Peri-operative SARS-CoV-2 infection increases postoperative mortality. The aim of this study was to determine the optimal duration of planned delay before surgery in patients who have had SARS-CoV-2 infection. This international, multicentre, prospective cohort study included patients undergoing elective or emergency surgery during October 2020. Surgical patients with pre-operative SARS-CoV-2 infection were compared with those without previous SARS-CoV-2 infection. The primary outcome measure was 30-day postoperative mortality. Logistic regression models were used to calculate adjusted 30-day mortality rates stratified by time from diagnosis of SARS-CoV-2 infection to surgery. Among 140,231 patients (116 countries), 3127 patients (2.2%) had a pre-operative SARS-CoV-2 diagnosis. Adjusted 30-day mortality in patients without SARS-CoV-2 infection was 1.5% (95%CI 1.4-1.5). In patients with a pre-operative SARS-CoV-2 diagnosis, mortality was increased in patients having surgery within 0-2 weeks, 3-4 weeks and 5-6 weeks of the diagnosis (odds ratio (95%CI) 4.1 (3.3-4.8), 3.9 (2.6-5.1) and 3.6 (2.0-5.2), respectively). Surgery performed ≥ 7 weeks after SARS-CoV-2 diagnosis was associated with a similar mortality risk to baseline (odds ratio (95%CI) 1.5 (0.9-2.1)). After a ≥ 7 week delay in undertaking surgery following SARS-CoV-2 infection, patients with ongoing symptoms had a higher mortality than patients whose symptoms had resolved or who had been asymptomatic (6.0% (95%CI 3.2-8.7) vs. 2.4% (95%CI 1.4-3.4) vs. 1.3% (95%CI 0.6-2.0), respectively). Where possible, surgery should be delayed for at least 7 weeks following SARS-CoV-2 infection. Patients with ongoing symptoms ≥ 7 weeks from diagnosis may benefit from further delay.

Chemical cross-linking is an attractive approach to map peptide-protein and protein-protein complexes. Previously, we explored 3,4-dihydroxylphenylalanine (DOPA) as a protein cross-linking agent upon periodate oxidation.(Burdine, L.; Gillette, T. G.; Lin, H-J.; Kodadek, T. J. Am. Chem. Soc. 2004, 126, 11442-11443) We report here a study on the chemistry of DOPA-protein crosslinking. First, using a peptide nucleic acid (PNA) templated system, we identified the α-amino, ε-amino of Lys, imidazole of His, and thiol of Cys as functional groups capable of attacking DOPA ortho-quinone. Second, we demonstrated that periodate-induced DOPA-protein cross-linking could be carried out efficiently at neutral pH in the presence of excess aliphatic 1,2-diols such as ethylene glycol, lactose, and ATP. This result indicated that DOPA-protein cross-linking and 1,2-diol oxidative cleavage proceed via different mechanisms and, that carbohydrates will not interfere with this process when carried out in crude cell extracts or on intact cells.Protein-protein interactions are of fundamental importance in almost all biological processes. In some cases, these are strong, stable contacts while in others they represent much weaker, transient interactions. In principle, chemical cross-linking followed by detailed product analysis is an attractive approach to map protein-protein contacts under native conditions. However, this is complicated by the low reactivity of typical bifunctional cross-linking reagents and their tendency to produce false positives (reviewed in references 1, 2 ). As part of a program to develop a new generation of more efficient and useful cross-linking reagents, we have shown recently that molecules containing 3,4-dihydroxylphenylalanine (DOPA) often cross-link efficiently to their protein receptors when treated with sodium periodate. 3 Under these conditions, DOPA is converted to an ortho-quinone intermediate that can be attacked by nearby nucleophiles, resulting in a stable cross-link. 4 Using as a model system a high affinity complex comprised of the yeast Gal80 protein and a DOPA-containing peptide mimicking the Gal4 activation domain, 5-7 we showed that this chemistry provided a high yield of cross-linked product when the purified components were mixed together in standard biochemical buffers or in crude cell extracts. The reaction was relatively rapid, reaching completion in less than one minute. Finally, control experiments demonstrated that no coupling occurred unless the DOPA-containing molecule was specifically bound to the protein receptor, suggesting that false positives will be rare using this chemistry.As DOPA appears to be a promising cross-linking agent with which to study peptide-protein and protein-protein interactions, it is important to understand the mechanism of cross-linking in more detail. While it seems clear that the critical intermediate is an ortho-quinone, it is less *Corresponding author. Thomas.Kodadek@utsouthwestern.edu. In this study, we report the results of experiments design...

out such experiments, particularly biochemical assays, which are underappreciated but can have a significant impact on the success or failure of a protein "fishing expedition." It is our hope that some of the points raised here will stimulate and aid new research into this impor-

Chemical cross-linking is a powerful methodology for analyzing proteins-small molecule and protein-protein interactions. We describe the development of a new chemical cross-linking reaction for the study of protein complexes. Specifically, we show that molecules containing an ortho dihydroxyarene unit can be oxidized selectively with sodium periodate in the presence of native proteins, producing an ortho quinone intermediate that can cross-link with suitable nearby protein residues. We demonstrate the efficacy and specificity of this chemistry for a peptide-protein complex and also deduce the binding site of an artificial activation domain on a proteasome subcomplex.

SARS-CoV-2 has been associated with an increased rate of venous thromboembolism in critically ill patients. Since surgical patients are already at higher risk of venous thromboembolism than general populations, this study aimed to determine if patients with peri-operative or prior SARS-CoV-2 were at further increased risk of venous thromboembolism. We conducted a planned sub-study and analysis from an international, multicentre, prospective cohort study of elective and emergency patients undergoing surgery during October 2020. Patients from all surgical specialties were included. The primary outcome measure was venous thromboembolism (pulmonary embolism or deep vein thrombosis) within 30 days of surgery. SARS-CoV-2 diagnosis was defined as peri-operative (7 days before to 30 days after surgery); recent (1-6 weeks before surgery); previous (≥7 weeks before surgery); or none. Information on prophylaxis regimens or pre-operative anti-coagulation for baseline comorbidities was not available. Postoperative venous thromboembolism rate was 0.5% (666/123,591) in patients without SARS-CoV-2; 2.2% (50/2317) in patients with peri-operative SARS-CoV-2; 1.6% (15/953) in patients with recent SARS-CoV-2; and 1.0% (11/1148) in patients with previous SARS-CoV-2. After adjustment for confounding factors, patients with peri-operative (adjusted odds ratio 1.5 (95%CI 1.1-2.0)) and recent SARS-CoV-2 (1.9 (95%CI 1.2-3.3)) remained at higher risk of venous thromboembolism, with a borderline finding in previous SARS-CoV-2 (1.7 (95%CI 0.9-3.0)). Overall, venous thromboembolism was independently associated with 30-day mortality ). In patients with SARS-CoV-2, mortality without venous thromboembolism was 7.4% (319/4342) and with venous thromboembolism was 40.8% (31/76). Patients undergoing surgery with peri-operative or recent SARS-CoV-2 appear to be at increased risk of postoperative venous thromboembolism compared with patients with no history of SARS-CoV-2 infection. Optimal venous thromboembolism prophylaxis and treatment are unknown in this cohort of patients, and these data should be interpreted accordingly.

Destabilization of activator-DNA complexes by the proteasomal ATPases can inhibit transcription by limiting activator interaction with DNA. Modification of the activator by monoubiquitylation protects the activator from this destabilization activity. In this study, we probe the mechanism of this protective effect of monoubiquitylation. Using novel label transfer and chemical cross-linking techniques, we show that ubiquitin contacts the ATPase complex directly, apparently via Rpn1 and Rpt1. This interaction results in the dissociation of the activation domain-ATPase complex via an allosteric process. A model is proposed in which activator monoubiquitylation serves to limit the lifetime of the activator-ATPase complex interaction and thus the ability of the ATPases to unfold the activator and dissociate the protein-DNA complex.

The VCA domain of the neuronal Wiskott-Aldrich syndrome protein (N-WASP) is a potent activator of the Arp2/3 complex, a 240 kDa heteroheptameric actin-nucleating assembly. We used site-directed spin labeling of N-WASP peptides in conjunction with methyl-TROSY spectra of the intact, selectively labeled Arp2/3 complex to identify regions of the VCA that are proximal to the ARPC3 subunit of the assembly. We also cross-linked CA peptides to the Arp3, Arp2, ARPC1, and ARPC3 subunits. The combined data suggest that the extreme C-terminus of the A region and the C-terminus of the C region of N-WASP are proximal to ARPC3. These results have implications for the mechanism of Arp2/3 complex activation by VCA peptides. This study also demonstrates the utility of NMR spectroscopy for studying ligand binding events in large, asymmetric, macromolecular assemblies.

A new label transfer method is presented that overcomes most of the limitations of current systems. A protein of interest is tagged with tetra-cysteine sequence (FlAsH Receptor Peptide (FRP)) that binds tightly and specifically to a chimeric molecule 3,4-dihydroxyphenylalanine-biotin-4′,5′-bis (1,3,2-dithioarsolan-2-yl)fluorescein (DOPA-biotin-FlAsH). Upon brief periodate oxidation, the DOPA moiety is cross-linked to nearby surface-exposed nucleophiles. Boiling the products in excess dithiol dissolves the FlAsH-FRP interaction, resulting in transfer of the biotin tag to the partner proteins, allowing them to be identified by standard methods. Most methods to characterize protein-protein interactions require the protein of interest to be displayed as an artificial fusion outside of its native environment. To overcome such limitations, a biochemical method called label transfer has been developed, in which a latent cross-linking agent and some easily detectable tag such as a biotin or a radiolabel are connected to the protein of interest via a cleavable linker. Once the modified protein is incorporated into its native complex, the cross-linking moiety is activated and the linker arm is then cleaved, resulting in transfer of the tag to the partner protein 1. While this approach has been employed in the study of some protein complexes, 2,3 the utility of current label transfer technology is severely limited by the requirement to modify the protein of interest covalently and then reconstitute the complex of interest with the modified protein. The inefficient cross-linking chemistry commonly used in such systems (usually photolysis of aryl azides) also complicates the characterization of partner proteins 3. We report here a new type of label transfer system that eliminates the need for covalent modification of the protein of interest (see Scheme 1). It involves tagging the "bait" protein with a tetracysteine-containing peptide (CCPGCC, here called FRP for FlAsH Receptor