no detectable IgG anti-spike antibodies despite three or more vaccine doses, but this proportion decreases with sequential booster doses. Choice of immunosuppressant and disease type is strongly associated with serological response. Antibody testing using lateral flow immunoassay tests could enable rapid identification of individuals who are most likely to benefit from additional COVID-19 interventions

Global profiling of protein lipidation using chemical proteomic technologies

Protein lipidation is unique amongst post-translational modifications (PTMs) in enabling direct interaction with cell membranes, and is found in every form of life. Lipidation is important in normal function and in disease, but its intricate interplay with disease context presents a challenging for drug development. Global whole-proteome profiling of protein lipidation lies beyond the range of standard methods, but is well-suited to metabolic tagging with small ‘clickable’ chemical reporters that do not disrupt metabolism and function; chemoselective reactions are then used to add multifunctional labels exclusively to tagged-lipidated proteins. This chemical proteomic technology has opened up the first quantitative whole-proteome studies of the known major classes of protein lipidation, and the first insights into their full scope in vivo

Competition-based, quantitative chemical proteomics in breast cancer cells identifies new target profiles for sulforaphane

Sulforaphane is a small molecule isothiocyanate which exhibits anticancer potential, yet its biological targets remain poorly understood. Here we employ a competition-based chemical proteomics strategy to profile sulforaphane’s targets and identify over 500 targets along with their relative affinities. These targets provide a new set of mediators for sulforaphane’s bioactivity, and aid understanding of its complex mode of action

Discovery of a Potent and Selective Covalent Inhibitor and Activity-Based Probe for the Deubiquitylating Enzyme UCHL1, with Anti-Fibrotic Activity

Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) is a deubiquitylating enzyme which is proposed as a potential therapeutic target in neurodegeneration, cancer, and liver and lung fibrosis. Herein we report the discovery of the most potent and selective UCHL1 probe (IMP-1710) to date based on a covalent inhibitor scaffold and apply this probe to identify and quantify target proteins in intact human cells. IMP-1710 stereoselectively labels the catalytic cysteine of UCHL1 at low nanomolar concentration in cells, and we show that a previously claimed UCHL1 inhibitor (LDN-57444) fails to engage UCHL1 in cells. We further demonstrate that potent UCHL1 inhibitors block pro-fibrotic responses in a cellular model of idiopathic pulmonary fibrosis, supporting a potential therapeutic role for UCHL1 inhibition and providing a basis for future therapeutic development of selective UCHL1 inhibitors