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SummaryPersistent systemic inflammation in persons with HIV (PWH) is accompanied by an increased risk of metabolic disease. Yet, changes in the innate and adaptive immune system in PWH who develop metabolic disease remain poorly defined. Using unbiased approaches, we show that PWH with prediabetes/diabetes have a significantly higher proportion of circulating CD14+monocytes complexed to T cells. The complexed CD3+T cells and CD14+monocytes demonstrate functional immune synapses, increased expression of proinflammatory cytokines, and greater glucose utilization. Furthermore, these complexes harbor more latent HIV DNA compared to CD14+monocytes or CD4+T cells. Our results demonstrate that circulating CD3+CD14+T cell-monocyte pairs represent functional dynamic cellular interactions that likely contribute to inflammation and, in light of their increased proportion, may have a role in metabolic disease pathogenesis. These findings provide an incentive for future studies to investigate T cell-monocyte immune complexes as mechanistic in HIV cure and diseases of aging.Graphical AbstractHighlightsPersons with HIV and diabetes have increased circulating CD3+CD14+T cell-monocyte complexes.CD3+CD14+T cell-monocytes are a heterogenous group of functional and dynamic complexes.We can detect HIV in T cell-monocyte complexes.The proportion of CD3+CD14+T cell-monocyte complexes is positively associated with blood glucose levels and negatively with plasma IL-10 and CD4+T regulatory cells.

Interstitial lung disease (ILD) represents a significant cause of morbidity and mortality in systemic sclerosis (SSc). The purpose of this study was to examine recirculating lymphocytes from SSc patients for potential biomarkers of interstitial lung disease (ILD). Peripheral blood mononuclear cells (PBMCs) were isolated from patients with SSc and healthy controls enrolled in the Vanderbilt University Myositis and Scleroderma Treatment Initiative Center cohort between 9/2017–6/2019. Clinical phenotyping was performed by chart abstraction. Immunophenotyping was performed using both mass cytometry and fluorescence cytometry combined with t-distributed stochastic neighbor embedding analysis and traditional biaxial gating. This study included 34 patients with SSc-ILD, 14 patients without SSc-ILD, and 25 healthy controls. CD21lo/neg cells are significantly increased in SSc-ILD but not in SSc without ILD (15.4 ± 13.3% vs. 5.8 ± 0.9%, p = 0.002) or healthy controls (5.0 ± 0.5%, p lo/neg B cells can be identified from a single biaxial gate, tSNE analysis reveals that the biaxial gate is comprised of multiple distinct subsets, all of which are increased in SSc-ILD. CD21lo/neg cells in both healthy controls and SSc-ILD are predominantly tBET positive and do not have intracellular CD21. Immunohistochemistry staining demonstrated that CD21lo/neg B cells diffusely infiltrate the lung parenchyma of an SSc-ILD patient. Additional work is needed to validate this biomarker in larger cohorts and longitudinal studies and to understand the role of these cells in SSc-ILD.

Background Anti-Jo-1 autoantibodies which recognize histidyl-tRNA synthetase identify patients with the rare rheumatologic disease, anti-histidyl-tRNA synthetase syndrome (Jo-1 ARS), a phenotypically distinct subset of idiopathic inflammatory myopathies (IIM). Jo-1-binding B cells (JBCs) are implicated in disease pathogenesis, yet they have not been studied directly. We therefore aimed to characterize JBCs to better understand how they expand and function in Jo-1 ARS. Methods We enrolled 10 IIM patients diagnosed with Jo-1 ARS, 4 patients with non-Jo-1 IIM, and 8 age- and sex-matched healthy controls. We phenotypically characterized peripheral blood mononuclear cells (PBMCs) ex vivo using flow cytometry to define the B cell subsets in which JBCs reside. We further tested their ability to differentiate into antibody-secreting cells following stimulation in vitro. Results The majority of JBCs were IgM+ (not class-switched). Compared to non-JBCs in the same donors, JBCs contained a higher percentage of autoimmune-prone CD21lo cells and were increased in the CD21lo IgM+ IgD− CD27+ memory subset relative to healthy donor B cells. Whereas non-JBCs were present in the anergic BND B cell subset, JBCs were nearly absent from this compartment. JBCs were detected among plasmablasts in some donors, but a reduced frequency of JBCs differentiated into CD38hi24− plasmablasts compared to non-JBCs present in the same wells following in vitro stimulation. Conclusions JBCs are enriched for autoimmune-prone CD21lo B cells, some of which exhibit a memory phenotype in the peripheral repertoire of Jo-1 ARS patients. JBCs undergo limited class switch and show reduced capacity to differentiate into antibody-secreting cells. This suggests complex B cell biology exists beyond class-switched cells that differentiate to secrete anti-Jo-1 autoantibody (i.e., what is captured through serum autoantibody studies). New Jo-1 ARS therapies should thus ideally target non-class-switched JBCs in addition to those that have undergone IgG class-switching to most effectively block cross-talk with autoreactive T cells.

Supplemental Digital Content is available in the text., IMPORTANCE: Even with its proclivity for older age, coronavirus disease 2019 has been shown to affect all age groups. However, there remains a lack of research focused primarily on the young adult population. OBJECTIVES: To describe the epidemiology and outcomes of coronavirus disease 2019 and identify the risk factors associated with critical illness and mortality in hospitalized young adults. DESIGN, SETTINGS, AND PARTICIPANTS: A retrospective cohort study of the Society of Critical Care Medicine’s Viral Infection and Respiratory Illness Universal Study registry. Patients 18–40 years old, hospitalized from coronavirus disease 2019 from March 2020 to April 2021, were included in the analysis. MAIN OUTCOMES AND MEASURES: Critical illness was defined as a composite of mortality and 21 predefined interventions and complications. Multivariable logistic regression was used to assess associations with critical illness and mortality. RESULTS: Data from 4,005 patients (152 centers, 19 countries, 18.6% non-U.S. patients) were analyzed. The median age was 32 years (interquartile range, 27–37 yr); 51% were female, 29.4% Hispanic, and 42.9% had obesity. Most patients (63.2%) had comorbidities, the most common being hypertension (14.5%) and diabetes (13.7%). Hospital and ICU mortality were 3.2% (129/4,005) and 8.3% (109/1,313), respectively. Critical illness occurred in 25% (n = 996), and 34.3% (n = 1,376) were admitted to the ICU. Older age (p = 0.03), male sex (adjusted odds ratio, 1.83 [95% CI, 1.2–2.6]), and obesity (adjusted odds ratio, 1.6 [95% CI, 1.1–2.4]) were associated with hospital mortality. In addition to the above factors, the presence of any comorbidity was associated with critical illness from coronavirus disease 2019. Multiple sensitivity analyses, including analysis with U.S. patients only and patients admitted to high-volume sites, showed similar risk factors. CONCLUSIONS: Among hospitalized young adults, obese males with comorbidities are at higher risk of developing critical illness or dying from coronavirus disease 2019.

SUMMARYRNA-based vaccines against SARS-CoV-2 are critical to limiting COVID-19 severity and spread. Cellular mechanisms driving antigen-specific responses to these vaccines, however, remain uncertain. We used single-cell technologies to identify and characterized antigen-specific cells and antibody responses to the RNA vaccine BNT162b2 in longitudinal samples from a cohort of healthy donors. Mass cytometry and machine learning pinpointed a novel expanding, population of antigen-specific non-canonical memory CD4+ and CD8+ T cells. B cell sequencing suggested progression from IgM, with apparent cross-reactivity to endemic coronaviruses, to SARS-CoV-2-specific IgA and IgG memory B cells and plasmablasts. Responding lymphocyte populations correlated with eventual SARS-CoV-2 IgG and a donor lacking these cell populations failed to sustain SARS-CoV-2-specific antibodies and experienced breakthrough infection. These integrated proteomic and genomic platforms reveal an antigen-specific cellular basis of RNA vaccine-based immunity.ONE SENTENCE SUMMARYSingle-cell profiling reveals the cellular basis of the antigen-specific response to the BNT162b2 SARS-CoV-2 RNA vaccine.

The antifibrotic therapies nintedanib and pirfenidone were first approved by the United States for the treatment of idiopathic pulmonary fibrosis in 2014. In 2020, nintedanib received U.S. Food and Drug Administration (FDA) approval for the treatment of all progressive fibrosing interstitial lung disease (ILD). Given that a major cause of mortality and morbidity in the idiopathic inflammatory myopathies (IIM) is progressive interstitial lung disease and respiratory failure, antifibrotic therapies may be useful as adjuvant to traditional immunosuppression. However, randomized controlled trials of antifibrotic therapies in IIM are lacking. The purpose of this review is to (1) summarize the mechanism of action of nintedanib and pirfenidone in ILD with possible role in IIM-ILD, (2) review the clinical data supporting their use in interstitial lung disease in general, and more specifically in connective tissue disease associated ILD, and (3) discuss the evidence and remaining challenges for using antifibrotic therapies in IIM-ILD.

ObjectivesThe idiopathic inflammatory myopathies (IIM) are a clinically heterogeneous group of conditions affecting the skin, muscle, joint, and lung in various combinations. This study aims to investigate the immunologic heterogeneity through detailed immunophenotyping of peripheral blood mononuclear cells (PBMCs) in IIM patients and healthy controls.MethodsWe collected PBMCs from 17 patients with a clinical diagnosis of inflammatory myositis in the inpatient or outpatient setting and performed immunophenotyping using mass cytometry by time of flight (CyTOF) to simultaneously characterize B, T, and myeloid cell subsets. Data were analyzed using a combination of supervised biaxial gating and unsupervised clustering algorithms including t-distributed stochastic neighbor embedding (tSNE), cluster identification, characterization, and regression (CITRUS), and marker enrichment modeling (MEM).ResultsWe identified two distinct immune signatures amongst IIM patients. In one signature, increased CD19+CXCR4hiCCR7hi cells correlated with increased CD3+CXCR4hiCD38hi (r=0.62, p=0.009) and CD14+CD16-CXCR4+CD38+HLADR-(r=0.61, p=0.01) populations. In the second signature, increased CD19+CD21loCD11c+ cells correlated with an increased CD3+CD4+PD1+ (r=0.60, p=0.01) population. Other shared immunologic features amongst IIM patients compared to healthy controls included decreased surface expression of RP105/CD180 on B cells (median mass intensity 39.9 ± 16.0 v. 60.9 ± 20.1, p=0.002). In the T cell compartment, all circulating CD3+CXCR3+ subsets (2.7 ± 2.4 v. 9.6 ± 8.1% of all PBMCs, p=0.0004) were reduced.ConclusionBased on circulating B cell phenotype, we identified two distinct immunologic signatures in IIM patients. Future work is needed to determine the significance of these immune signatures for clinical manifestations and treatment responses.

BackgroundRecognition of Anti tRNA synthetase (ARS) related interstitial lung disease (ILD) is key to ensuring patients have prompt access to immunosuppressive therapies. The purpose of this retrospective cohort study was to identify factors that may delay recognition of ARS-ILD.MethodsPatients seen at Vanderbilt University Medical Center (VUMC) between 9/17/2017-10/31/2018 were included in this observational cohort. Clinical and laboratory features were obtained via chart abstraction. Kruskal-Wallis ANOVA, Mann-Whitney U, and Fisher’s exact t tests were utilized to determine statistical significance.ResultsPatients with ARS were found to have ILD in 51.9% of cases, which was comparable to the frequency of ILD in systemic sclerosis (59.5%). The severity of FVC reduction in ARS (53.2%) was comparable to diffuse cutaneous systemic sclerosis (56.8%, p=0.48) and greater than dermatomyositis (66.9%, p=0.005) or limited cutaneous systemic sclerosis (lcSSc, 71.8%, p=0.005). Frank honeycombing was seen with ARS antibodies but not other myositis autoantibodies. ARS patients were more likely to first present to a pulmonary provider in a tertiary care setting (53.6%), likely due to fewer extrapulmonary manifestations. Only 33% of ARS-ILD were anti-nuclear antibody, rheumatoid factor, or anti-cyclic citrullinated peptide positive. Patients with ARS-ILD had a two-fold longer median time to diagnosis compared to other myositis-ILD patients (11.0 months, IQR 8.5 to 43 months vs. 5.0 months, IQR 3.0 to 9.0 months, p=0.003).ConclusionsARS patients without prominent extra-pulmonary manifestations are at high risk for not being recognized as having a connective tissue disease related ILD and miscategorized as UIP/IPF without comprehensive serologies.

Interaction of programmed cell death 1 (PD-1) receptor and its ligand 1 (PD-L1) is well studied in the field of fibrotic lung diseases, supporting its use as a biomarker of progression of interstitial lung disease. Anti PD-L1 therapy has shown effectiveness in improvement of many malignancies and murine models of autoimmune fibrotic lung diseases. Higher PD-1 expression on T cells and PD-L1 expression on human lung fibroblasts are known to contribute towards severity in sarcoidosis and idiopathic pulmonary fibrosis (IPF), respectively. The focus of this investigation was to determine if soluble form of PD-L1 (sPD-L1) serves as predictive biomarker of disease severity in interstitial lung disease (ILD), such as scleroderma, sarcoidosis and IPF. Comparison of local environments, such as bronchoalveolar lavage, revealed significantly higher sPD-L1 levels compared to systemic environments, such as peripheral blood (p=0.001, paired two-tailed Student’s t test). Investigation of serum samples of healthy control, IPF, scleroderma and sarcoidosis patients reveal significantly higher levels in sarcoidosis and IPF patients, compared to patients with scleroderma (p=0.001; p=0.02, one-way ANOVA with Tukey’s respectively). Comparison of serum levels between sarcoidosis patients and healthy controls revealed no significant differences (p=0.09, unpaired two-tailed t test). In addition, comparison of physiologic parameters, such as percent predicated Forced Vital Capacity (FVC) and sPD-L1 levels in sarcoidosis and IPF patients revealed no correlation. These observations suggest that sPD-L1 will not serve as a biomarker of sarcoidosis disease severity. Additional investigation of sPD-L1 in local environments is warranted.

Background The COVID-19 pandemic has overwhelmed hospital systems in multiple countries and necessitated caring for patients in atypical healthcare settings. The goal of this study was to ascertain if the conventional critical care severity scores qSOFA, SOFA, APACHE-II, and SAPS-II could predict which patients admitted to the hospital from an emergency department would eventually require intensive care. Methods This single-center, retrospective cohort study enrolled patients admitted to Vanderbilt University Hospital from the emergency room with symptomatic, confirmed COVID-19 infection between March 8, 2020 through May 15, 2020. Clinical phenotyping was performed by chart abstraction, and the correlation of the qSOFA, SOFA, APACHE-II, and SAPS-II scores for the primary endpoint of ICU admission and secondary endpoint of in-hospital mortality was evaluated. Results During the study period, 128 patients were admitted to Vanderbilt University Hospital from the emergency room with COVID-19. Of these, 39 patients eventually required intensive care; the remaining 89 were discharged from the medical ward. All severity of illness scores demonstrated at least moderate ability to identify patients who would die or require ICU admission. Of the three severity of illness scores assessed, the APACHE-II score performed best with an AUC of 0.851 (95% CI: 0.786 to 0.917) for identifying patient that would require ICU admission. No patient with an APACHE-II score at the time of presentation less than 8 or qSOFA of 0 required intensive care unit (ICU) admission. All patients with an APACHE-II score less than 10 or qSOFA score of 0 survived to hospital discharge. Conclusions The APACHE-II score accurately predicts the eventual need for ICU admission. This may allow for risk-stratification of patients safe to treat in alternative health care settings and prognostic enrichment to accelerate clinical trials of COVID-19 therapies.

Interstitial lung disease (ILD) remains a cause of significant morbidity and mortality in patients with connective tissue disease (CTD)-associated ILD. While some patients meet clear classification criteria for a systemic rheumatic disease, a subset of patients do not meet classification criteria but still benefit from immunosuppressive therapy. In 2015, the American Thoracic Society and European Respiratory Society described classification criteria for interstitial pneumonia with autoimmune features (IPAF) to identify patients with lung-predominant CTD who lack sufficient features of a systemic rheumatic disease to meet classification criteria. Although these criteria are imperfect, they are an important attempt to classify the patient with undifferentiated disease for future study. Rheumatologists play a key role in the evaluation of potential IPAF in patients, especially as many patients with a myositis-spectrum disease (e.g., non-Jo-1 antisynthetase syndrome, anti-melanoma differentiation-associated protein 5 antibody inflammatory myositis, or anti-PM/Scl antibody-associated inflammatory myositis) would be classified under IPAF using the currently available criteria for inflammatory myositis, and would therefore benefit from rheumatologic comanagement. The aim of this review was to describe the historical context that led to the development of these criteria and to discuss the limitations of the current criteria, diagnostic challenges, treatment options, and strategies for disease monitoring.

Human mesenchymal stem/stromal cells (hMSCs) are a promising therapy for acute respiratory distress syndrome (ARDS) and other inflammatory conditions. While considerable research has focused on paracrine effects and mitochondrial transfer that improve lung fluid balance, hMSCs are well known to have immunomodulatory properties as well. Some of these immunomodulatory properties have been related to previously reported paracrine effectors such as indoleamine-2,3-dioxygenase (IDO), but these effects cannot fully account for cell-contact dependent immunomodulation. Here, we report that CD40 is upregulated on hMSCs under the same conditions previously reported to induce IDO. Further, CD40 transcription is also upregulated on hMSCs by ARDS pulmonary edema fluid but not by hydrostatic pulmonary edema fluid. Transcription of CD40, as well as paracrine effectors TSG6 and PTGS2 remained significantly upregulated for at least 12 hours after withdrawal of cytokine stimulation. Finally, induction of this immune phenotype altered the transdifferentiation of hMSCs, one of their hallmark properties. CD40 may play an important role in the immunomodulatory effects of hMSCs in ARDS and inflammation.

Tracheal intubation is common in the care of critically ill adults and is frequently complicated by hypotension, cardiac arrest, or death. We aimed to evaluate administration of an intravenous fluid bolus to prevent cardiovascular collapse during intubation of critically ill adults.We did a pragmatic, multicentre, unblinded, randomised trial in nine sites (eight ICUs and one emergency department) around the USA. Critically ill adults (≥18 years) undergoing tracheal intubation were randomly assigned (1:1, block sizes of 2, 4, and 6, stratified by study site) to either an intravenous infusion of 500 mL of crystalloid solution or no fluid bolus. The primary outcome, assessed in the intention-to-treat population, was cardiovascular collapse, defined as a new systolic blood pressure65 mm Hg; new or increased vasopressor receipt between induction and 2 min after tracheal intubation; or cardiac arrest or death within 1 h of tracheal intubation. Adverse events were assessed in the as-treated population. This trial, which is now complete, is registered with ClinicalTrials.gov, number NCT03026777.Patients were enrolled from Feb 6, 2017, to Jan 9, 2018, when the data and safety monitoring board stopped the trial on the basis of futility. By trial termination, 337 (63%) of 537 screened adults had been randomly assigned. Cardiovascular collapse occurred in 33 (20%) of 168 patients in the fluid bolus group compared with 31 (18%) of 169 patients in the no fluid bolus group (absolute difference 1·3% [95% CI -7·1% to 9·7%]; p=0·76). The individual components of the cardiovascular collapse composite outcome did not differ between groups (new systolic blood pressure65 mm Hg 11 [7%] in the bolus group vs ten [6%] in the no-bolus group, new or increased vasopressor 32 [19%] vs 31 [18%], cardiac arrest within 1 h seven [4%] vs two [1%], death within 1 h of intubation two [1%] vs one [1%]). In-hospital mortality was not significantly different in the fluid bolus group (48 [29%]) compared with no fluid bolus (59 [35%]).Administration of an intravenous fluid bolus did not decrease the overall incidence of cardiovascular collapse during tracheal intubation of critically ill adults compared with no fluid bolus in this trial.US National Institutes of Health.

Data on interstitial lung disease (ILD) outcomes in the intensive care unit (ICU) is of limited value due to population heterogeneity. The aim of this study was to examine risk factors for mortality and ILD mortality rates in the ICU.We performed a systematic review using five databases. 50 studies were identified and 34 were included: 17 studies on various aetiologies of ILD (mixed-ILD) and 17 on idiopathic pulmonary fibrosis (IPF). In mixed-ILD, elevated APACHE score, hypoxaemia and mechanical ventilation are risk factors for mortality. No increased mortality was found with steroid use. Evidence is inconclusive on advanced age. In IPF, evidence is inconclusive for all factors except mechanical ventilation and hypoxaemia. The overall in-hospital mortality was available in 15 studies on mixed-ILD (62% in 2001–2009 and 48% in 2010–2017) and 15 studies on IPF (79% in 1993–2004 and 65% in 2005–2017). Follow-up mortality rate at 1 year ranged between 53% and 100%.Irrespective of ILD aetiology, mechanical ventilation is associated with increased mortality. For mixed-ILD, hypoxaemia and APACHE scores are also associated with increased mortality. IPF has the highest mortality rate among ILDs, but since 1993 the rate appears to be declining. Despite improving in-hospital survival, overall mortality remains high.

The acute respiratory distress syndrome (ARDS) is common in critically ill patients and has a high mortality rate. Mesenchymal stromal cells (MSCs) have demonstrated therapeutic potential in animal models of ARDS, and their benefits occur in part through interactions with alveolar type II (ATII) cells. However, the effects that MSCs have on human ATII cells have not been well studied. Using previously published microarray data, we performed genome‐wide differential gene expression analyses of human ATII cells that were (1) unstimulated, (2) exposed to proinflammatory cytokines (CytoMix), or (3) exposed to proinflammatory cytokines plus MSCs. Findings were validated by qPCR. Alveolar type II cells differentially expressed hundreds of genes when exposed either to proinflammatory cytokines or to proinflammatory cytokines plus MSCs. Stimulation with proinflammatory cytokines increased expression of inflammatory genes and downregulated genes related to surfactant function and alveolar fluid clearance. Some of these changes, including expression of some cytokines and genes related to surfactant, were reversed by exposure to MSCs. In addition, MSCs induced upregulation of other potentially beneficial genes, such as those related to extracellular matrix remodeling. We confirmed several of these gene expression changes by qPCR. Thus, ATII cells downregulate genes associated with surfactant and alveolar fluid clearance when exposed to inflammatory cytokines, and mesenchymal stromal cells partially reverse many of these gene expression changes.

Systemic sclerosis (SSc) is a devastating autoimmune disease characterized by fibrosis of the skin and vital organs. The pathogenesis of SSc is unknown, but detection of autoantibodies in >90% of SSc patients suggests that B lymphocytes play a role. Therefore, we explored B cell phenotypes in SSc patients using fluorescence cytometry and the multi-dimensional unsupervised analysis tool viSNE. We found that compared to healthy controls, SSc patients had significantly higher proportions of an autoreactive-prone B cell subset identified by low expression of CD21 (CD21lo). Previously, circulating CD21lo B cells were shown to express autoantibodies and were increased in other autoimmune diseases. When considering the clinical phenotypes of the SSc patients, we found that the frequency of CD21lo B cells was only increased in SSc patients with interstitial lung disease (ILD). ILD is a complication of SSc that is associated with increased morbidity and mortality. To our knowledge, this is the first time that a peripheral blood B cell subset has been identified in association with ILD in patients with a systemic autoimmune disease. We investigated the signaling properties of these anergic cells and found lower expression of Bruton’s tyrosine kinase (BTK) in CD21lo B cells compared to normal B cells. This was surprising, as BTK is thought to be overexpressed in autoimmunity, but may indicate that the anergic state is due in part to suppression of BTK-mediated signaling. Our data suggest that CD21lo B cells should be investigated for their role in SSc pathogenesis, and for their utility as a biomarker of ILD. In addition, these findings demonstrate a potential mechanism by which B cell depleting therapy may specifically benefit SSc patients with ILD.

The systemic vasculitides are a diverse set of diseases linked by the presence of blood-vessel inflammation and are often associated with life-threatening or critical complications, including glomerulonephritis, diffuse alveolar haemorrhage, pulmonary arterial hypertension and airway compromise. The protean manifestations of the systemic vasculitides make them challenging to diagnose. Early recognition, however, is crucial to improving outcomes. This article serves as an introduction to these complex diseases, reviewing the manifestations of systemic vasculitis that may be encountered in an intensive care setting, and outlines an overall approach to their treatment.

Fragment based drug discovery remains a successful tool for pharmaceutical lead discovery. Although based upon the principle of thermodynamic additivity, the underlying thermodynamic basis is poorly understood. A thermodynamic additivity analysis was performed using stromelysin-1 and a series of biphenyl hydroxamate ligands identified through fragment additivity. Our studies suggest that, in this instance, additivity arises from enthalpic effects, while interaction entropies are unfavorable; this thermodynamic behavior is masked by proton transfer. Evaluation of the changes in constant pressure heat capacities during binding suggest that solvent exclusion from the binding site does not account for the dramatic affinity enhancements observed.

In recent years, interfacial mobility has gained popularity as a model with which to rationalize both affinity in ligand binding and the often observed phenomenon of enthalpy-entropy compensation. While protein contraction and reduced mobility, as demonstrated by computational and NMR techniques respectively, have been correlated to entropies of binding for a variety of systems, to our knowledge, Raman difference spectroscopy has never been included in these analyses. Here, non-resonance Raman difference spectroscopy, isothermal titration calorimetry, and x-ray crystallography were utilized to correlate protein contraction, as demonstrated by an increase in protein interior packing and decreased residual protein movement, with trends of enthalpy-entropy compensation. These results are in accord with the interfacial mobility model, and lend additional credence to this view of protein activity.

We describe a novel single-step method for the purification of stromelysin-1 catalytic domain (SCD) via immobilized metal affinity chromatography under denaturing conditions that inhibit proteolytic activity followed by on-column refolding and spontaneous autolysis of the fusion peptide to yield pure, active stromelysin-1 catalytic domain. The methodology provides a general approach for the rapid purification of large quantities of zinc proteinases.