The orally bioavailable GSPT1/2 degrader SJ6986 exhibits in vivo efficacy in acute lymphoblastic leukemia.

Advancing cure rates for high-risk acute lymphoblastic leukemia (ALL) has been limited by the lack of agents that effectively kill leukemic cells, sparing normal hematopoietic tissue. Molecular glues direct the ubiquitin ligase cellular machinery to target neosubstrates for protein degradation. We developed a novel cereblon modulator, SJ6986, that exhibits potent and selective degradation of GSPT1 and GSPT2 and cytotoxic activity against childhood cancer cell lines. Here, we report in vitro and in vivo testing of the activity of this agent in a panel of ALL cell lines and xenografts. SJ6986 exhibited similar cytotoxicity to the previously described GSPT1 degrader CC-90009 in a panel of leukemia cell lines in vitro, resulting in apoptosis and perturbation of cell cycle progression. SJ6986 was more effective than CC-90009 in suppressing leukemic cell growth in vivo, partly attributable to favorable pharmacokinetic properties, and did not significantly impair differentiation of human CD34+ cells ex vivo. Genome-wide CRISPR/Cas9 screening of ALL cell lines treated with SJ6986 confirmed that components of the CRL4CRBN complex, associated adaptors, regulators, and effectors were integral in mediating the action of SJ6986. SJ6986 is a potent, selective, orally bioavailable GSPT1/2 degrader that shows broad antileukemic activity and has potential for clinical development.

Clinical course and follow-up of pediatric patients with COVID-19 vaccine-associated myocarditis compared to non-vaccine-associated myocarditis within the prospective multicenter registry-"MYKKE".

BACKGROUND: Since the onset of widespread COVID-19 vaccination, increased incidence of COVID-19 vaccine-associated myocarditis (VA-myocarditis) has been noted, particularly in male adolescents. METHODS: Patients <18 years with suspected myocarditis following COVID-19 vaccination within 21 days were enrolled in the PedMYCVAC cohort, a substudy within the prospective multicenter registry for pediatric myocarditis "MYKKE." Clinical data at initial admission, 3- and 9-months follow-up were monitored and compared to pediatric patients with confirmed non-vaccine-associated myocarditis (NVA-myocarditis) adjusting for various baseline characteristics. RESULTS: From July 2021 to December 2022, 56 patients with VA-myocarditis across 15 centers were enrolled (median age 16.3 years, 91% male). Initially, 11 patients (20%) had mildly reduced left ventricular ejection fraction (LVEF; 45%-54%). No incidents of severe heart failure, transplantation or death were observed. Of 49 patients at 3-months follow-up (median (IQR) 94 (63-118) days), residual symptoms were registered in 14 patients (29%), most commonly atypical intermittent chest pain and fatigue. Diagnostic abnormalities remained in 23 patients (47%). Of 21 patients at 9-months follow-up (259 (218-319) days), all were free of symptoms and diagnostic abnormalities remained in 9 patients (43%). These residuals were mostly residual late gadolinium enhancement in magnetic resonance imaging. Patients with NVA-myocarditis (n=108) more often had symptoms of heart failure (P = .003), arrhythmias (P = .031), left ventricular dilatation (P = .045), lower LVEF (P < .001) and major cardiac adverse events (P = .102). CONCLUSIONS: Course of COVID-19 vaccine-associated myocarditis in pediatric patients seems to be mild and differs from non-vaccine-associated myocarditis. Due to a considerable number of residual symptoms and diagnostic abnormalities at follow-up, further studies are needed to define its long-term implications.

Psychosocial burden and quality of life of parents with children with univentricular hearts compared to ASD parents and parents of heart-healthy children.

BACKGROUND: Patients with univentricular hearts can only be palliated by a staged surgical procedure that carries a high morbidity and mortality risk. The aim of this study was to examine the emotional demands, psychosocial burden, and quality of life of parents with children with univentricular hearts compared to parents of children with a simple heart defect, those with no heart defect and children with chronic diseases. METHODS: An anonymous questionnaire was created to interview parents about their quality of life, stressors, needs, strategies for coping with illness, and partnership satisfaction. RESULTS: 73 families participated in the study. Parents of children with univentricular hearts experience a significantly higher psychosocial burden, limitations in daily life, and distress in family interactions, as well as greater emotional distress compared to the other study groups. When comparing the families of children with other chronic diseases (e.g. cystic fibrosis, chronic arthritis and diabetes), these differences remained significant. CONCLUSION: The study confirms a higher psychosocial burden, restrictions in daily life and a lower quality of life of parents with children with univentricular hearts, compared to parents of children with simple heart defects and parents of heart-healthy children or those with other chronic diseases. Since this condition persists until adolescence and adulthood, the families are exposed to special challenges and stresses throughout their lives. This has yet to be adequately addressed in the management of these families.

Macromolecular room temperature crystallography.

X-ray crystallography enables detailed structural studies of proteins to understand and modulate their function. Conducting crystallographic experiments at cryogenic temperatures has practical benefits but potentially limits the identification of functionally important alternative protein conformations that can be revealed only at room temperature (RT). This review discusses practical aspects of preparing, acquiring, and analyzing X-ray crystallography data at RT to demystify preconceived impracticalities that freeze progress of routine RT data collection at synchrotron sources. Examples are presented as conceptual and experimental templates to enable the design of RT-inspired studies; they illustrate the diversity and utility of gaining novel insights into protein conformational landscapes. An integrative view of protein conformational dynamics enables opportunities to advance basic and biomedical research.

Activation of the integrated stress response rewires cardiac metabolism in Barth syndrome.

Barth Syndrome (BTHS) is an inherited cardiomyopathy caused by defects in the mitochondrial transacylase TAFAZZIN (Taz), required for the synthesis of the phospholipid cardiolipin. BTHS is characterized by heart failure, increased propensity for arrhythmias and a blunted inotropic reserve. Defects in Ca2+-induced Krebs cycle activation contribute to these functional defects, but despite oxidation of pyridine nucleotides, no oxidative stress developed in the heart. Here, we investigated how retrograde signaling pathways orchestrate metabolic rewiring to compensate for mitochondrial defects. In mice with an inducible knockdown (KD) of TAFAZZIN, and in induced pluripotent stem cell-derived cardiac myocytes, mitochondrial uptake and oxidation of fatty acids was strongly decreased, while glucose uptake was increased. Unbiased transcriptomic analyses revealed that the activation of the eIF2α/ATF4 axis of the integrated stress response upregulates one-carbon metabolism, which diverts glycolytic intermediates towards the biosynthesis of serine and fuels the biosynthesis of glutathione. In addition, strong upregulation of the glutamate/cystine antiporter xCT increases cardiac cystine import required for glutathione synthesis. Increased glutamate uptake facilitates anaplerotic replenishment of the Krebs cycle, sustaining energy production and antioxidative pathways. These data indicate that ATF4-driven rewiring of metabolism compensates for defects in mitochondrial uptake of fatty acids to sustain energy production and antioxidation.

Degradation of Janus kinases in CRLF2-rearranged acute lymphoblastic leukemia.

CRLF2-rearranged (CRLF2r) acute lymphoblastic leukemia (ALL) accounts for more than half of Philadelphia chromosome-like (Ph-like) ALL and is associated with a poor outcome in children and adults. Overexpression of CRLF2 results in activation of Janus kinase (JAK)-STAT and parallel signaling pathways in experimental models, but existing small molecule inhibitors of JAKs show variable and limited efficacy. Here, we evaluated the efficacy of proteolysis-targeting chimeras (PROTACs) directed against JAKs. Solving the structure of type I JAK inhibitors ruxolitinib and baricitinib bound to the JAK2 tyrosine kinase domain enabled the rational design and optimization of a series of cereblon (CRBN)-directed JAK PROTACs utilizing derivatives of JAK inhibitors, linkers, and CRBN-specific molecular glues. The resulting JAK PROTACs were evaluated for target degradation, and activity was tested in a panel of leukemia/lymphoma cell lines and xenograft models of kinase-driven ALL. Multiple PROTACs were developed that degraded JAKs and potently killed CRLF2r cell lines, the most active of which also degraded the known CRBN neosubstrate GSPT1 and suppressed proliferation of CRLF2r ALL in vivo, e.g. compound 7 (SJ988497). Although dual JAK/GSPT1-degrading PROTACs were the most potent, the development and evaluation of multiple PROTACs in an extended panel of xenografts identified a potent JAK2-degrading, GSPT1-sparing PROTAC that demonstrated efficacy in the majority of kinase-driven xenografts that were otherwise unresponsive to type I JAK inhibitors, e.g. compound 8 (SJ1008030). Together, these data show the potential of JAK-directed protein degradation as a therapeutic approach in JAK-STAT-driven ALL and highlight the interplay of JAK and GSPT1 degradation activity in this context.

Tricuspid Annular Plane Systolic Excursion (TAPSE) correlates with mean pulmonary artery pressure especially 10 years after pediatric heart transplantation.

Tricuspid annular plane systolic excursion (TAPSE) is important in the noninvasive echocardiographic assessment of right heart function. This retrospective observational study shows correlations of TAPSE with invasive right heart catheterization parameters after pediatric heart transplantation (HTx). The study included patients after pediatric HTx with cardiac catheterizations in 2018/2019 and measurement of TAPSE (n = 52 patients with 57 examinations; 50.9% adults, 52.6% female, median age: 18.54 years). TAPSE was compared with normal values. Stepwise, linear and multiple regression were used to show influencing variables on TAPSE. Mean TAPSE z-score was -3.48 (SD: 2.25) and 68.4% of HTx-recipients showed abnormally reduced TAPSE (z-score ←2) compared to normal values. Multiple regression (p-value <0.001; corrected R2 = 0.338) showed significant correlations of time since HTx (p-value <0.001) and mPAP (p-value: 0.008) with TAPSE z-scores. Divided into subgroups (time since HTx <10 and ≥10 years), TAPSE and mPAP correlated only ≥10 years after HTx (p-value = 0.002). This study provides data of TAPSE even ≥10 years after pediatric HTx. Most patients showed a decreased TAPSE early after HTx, which improved over time. TAPSE z-scores correlated significantly with time since HTx and mPAP, especially ≥10 years post-HTx. Therefore, TAPSE must be used carefully in the early follow-up.

Intratumoural heterogeneity generated by Notch signalling promotes small-cell lung cancer.

The Notch signalling pathway mediates cell fate decisions and is tumour suppressive or oncogenic depending on the context. During lung development, Notch pathway activation inhibits the differentiation of precursor cells to a neuroendocrine fate. In small-cell lung cancer, an aggressive neuroendocrine lung cancer, loss-of-function mutations in NOTCH genes and the inhibitory effects of ectopic Notch activation indicate that Notch signalling is tumour suppressive. Here we show that Notch signalling can be both tumour suppressive and pro-tumorigenic in small-cell lung cancer. Endogenous activation of the Notch pathway results in a neuroendocrine to non-neuroendocrine fate switch in 10-50% of tumour cells in a mouse model of small-cell lung cancer and in human tumours. This switch is mediated in part by Rest (also known as Nrsf), a transcriptional repressor that inhibits neuroendocrine gene expression. Non-neuroendocrine Notch-active small-cell lung cancer cells are slow growing, consistent with a tumour-suppressive role for Notch, but these cells are also relatively chemoresistant and provide trophic support to neuroendocrine tumour cells, consistent with a pro-tumorigenic role. Importantly, Notch blockade in combination with chemotherapy suppresses tumour growth and delays relapse in pre-clinical models. Thus, small-cell lung cancer tumours generate their own microenvironment via activation of Notch signalling in a subset of tumour cells, and the presence of these cells may serve as a biomarker for the use of Notch pathway inhibitors in combination with chemotherapy in select patients with small-cell lung cancer.

Transient Recurrent Laryngeal Nerve Palsy after Interventional Therapy.

BACKGROUND: Hoarseness due to laryngeal nerve injury is a known complication after cardiothoracic surgery involving the aortic arch. However, this complication is only rarely reported after catheter interventions. RESULTS: In this article we present the unusual case of a left-sided vocal cord paralysis in four patients after primary stenting of a re-coarctation, re-dilatation of a stented coarctation, a primary stenting of the left pulmonary artery (LPA), and prestenting for percutaneous pulmonary valve implantation with dilation of the LPA. After implanting bare metal stents, it is common practice, whilst contemplating the diameters of the adjacent structures, to optimize the stent diameter in a two-step procedure and dilate the stent until a maximum diameter is achieved and there is no residual gradient after applying this technique. Four of our patients experienced hoarseness after the intervention and a vocal cord paralysis was diagnosed. Angiography revealed no signs of extravasation or dissection. Clinical symptoms improved over the course of the following 6 months; patients with interventions at the aortic arch showed a complete remission, patients with procedures involving the LPA showed only mild regression of the symptoms. CONCLUSION: To our knowledge, this complication (Ortner's syndrome, cardiovocal syndrome) after such interventions has rarely been reported before. Although a rare complication, the recognition of these symptoms may support colleagues in managing affected patients. In addition, awareness for hoarseness after interventional therapies and systematic screening for this complication might help to identify patients at risk in the future.

[Chest pain and cardiovascular diseases in women : Diagnostics and treatment]. / Brustschmerz und kardiovaskuläre Erkrankungen bei Frauen : Diagnostik und Therapie.

Cardiovascular diseases (CVD) are the leading cause of global mortality not only in men but also in women. The incidence of CVD significantly increases in women, especially after the menopause. Sex and gender differences in the incidence, prevalence and mortality of CVD are due to hormonal, anatomical, and sociocultural differences. As part of the primary and secondary prevention of coronary heart disease (CHD), risk factors specific for women, such as autoimmune diseases and pregnancy-associated diseases (e.g., gestational diabetes and pre-eclampsia) should also be taken into account in addition to the classical cardiovascular risk factors. Furthermore, in women with angina pectoris it should be considered that women in particular frequently suffer from ischemia with nonobstructive coronary arteries (INOCA) that can be caused, for example, by coronary microvascular dysfunction (CMD) or coronary spasms. Based on this, the diagnostics should not be terminated in symptomatic women after coronary angiography with normal epicardial vessels. A targeted diagnostics for CMD and coronary spasms should be carried out at an early stage.

Ticagrelor or Prasugrel in Patients with Acute Coronary Syndromes.

BACKGROUND: The relative merits of ticagrelor as compared with prasugrel in patients with acute coronary syndromes for whom invasive evaluation is planned are uncertain. METHODS: In this multicenter, randomized, open-label trial, we randomly assigned patients who presented with acute coronary syndromes and for whom invasive evaluation was planned to receive either ticagrelor or prasugrel. The primary end point was the composite of death, myocardial infarction, or stroke at 1 year. A major secondary end point (the safety end point) was bleeding. RESULTS: A total of 4018 patients underwent randomization. A primary end-point event occurred in 184 of 2012 patients (9.3%) in the ticagrelor group and in 137 of 2006 patients (6.9%) in the prasugrel group (hazard ratio, 1.36; 95% confidence interval [CI], 1.09 to 1.70; P = 0.006). The respective incidences of the individual components of the primary end point in the ticagrelor group and the prasugrel group were as follows: death, 4.5% and 3.7%; myocardial infarction, 4.8% and 3.0%; and stroke, 1.1% and 1.0%. Definite or probable stent thrombosis occurred in 1.3% of patients assigned to ticagrelor and 1.0% of patients assigned to prasugrel, and definite stent thrombosis occurred in 1.1% and 0.6%, respectively. Major bleeding (as defined by the Bleeding Academic Research Consortium scale) was observed in 5.4% of patients in the ticagrelor group and in 4.8% of patients in the prasugrel group (hazard ratio, 1.12; 95% CI, 0.83 to 1.51; P = 0.46). CONCLUSIONS: Among patients who presented with acute coronary syndromes with or without ST-segment elevation, the incidence of death, myocardial infarction, or stroke was significantly lower among those who received prasugrel than among those who received ticagrelor, and the incidence of major bleeding was not significantly different between the two groups. (Funded by the German Center for Cardiovascular Research and Deutsches Herzzentrum München; ISAR-REACT 5 ClinicalTrials.gov number, NCT01944800.).

[Novel options to maximize oral lipid lowering treatment : Role of bempedoic acid in combination treatment]. / Neue Optionen zur Intensivierung der lipidsenkenden Therapie : Rolle von Bempedoinsäure in der Kombinationstherapie.

Epidemiological, randomized, controlled, clinical and genetic studies confirm that low-density lipoprotein cholesterol (LDL-C) is a causative factor for atherosclerotic diseases. The current European Society of Cardiology and European Atherosclerosis Society (ESC/EAS) guidelines on the management of dyslipidemia recommend a target LDL-C < 55 mg/dl and at least a 50% reduction in baseline LDL­C for high-risk patients; however, these target values are often not achieved in routine clinical practice, as shown by recent cross-sectional data from EUROASPIRE or DaVinci. Therefore, combination treatment is recommended, which, as with treatment of blood pressure, can improve the success of treatment. Bempedoic acid is a new substance, which is suitable for combination treatment and represents an alternative particularly for patients with statin-associated muscular symptoms. Bempedoic acid reduces LDL­C by approximately 25% in statin-naïve patients and by some 18% in addition to statins. In a fixed doses combination with ezetimibe, bempedoic acid can lower LDL­C by up to 45% in statin-naïve patients and by 38% (placebo-corrected) in addition to statins. Bempedoic acid is generally very well tolerated: however, it can lead to a reversible increase in uric acid. Occasionally, a slight decrease in hemoglobin has been documented. Therefore, it is recommended that not only changes in lipid levels but also uric acid and hematological parameters should be monitored in the first 3 months.

Water Networks Repopulate Protein-Ligand Interfaces with Temperature.

High-resolution crystal structures highlight the importance of water networks in protein-ligand interactions. However, as these are typically determined at cryogenic temperature, resulting insights may be structurally precise but not biologically accurate. By collecting 10 matched room-temperature and cryogenic datasets of the biomedical target Hsp90α, we identified changes in water networks that impact protein conformations at the ligand binding interface. Water repositioning with temperature repopulates protein ensembles and ligand interactions. We introduce Flipper conformational barcodes to identify temperature-sensitive regions in electron density maps. This revealed that temperature-responsive states coincide with ligand-responsive regions and capture unique binding signatures that disappear upon cryo-cooling. Our results have implications for discovering Hsp90 selective ligands, and, more generally, for the utility of hidden protein and water conformations in drug discovery.

Conversion to everolimus in pediatric heart transplant recipients is a safe treatment option with an impact on cardiac allograft vasculopathy and renal function.

BACKGROUND: Cardiac allograft vasculopathy (CAV) and nephrotoxicity affect long-term survival after heart transplantation (HTX). Studies, mostly conducted in adults, showed a positive effect of everolimus (EVL) on these problems. We describe the effects of conversion of the immunosuppressive therapy to an everolimus including regime on CAV, renal function, and safety in heart transplanted children/adolescents. METHODS: This retrospective single-center study included 36 participants (mean time after HTX 6.3 ± 4.7 years). Descriptive pre/post-comparisons were performed with an observation period partially up to 4 years. Impact on CAV was assessed based on intravascular imaging and Stanford grading. Safety analysis included cytomegalovirus (CMV)-infection and acute rejection. RESULTS: In terms of CAV (9 out of 36 patients) four showed no progression, three an improvement, one a worsening; one new diagnosis. The average CrCl showed a significant improvement 6, 12, and 24 months after conversion regarding all patients (n = 29). There was no acute rejection or CMV-infection. CONCLUSION: Conversion to an EVL-based therapy after pediatric HTX is a safe immunosuppressive regime without increasing risk of acute rejection or CMV-infection. There was some evidence of reduction in progression of CAV and a significant improvement of the renal function.

Quality of life and patient satisfaction with outpatient care after heart transplantation in adult and pediatric patients - room for improvement?

Reduced adherence after heart transplantation increases the risk for acute rejection. Therefore, the aim of this study was to evaluate the patient's satisfaction with outpatient care and quality of life (QOL) after pediatric and adult heart transplantation. Observational study after pediatric (n = 22) and adult (n = 65) heart transplantation and the parents of the pediatric patients (n = 22) to evaluate the patients' satisfaction with outpatient care and QOL. Established standardized questionnaires were used for patient satisfaction (ZAP survey) and QOL (SF36); the latter was compared with the cohort of the BGS98 survey (BGS98 cohort). ZAP score: excellent results with almost all values >80. QOL: pediatric cohort showed significantly higher values in physical functioning (P = 0.041) and role physical (P = 0.003) but significantly lower values in the sub-scale general health (P = 0.02) compared to adult cohort. In comparison with BGS98 cohort, children showed almost similar results, whereas adult cohort showed worse values in physical and emotional functioning, but higher values regarding general health. The QOL of patients after pediatric heart transplantation is comparable to a standardized reference population in Germany, whereas adult patients show reduced physical and emotional functioning, but better values regarding general health. The patients' satisfaction with the outpatient care is very high.

Phenyl-Glutarimides: Alternative Cereblon Binders for the Design of PROTACs.

Targeting cereblon (CRBN) is currently one of the most frequently reported proteolysis-targeting chimera (PROTAC) approaches, owing to favorable drug-like properties of CRBN ligands, immunomodulatory imide drugs (IMiDs). However, IMiDs are known to be inherently unstable, readily undergoing hydrolysis in body fluids. Here we show that IMiDs and IMiD-based PROTACs rapidly hydrolyze in commonly utilized cell media, which significantly affects their cell efficacy. We designed novel CRBN binders, phenyl glutarimide (PG) analogues, and showed that they retained affinity for CRBN with high ligand efficiency (LE >0.48) and displayed improved chemical stability. Our efforts led to the discovery of PG PROTAC 4 c (SJ995973), a uniquely potent degrader of bromodomain and extra-terminal (BET) proteins that inhibited the viability of human acute myeloid leukemia MV4-11 cells at low picomolar concentrations (IC50 =3 pM; BRD4 DC50 =0.87 nM). These findings strongly support the utility of PG derivatives in the design of CRBN-directed PROTACs.

N-acety-b-D-glucosaminidase: A potential biomarker for early detection of acute kidney injury in acute chest pain.

AIM: Acute kidney injury (AKI) is often underdiagnosed due to several limitations of the renal marker creatinine. Tubular urinary biomarkers may substantially contribute to diagnose AKI early. For early detection of AKI, we evaluated for the first time N-acetyl-ß-d-glucosaminidase (NAG), Kidney-injury-molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) in acute chest pain. METHODS: We included 402 chest pain patients aged 18 to 95 years seen in the emergency department. From 311 subjects, blood and urine samples were collected. RESULTS: Thirty-three patients developed an AKI and showed a significant increase in all three tubular markers compared to patients without AKI (each P < .001). According to receiver operating characteristic (ROC) analysis, combining NAG and creatinine showed a significantly increased area under the curve (AUC) compared to creatinine alone (AUC: 0.75 vs 0.87; P < .001). KIM-1, NGAL and cystatin C showed no significant differences in AUC compared to creatinine. In 120 individuals with blood and urine sampling before contrast media exposure, ROC analysis showed a significantly improved diagnostic performance for the combination of both (AUC: 0.83 vs creatinine AUC: 0.66; P = .004). AKI occurrence showed no dependency from CM volume. NAG presented as an independent AKI predictor beside creatinine, age, the diagnosis of myocardial infarction and mean arterial pressure. Regarding the prognostic value for renal replacement therapy, the combination of NAG and creatinine showed a significantly lager AUC than creatinine (AUC: 0.95 vs AUC: 0.85; P < .001). CONCLUSION: NAG presented as a promising marker of impending AKI and the necessity of renal replacement therapy.

Testing inhomogeneous solvation theory in structure-based ligand discovery.

Binding-site water is often displaced upon ligand recognition, but is commonly neglected in structure-based ligand discovery. Inhomogeneous solvation theory (IST) has become popular for treating this effect, but it has not been tested in controlled experiments at atomic resolution. To do so, we turned to a grid-based version of this method, GIST, readily implemented in molecular docking. Whereas the term only improves docking modestly in retrospective ligand enrichment, it could be added without disrupting performance. We thus turned to prospective docking of large libraries to investigate GIST's impact on ligand discovery, geometry, and water structure in a model cavity site well-suited to exploring these terms. Although top-ranked docked molecules with and without the GIST term often overlapped, many ligands were meaningfully prioritized or deprioritized; some of these were selected for testing. Experimentally, 13/14 molecules prioritized by GIST did bind, whereas none of the molecules that it deprioritized were observed to bind. Nine crystal complexes were determined. In six, the ligand geometry corresponded to that predicted by GIST, for one of these the pose without the GIST term was wrong, and three crystallographic poses differed from both predictions. Notably, in one structure, an ordered water molecule with a high GIST displacement penalty was observed to stay in place. Inclusion of this water-displacement term can substantially improve the hit rates and ligand geometries from docking screens, although the magnitude of its effects can be small and its impact in drug binding sites merits further controlled studies.

Water Networks Can Determine the Affinity of Ligand Binding to Proteins.

Solvent organization is a key but underexploited contributor to the thermodynamics of protein-ligand recognition, with implications for ligand discovery, drug resistance, and protein engineering. Here, we explore the contribution of solvent to ligand binding in the Haemophilus influenzae virulence protein SiaP. By introducing a single mutation without direct ligand contacts, we observed a >1000-fold change in sialic acid binding affinity. Crystallographic and calorimetric data of wild-type and mutant SiaP showed that this change results from an enthalpically unfavorable perturbation of the solvent network. This disruption is reflected by changes in the normalized atomic displacement parameters of crystallographic water molecules. In SiaP's enclosed cavity, relative differences in water-network dynamics serve as a simple predictor of changes in the free energy of binding upon changing protein, ligand, or both. This suggests that solvent structure is an evolutionary constraint on protein sequence that contributes to ligand affinity and selectivity.