The NIH Somatic Cell Genome Editing program.

The move from reading to writing the human genome offers new opportunities to improve human health. The United States National Institutes of Health (NIH) Somatic Cell Genome Editing (SCGE) Consortium aims to accelerate the development of safer and more-effective methods to edit the genomes of disease-relevant somatic cells in patients, even in tissues that are difficult to reach. Here we discuss the consortium's plans to develop and benchmark approaches to induce and measure genome modifications, and to define downstream functional consequences of genome editing within human cells. Central to this effort is a rigorous and innovative approach that requires validation of the technology through third-party testing in small and large animals. New genome editors, delivery technologies and methods for tracking edited cells in vivo, as well as newly developed animal models and human biological systems, will be assembled-along with validated datasets-into an SCGE Toolkit, which will be disseminated widely to the biomedical research community. We visualize this toolkit-and the knowledge generated by its applications-as a means to accelerate the clinical development of new therapies for a wide range of conditions.

Total Synthesis of a PSGL-1 Glycopeptide Analogue for Targeted Inhibition of P-Selectin.

The high affinity interaction between P-selectin glycoprotein ligand-1 (PSGL-1) and P-selectin is mediated by a multimotif glycosulfopeptide (GSP) recognition domain consisting of clustered tyrosine sulfates and a Core 2 O-glycan terminated with sialyl LewisX (C2-O-sLeX). These distinct GSP motifs are much more common than previously appreciated within a wide variety of functionally important domains involved in protein-protein interactions. However, despite the potential of GSPs to serve as tools for fundamental studies and prospects for drug discovery, their utility has been limited by the absence of chemical schemes for synthesis on scale. Herein, we report the total synthesis of GSnP-6, an analogue of the N-terminal domain of PSGL-1, and potent inhibitor of P-selectin. An efficient, scalable, hydrogenolysis-free synthesis of C2-O-sLeX-Thr-COOH was identified by both convergent and orthogonal one-pot assembly, which afforded this crucial building block, ready for direct use in solid phase peptide synthesis (SPPS). C2-O-sLeX-Thr-COOH was synthesized in 10 steps with an overall yield of 23% from the 4-O,5-N oxazolidinone thiosialoside donor. This synthesis represents an 80-fold improvement in reaction yield as compared to prior reports, achieving the first gram scale synthesis of SPPS ready C2-O-sLeX-Thr-COOH and enabling the scalable synthesis of GSnP-6 for preclinical evaluation. Significantly, we established that GSnP-6 displays dose-dependent inhibition of venous thrombosis in vivo and inhibits vaso-occlusive events in a human sickle cell disease equivalent microvasculature-on-a-chip system. The insights gained in formulating this design strategy can be broadly applied to the synthesis of a wide variety of biologically important oligosaccharides and O-glycan bearing glycopeptides.

Targeting altered glycosylation in secreted tumor glycoproteins for broad cancer detection.

There is an urgent need to develop new tumor biomarkers for early cancer detection, but the variability of tumor-derived antigens has been a limitation. Here we demonstrate a novel anti-Tn antibody microarray platform to detect Tn+ glycoproteins, a near universal antigen in carcinoma-derived glycoproteins, for broad detection of cancer. The platform uses a specific recombinant IgG1 to the Tn antigen (CD175) as a capture reagent and a recombinant IgM to the Tn antigen as a detecting reagent. These reagents were validated by immunohistochemistry in recognizing the Tn antigen using hundreds of human tumor specimens. Using this approach, we could detect Tn+ glycoproteins at subnanogram levels using cell lines and culture media, serum, and stool samples from mice engineered to express the Tn antigen in intestinal epithelial cells. The development of a general cancer detection platform using recombinant antibodies for detection of altered tumor glycoproteins expressing a unique antigen could have a significant impact on cancer detection and monitoring.

A PSGL-1 glycomimetic reduces thrombus burden without affecting hemostasis.

Events mediated by the P-selectin/PSGL-1 pathway play a critical role in the initiation and propagation of venous thrombosis by facilitating the accumulation of leukocytes and platelets within the growing thrombus. Activated platelets and endothelium express P-selectin, which binds P-selectin glycoprotein ligand-1 (PSGL-1) that is expressed on the surface of all leukocytes. We developed a pegylated glycomimetic of the N terminus of PSGL-1, PEG40-GSnP-6 (P-G6), which proved to be a highly potent P-selectin inhibitor with a favorable pharmacokinetic profile for clinical translation. P-G6 inhibits human and mouse platelet-monocyte and platelet-neutrophil aggregation in vitro and blocks microcirculatory platelet-leukocyte interactions in vivo. Administration of P-G6 reduces thrombus formation in a nonocclusive model of deep vein thrombosis with a commensurate reduction in leukocyte accumulation, but without disruption of hemostasis. P-G6 potently inhibits the P-selectin/PSGL-1 pathway and represents a promising drug candidate for the prevention of venous thrombosis without increased bleeding risk.

Anatomic eligibility for endovascular aneurysm repair preserved over 2 years of surveillance.

OBJECTIVE: Endovascular aneurysm repair (EVAR) is a widely used option for patients with suitable vascular anatomy who have a large infrarenal abdominal aortic aneurysm (AAA). Patients with small AAAs are managed with careful surveillance and it is a common concern that their anatomy may change with AAA growth, and their option for EVAR may become limited. Device innovation has resulted in expanded ranges of anatomy that may be eligible for EVAR. This study sought to identify changes in anatomic eligibility for repair with contemporary endovascular devices in AAA patients, monitored by computed tomography scan over the course of 2 years. METHODS: Patients from the Non-Invasive Treatment of Abdominal Aortic Aneurysm Clinical Trial (N-TA3CT, NCT01756833) were included in this analysis. Females had baseline AAA maximum transverse diameter between 3.5 and 4.5 cm, and males had baseline maximum transverse diameter between 3.5 and 5.0 cm. Patients were included in this analysis if they completed pre-enrollment and 2-year follow-up computed tomography imaging. Pertinent anatomic measurements were performed on a postprocessing workstation in a centralized imaging core laboratory. EVAR candidacy was determined by measuring proximal aortic neck diameter, AAA length, and infrarenal neck angulation. Patients were considered to be eligible for EVAR if they qualified for at least one of the seven studied devices' instructions for use at baseline and at 2 years. A paired t test analysis was used to detect differences in aortic measurements over 2 years, and the McNemar test was used to compare eligibility over 2 years. RESULTS: We included 192 patients in this analysis-168 male and 24 female. Of these patients, 85% were eligible for EVAR at baseline and 85% after 2 years of follow-up (P = 1.00; 95% confidence interval -0.034 to 0.034). Of the 164 EVAR candidates at baseline, 160 (98%) remained eligible over 2 years of surveillance. Insufficient neck length was the most common reason for both ineligibility at baseline (18 of 28 patients) as well as loss of candidacy over 2 years (3 of 4 patients). CONCLUSIONS: The majority of patients eligible for EVAR when entering a surveillance program for small AAA remain eligible after 2 years. Substantial changes in AAA neck anatomy resulting in loss of EVAR treatment options are infrequent. Patients with anatomic AAA progression beyond EVAR eligibility remain candidates for complex EVAR and open repair.

Standardized User-Independent Confocal Microscopy Image Acquisition and Analysis for Thickness Measurements of Microscale Collagen Scaffolds.

The ability to accurately and precisely measure the thickness of biomaterial constructs is critical for characterizing both specific dimensional features and related mechanical properties. However, in the absence of a standardized approach for thickness measurements, a variety of imaging modalities have been employed, which have been associated with varying limits of accuracy, particularly for ultrathin hydrated structures. Electron microscopy (EM), a commonly used modality, yields thickness values for extensively processed and nonhydrated constructs, potentially resulting in overestimated mechanical properties, including elastic modulus and ultimate tensile strength. Confocal laser scanning microscopy (CLSM) has often been used as a nondestructive imaging alternative. However, published CLSM-derived image analysis protocols use arbitrary signal intensity cutoffs and provide minimal information regarding thickness variability across imaged surfaces. To address the aforementioned limitations, we present a standardized, user-independent CLSM image acquisition and analysis approach developed as a custom ImageJ macro and validated with collagen-based scaffolds. In the process, we also quantify thickness discrepancies in collagen-based scaffolds between CLSM and EM techniques, further illustrating the need for improved strategies. Employing the same image acquisition protocol, we also demonstrate that this approach can be used to estimate the surface roughness of the same scaffolds without the use of specialized instrumentation.

Identification of Tn antigen O-GalNAc-expressing glycoproteins in human carcinomas using novel anti-Tn recombinant antibodies.

The Tn antigen is a neoantigen abnormally expressed in many human carcinomas and expression correlates with metastasis and poor survival. To explore its biomarker potential, new antibodies are needed that specifically recognize this antigen in tumors. Here we generated two recombinant antibodies to the Tn antigen, Remab6 as a chimeric human IgG1 antibody and ReBaGs6 as a murine IgM antibody and characterized their specificities using multiple biochemical and biological approaches. Both Remab6 and ReBaGs6 recognize clustered Tn structures, but most importantly do not recognize glycoforms of human IgA1 that contain potential cross-reactive Tn antigen structures. In flow cytometry and immunofluorescence analyses, Remab6 recognizes human cancer cell lines expressing the Tn antigen, but not their Tn-negative counterparts. In immunohistochemistry (IHC), Remab6 stains many human cancers in tissue array format but rarely stains normal tissues and then mostly intracellularly. We used these antibodies to identify several unique Tn-containing glycoproteins in Tn-positive Colo205 cells, indicating their utility for glycoproteomics in future biomarker studies. Thus, recombinant Remab6 and ReBaGs6 are useful for biochemical characterization of cancer cells and IHC of tumors and represent promising tools for Tn biomarker discovery independently of recognition of IgA1.

Vascular Quality Initiative assessment of compliance with Society for Vascular Surgery clinical practice guidelines on the care of patients with abdominal aortic aneurysm.

OBJECTIVE: Professional societies publish clinical practice guidelines to provide evidence-based recommendations to improve care and to reduce practice variation. However, the degree of compliance with the guidelines and its impact on outcomes have not been well defined. This study used the Vascular Quality Initiative (VQI) abdominal aortic aneurysm (AAA) registries to determine current compliance with and impact of recent Society for Vascular Surgery (SVS) AAA guidelines. METHODS: Recommendations from the SVS AAA guidelines were reviewed and assessed as to whether they could be evaluated with current VQI data sets. The degree of compliance with these individual recommendations was calculated by center and correlated with clinical outcomes. Data were analyzed by univariate analysis and mixed effects multivariable logistic regression. Statistical significance was measured at P < .05. RESULTS: Of the 111 SVS recommendations, 10 could be evaluated using VQI registries. The mean center-specific compliance rate ranged from 40% (smoking cessation 2 weeks before open AAA [OAAA] repair) to 99% (preservation of flow to one internal iliac artery during endovascular aneurysm repair [EVAR]). Some recommendations were associated with improved outcomes (eg, cell salvage for OAAA repair and antibiotic prophylaxis), whereas others were not (eg, EVAR at a center with >10 cases per year or door-to-intervention time <90 minutes for ruptured AAA). With multivariable analysis, compliance with preservation of flow to the internal iliac artery decreased major adverse cardiac events in EVAR and marginally decreased in-hospital and 1-year mortality in OAAA repair. Antibiotic administration decreased surgical site infection, major adverse cardiac events, and in-hospital mortality and marginally decreased respiratory complications and 1-year mortality in EVAR. Cell salvage for OAAA repair decreased 1-year mortality. Tobacco cessation before EVAR or OAAA repair decreased respiratory complications and 1-year mortality. CONCLUSIONS: The VQI registry is a valuable tool that can be used to measure compliance with SVS AAA guidelines. Compliance with recommendations was associated with improved outcomes and should be encouraged for providers. Participation in the VQI registry provides an objective assessment of performance and compliance with guidelines. VQI provider and center reports may be used as a focus for quality improvement efforts.

Multisource Evaluation of Surgeon Behavior Is Associated With Malpractice Claims.

OBJECTIVE: We merged direct, multisource, and systematic assessments of surgeon behavior with malpractice claims, to analyze the relationship between surgeon 360-degree reviews and malpractice history. BACKGROUND: Previous work suggests that malpractice claims are associated with a poor physician-patient relationship, which is likely related to behaviors captured by 360-degree review. We hypothesize that 360-degree review results are associated with malpractice claims. METHODS: Surgeons from 4 academic medical centers covered by a common malpractice carrier underwent 360-degree review in 2012 to 2013 (n = 385). Matched, de-identified reviews and malpractice claims data were available for 264 surgeons from 2000 to 2015. We analyzed 23 questions, highlighting positive and negative behaviors within the domains of education, excellence, humility, openness, respect, service, and teamwork. Regression analysis with robust standard error was used to assess the potential association between 360-degree review results and malpractice claims. RESULTS: The range of claims among the 264 surgeons was 0 to 8, with 48.1% of surgeons having at least 1 claim. Multiple positive and negative behaviors were significantly associated with the risk of having malpractice claims (P < 0.05). Surgeons in the bottom decile for several items had an increased likelihood of having at least 1 claim. CONCLUSION: Surgeon behavior, as assessed by 360-degree review, is associated with malpractice claims. These findings highlight the importance of teamwork and communication in exposure to malpractice. Although the nature of malpractice claims is complex and multifactorial, the identification and modification of negative physician behaviors may mitigate malpractice risk and ultimately result in the improved quality of patient care.

Selectin catch-bonds mechanotransduce integrin activation and neutrophil arrest on inflamed endothelium under shear flow.

E-selectin extends from the plasma membrane of inflamed endothelium and serves to capture leukocytes from flowing blood via long-lived catch-bonds that support slow leukocyte rolling under shear stress. Its ligands are glycosylated with the tetrasaccharide sialyl Lewisx (sLex), which contributes to bond affinity and specificity. E-selectin-mediated rolling transmits signals into neutrophils that trigger activation of high-affinity ß2-integrins necessary for transition to shear-resistant adhesion and transendothelial migration. Rivipansel is a glycomimetic drug that inhibits E-selectin-mediated vaso-occlusion induced by integrin-dependent sickle-red blood cell-leukocyte adhesion. How Rivipansel antagonizes ligand recognition by E-selectin and blocks outside-in signaling of integrin-mediated neutrophil arrest while maintaining rolling immune-surveillance is unknown. Here, we demonstrate that sLex expressed on human L-selectin is preferentially bound by E-selectin and, on ligation, initiates secretion of MRP8/14 that binds TLR4 to elicit the extension of ß2-integrin to an intermediate affinity state. Neutrophil rolling over E-selectin at precise shear stress transmits tension and catch-bond formation with L-selectin via sLex, resulting in focal clusters that deliver a distinct signal to upshift ß2-integrins to a high-affinity state. Rivipansel effectively blocked formation of selectin catch-bonds, revealing a novel mechanotransduction circuit that rapidly converts extended ß2-integrins to high-affinity shear-resistant bond clusters with intracellular adhesion molecule 1 on inflamed endothelium.

Design and Implementation of an Infrastructure Program to Support Clinical Research in Surgery.

Barriers to active participation in clinical research among academic surgeons include insufficient research training and mentorship, increased clinical demands, lack of protected research time, limited access to resources, complex regulatory requirements, and a highly competitive research funding environment. We describe the development and implementation of a novel clinical research infrastructure program designed to attenuate these barriers and increase clinical research engagement and productivity in a large academic surgery department. Interim outcomes show a high utilization of program services across all divisions within the department, a substantial increase in new clinical research protocols, more applications submitted to funding agencies, and a high level of user satisfaction. We discuss how a departmental infrastructure program can simultaneously address barriers faced by surgeon clinical researchers and foster continuation of the longstanding tradition of innovation and discovery in academic surgery.

Isotopic labeling with cellular O-glycome reporter/amplification (ICORA) for comparative O-glycomics of cultured cells.

Mucin-type O-glycans decorate >80% of secretory and cell surface proteins and contribute to health and disease. However, dynamic alterations in the O-glycome are poorly understood because current O-glycomic methodologies are not sufficiently sensitive nor quantitative. Here we describe a novel isotope labeling approach termed Isotope-Cellular O-glycome Reporter Amplification (ICORA) to amplify and analyze the O-glycome from cells. In this approach, cells are incubated with Ac3GalNAc-Bn (Ac3GalNAc-[1H7]Bn) or a heavy labeled Ac3GalNAc-BnD7 (Ac3GalNAc-[2D7]Bn) O-glycan precursor (7 Da mass difference), which enters cells and upon de-esterification is modified by Golgi enzymes to generate Bn-O-glycans secreted into the culture media. After recovery, heavy and light Bn-O-glycans from two separate conditions are mixed, analyzed by MS, and statistically interrogated for changes in O-glycan abundance using a semi-automated approach. ICORA enables ~100-1000-fold enhanced sensitivity and increased throughput compared to traditional O-glycomics. We validated ICORA with model cell lines and used it to define alterations in the O-glycome in colorectal cancer. ICORA is a useful tool to explore the dynamic regulation of the O-glycome in health and disease.

A systematic review of surveillance after endovascular aortic repair.

OBJECTIVE: The objective of this systematic review and meta-analysis was to evaluate the optimal modality and frequency of surveillance after endovascular aortic repair (EVAR) in adult patients with abdominal aortic aneurysms. METHODS: We searched for studies of post-EVAR surveillance in MEDLINE In-Process & Other Non-Indexed Citations, MEDLINE, Embase, Cochrane Database of Systematic Reviews, and Scopus through May 10, 2016. The outcomes of interest were endoleaks, mortality, limb ischemia, renal complications, late rupture, and aneurysm-related mortality. Outcomes were pooled using a random-effects model and were reported as incidence rate and 95% confidence interval. RESULTS: Of 1099 candidate references, we included 6 meta-analyses and 52 observational studies. Complication rates were common after EVAR, particularly in the first year. Magnetic resonance imaging had a higher detection rate of endoleaks than computed tomography angiography. Doppler ultrasound had lower diagnostic accuracy, whereas contrast-enhanced ultrasound was likely to be as sensitive as computed tomography angiography. The highest endoleak detection rates were in surveillance approaches that used combined tests. There were no studies that compared different surveillance intervals to determine optimal intervals; however, most studies reported detection rates of patient-important outcomes at 1, 6, 12, 24, 36, 48, and 60 months. Data were insufficient to provide comparative inferences about the best strategy to reduce the risk of patient-important outcomes, such as mortality, limb ischemia, rupture, and renal complications. CONCLUSIONS: Several tests with reasonable diagnostic accuracy are available for surveillance after EVAR. The available evidence suggests a high complication rate, particularly in the first year, and provides a rationale for surveillance.

Vascular fellow and resident experience performing infrapopliteal revascularization with endovascular procedures and vein bypass during training.

OBJECTIVE: Endovascular aneurysm repair has led to a significant reduction in vascular trainee experience in the surgical treatment of aortic aneurysms. We sought to evaluate whether the vascular training paradigm or the "endovascular first" approach to lower extremity vascular disease has had a similar effect on trainee experience with infrapopliteal endovascular therapy and vein bypass. METHODS: Deidentified data were provided by the Vascular Surgery Board on the number of procedures performed by each 2014 fellowship and residency (0 + 5) graduate during training. Data were analyzed using parametric and nonparametric methods, where appropriate. RESULTS: Of 125 trainees (109 fellows, 16 residents), 33 (27%) performed 10 or fewer infrapopliteal vein bypasses and 37 (29%) performed 10 or fewer infrapopliteal endovascular procedures during their training. Eleven trainees (9%) performed 10 or fewer of both procedures. There was a positive correlation between number of infrapopliteal vein bypass and endovascular procedures performed (r = 0.19; P = .03). There was no difference between fellows and residents in the mean number of bypass operations performed during training (17.3 vs 19.1; P = .50; range, 0-53). However, residents performed more infrapopliteal endovascular procedures than fellows did (median, 29 vs 16; P = .03; range, 0-128). CONCLUSIONS: More than one in four graduates of both training paradigms finish with a low number of infrapopliteal bypasses and endovascular interventions. The number of these procedures needed for proficiency is not known. Vascular surgery training programs should critically evaluate the number of infrapopliteal procedures required to achieve proficiency.

The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm.

BACKGROUND: Decision-making related to the care of patients with an abdominal aortic aneurysm (AAA) is complex. Aneurysms present with varying risks of rupture, and patient-specific factors influence anticipated life expectancy, operative risk, and need to intervene. Careful attention to the choice of operative strategy along with optimal treatment of medical comorbidities is critical to achieving excellent outcomes. Moreover, appropriate postoperative surveillance is necessary to minimize subsequent aneurysm-related death or morbidity. METHODS: The committee made specific practice recommendations using the Grading of Recommendations Assessment, Development, and Evaluation system. Three systematic reviews were conducted to support this guideline. Two focused on evaluating the best modalities and optimal frequency for surveillance after endovascular aneurysm repair (EVAR). A third focused on identifying the best available evidence on the diagnosis and management of AAA. Specific areas of focus included (1) general approach to the patient, (2) treatment of the patient with an AAA, (3) anesthetic considerations and perioperative management, (4) postoperative and long-term management, and (5) cost and economic considerations. RESULTS: Along with providing guidance regarding the management of patients throughout the continuum of care, we have revised a number of prior recommendations and addressed a number of new areas of significance. New guidelines are provided for the surveillance of patients with an AAA, including recommended surveillance imaging at 12-month intervals for patients with an AAA of 4.0 to 4.9 cm in diameter. We recommend endovascular repair as the preferred method of treatment for ruptured aneurysms. Incorporating knowledge gained through the Vascular Quality Initiative and other regional quality collaboratives, we suggest that the Vascular Quality Initiative mortality risk score be used for mutual decision-making with patients considering aneurysm repair. We also suggest that elective EVAR be limited to hospitals with a documented mortality and conversion rate to open surgical repair of 2% or less and that perform at least 10 EVAR cases each year. We also suggest that elective open aneurysm repair be limited to hospitals with a documented mortality of 5% or less and that perform at least 10 open aortic operations of any type each year. To encourage the development of effective systems of care that would lead to improved outcomes for those patients undergoing emergent repair, we suggest a door-to-intervention time of <90 minutes, based on a framework of 30-30-30 minutes, for the management of the patient with a ruptured aneurysm. We recommend treatment of type I and III endoleaks as well as of type II endoleaks with aneurysm expansion but recommend continued surveillance of type II endoleaks not associated with aneurysm expansion. Whereas antibiotic prophylaxis is recommended for patients with an aortic prosthesis before any dental procedure involving the manipulation of the gingival or periapical region of teeth or perforation of the oral mucosa, antibiotic prophylaxis is not recommended before respiratory tract procedures, gastrointestinal or genitourinary procedures, and dermatologic or musculoskeletal procedures unless the potential for infection exists or the patient is immunocompromised. Increased utilization of color duplex ultrasound is suggested for postoperative surveillance after EVAR in the absence of endoleak or aneurysm expansion. CONCLUSIONS: Important new recommendations are provided for the care of patients with an AAA, including suggestions to improve mutual decision-making between the treating physician and the patients and their families as well as a number of new strategies to enhance perioperative outcomes for patients undergoing elective and emergent repair. Areas of uncertainty are highlighted that would benefit from further investigation in addition to existing limitations in diagnostic tests, pharmacologic agents, intraoperative tools, and devices.

Convergent Synthesis of Sialyl LewisX- O-Core-1 Threonine.

Selectins are a class of cell adhesion molecules that play a critical role during the initial steps of inflammation. The N-terminal domain of P-selectin glycoprotein ligand-1 (PSGL-1) binds to all selectins, but with the highest affinity to P-selectin. Recent evidence suggests that the blockade of P-selectin/PSGL-1 interactions provides a viable therapeutic option for the treatment of many inflammatory diseases. Herein, we report the total synthesis of threonine bearing sialyl LewisX (sLeX) linked to a Core-1- O-hexasaccharide 1, as a key glycan of the N-terminal domain of PSGL-1. A convergent synthesis using α-selective sialylation and a regioselective [4+2] glycosylation are the key features of this synthesis.

Efferocytosis as a regulator of macrophage chemokine receptor expression and polarization.

Efferocytosis has been suggested to promote macrophage resolution programs that are dependent on motility and emigration, however, few studies have addressed directed migration in resolving macrophages. In this report, we hypothesized that efferocytosis would induce differential chemokine receptor expression. Polarized macrophage populations, including macrophages actively engaged in efferocytosis, were characterized by PCR array and traditional transwell motility assays. We identified specific up-regulation of chemokine receptor CXCR4 on both mouse and human macrophages and characterized in vivo expression of CXCR4 in a resolving model of murine peritonitis. Using adoptive transfer and AMD3100 blocking, we confirmed a role for CXCR4 in macrophage egress to draining lymphatics. Collectively these data provide an important mechanistic link between efferocytosis and macrophage emigration.

Reprogramming the specificity of sortase enzymes.

Staphylococcus aureus sortase A catalyzes the transpeptidation of an LPXTG peptide acceptor and a glycine-linked peptide donor and has proven to be a powerful tool for site-specific protein modification. The substrate specificity of sortase A is stringent, limiting its broader utility. Here we report the laboratory evolution of two orthogonal sortase A variants that recognize each of two altered substrates, LAXTG and LPXSG, with high activity and specificity. Following nine rounds of yeast display screening integrated with negative selection, the evolved sortases exhibit specificity changes of up to 51,000-fold, relative to the starting sortase without substantial loss of catalytic activity, and with up to 24-fold specificity for their target substrates, relative to their next most active peptide substrate. The specificities of these altered sortases are sufficiently orthogonal to enable the simultaneous conjugation of multiple peptide substrates to their respective targets in a single solution. We demonstrated the utility of these evolved sortases by using them to effect the site-specific modification of endogenous fetuin A in human plasma, the synthesis of tandem fluorophore-protein-PEG conjugates for two therapeutically relevant fibroblast growth factor proteins (FGF1 and FGF2), and the orthogonal conjugation of fluorescent peptides onto surfaces.