Understanding Attachment, Emotional Regulation, and Childhood Adversity and Their Link to Chemsex.

Background: Although evidence shows that engaging in chemsex can be associated with poor mental health, little is known about the relationship between psychological factors and this type of drug use. We aim to explore associations between engagement in chemsex and several psychological variables (adverse life events, attachment styles, emotional regulation skills, self-care patterns) in a sample of gay, bisexual, and other men who have sex with men (GBMSM) with drug-related problems. Methods: A group of GBMSM engaged in chemsex (n = 41) and a control group of GBMSM (n = 39) completed an online survey to assess drug-related problems and the abovementioned psychological variables, in which both groups were compared. All analyses were adjusted for covariates showing significant differences between groups. Results: Compared to the control group, participants engaged in chemsex showed significantly higher frequencies of an avoidant-insecure attachment style and early adverse life events, regardless of all covariates (HIV status, job situation, and place of birth). Poorer emotional regulation and self-care patterns and a higher frequency of sexual abuse were also found in participants engaged in chemsex, though we cannot rule out the influence of HIV status on this second group of variables. Conclusions: Some people with drug-related problems engaged in chemsex might have suffered early adverse events and might have an avoidant-insecure attachment style. Moreover, those who have been diagnosed with HIV might show higher emotional dysregulation and poorer self-care patterns. These variables should be routinely evaluated in this population.

Molecular magnetic resonance imaging discloses endothelial activation after transient ischaemic attack.

SEE SUN ET AL DOI101093/AWW306 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: About 20% of patients with ischaemic stroke have a preceding transient ischaemic attack, which is clinically defined as focal neurological symptoms of ischaemic origin resolving spontaneously. Failure to diagnose transient ischaemic attack is a wasted opportunity to prevent recurrent disabling stroke. Unfortunately, diagnosis can be difficult, due to numerous mimics, and to the absence of a specific test. New diagnostic tools are thus needed, in particular for radiologically silent cases, which correspond to the recommended tissue-based definition of transient ischaemic attack. As endothelial activation is a hallmark of cerebrovascular events, we postulated that this may also be true for transient ischaemic attack, and that it would be clinically relevant to develop non-invasive in vivo imaging to detect this endothelial activation. Using transcriptional and immunohistological analyses for adhesion molecules in a mouse model, we identified brain endothelial P-selectin as a potential biomarker for transient ischaemic attack. We thus developed ultra-sensitive molecular magnetic resonance imaging using antibody-based microparticles of iron oxide targeting P-selectin. This highly sensitive imaging strategy unmasked activated endothelial cells after experimental transient ischaemic attack and allowed discriminating transient ischaemic attack from epilepsy and migraine, two important transient ischaemic attack mimics. We provide preclinical evidence that combining conventional magnetic resonance imaging with molecular magnetic resonance imaging targeting P-selectin might aid in the diagnosis of transient ischaemic attack.

Chemsex. An emergent phenomenon. / Chemsex. Un fenómeno emergente.

Letter to the editor.

Carta al editor.

Copeptin and Long-Term Risk of Recurrent Vascular Events After Transient Ischemic Attack and Ischemic Stroke: Population-Based Study.

BACKGROUND AND PURPOSE: Copeptin, the c-terminal portion of provasopressin, is a useful prognostic marker in patients after myocardial infarction and heart failure. More recently, high levels of copeptin have also been associated with worse functional outcome and increased mortality within the first year after ischemic stroke and transient ischemic attack (TIA). However, to date, there are no published data on whether copeptin predicts long-term risk of vascular events after TIA and stroke. METHODS: We measured copeptin levels in consecutive patients with TIA or ischemic stroke in a population-based study (Oxford Vascular Study) recruited from 2002 to 2007 and followed up to 2014. Associations with risk of recurrent vascular events were determined by Cox-regression. RESULTS: During ≈6000 patient-years in 1076 patients, there were 357 recurrent vascular events, including 174 ischemic strokes. After adjustment for age, sex, and risk factors, copeptin was predictive of recurrent vascular events (adjusted hazard ratio per SD, 1.47; 95% confidence interval, 1.31-1.64; P=0.0001), vascular death (1.85; 1.60-2.14; P<0.0001), all-cause death (1.75; 1.58-1.93; P<0.0001), and recurrent ischemic stroke (1.22; 1.04-1.44; P=0.017); and improved model-discrimination significantly: net reclassification improvement for recurrent vascular events (32%; P<0.0001), vascular death (55%; P<0.0001), death (66%; P<0.0001), and recurrent stroke (16%; P=0.044). The predictive value of copeptin was largest in patients with cardioembolic index events (adjusted hazard ratio, 1.84; 95% confidence interval, 1.53-2.20 versus 1.31, 1.14-1.50 in noncardioembolic stroke; P=0.0025). In patients with cardioembolic stroke, high copeptin levels were associated with a 4-fold increased risk of vascular events within the first year of follow-up (adjusted hazard ratio, 4.02; 95% confidence interval, 2.13-7.70). CONCLUSIONS: In patients with TIA and ischemic stroke, copeptin predicted recurrent vascular events and death, particularly after cardioembolic TIA/stroke. Further validation is required, in particular, in studies using more extensive cardiac evaluation.

Biomarkers and mortality after transient ischemic attack and minor ischemic stroke: population-based study.

BACKGROUND AND PURPOSE: Premature death after transient ischemic attack or stroke is more often because of heart disease or cancer than stroke. Previous studies found blood biomarkers not usefully predictive of nonfatal stroke but possibly of all-cause death. This association might be explained by potentially treatable occult cardiac disease or cancer. We therefore aimed to validate the association of a panel of biomarkers with all-cause death, particularly cardiac death and cancer death, despite the absence of associations with risk of nonfatal vascular events. METHODS: Fifteen biomarkers were measured in 929 consecutive patients in a population-based study (Oxford Vascular Study), recruited from 2002 and followed up to 2013. Associations were determined by Cox regression. Model discrimination was assessed by c-statistic and the integrated discrimination improvement. RESULTS: During 5560 patient-years of follow-up, none of the biomarkers predicted risk of nonfatal vascular events. However, soluble tumor necrosis factor α receptor-1, von Willebrand factor, heart-type fatty-acid-binding protein, and N-terminal pro-B-type natriuretic peptide were independently predictive of all-cause death (n=361; adjusted hazard ratio per SD, 95% confidence interval: heart-type fatty-acid-binding protein: 1.31, 1.12-1.56, P=0.002; N-terminal pro-B-type natriuretic peptide: 1.34, 1.11-1.62, P=0.002; soluble tumor necrosis factor α receptor-1: 1.45, 1.26-1.66, P=0.02; von Willebrand factor: 1.19, 1.04-1.36, P=0.01). The independent contribution of the four biomarkers taken together added prognostic information and improved model discrimination (integrated discrimination improvement=0.028, P=0.0001). N-terminal pro-B-type natriuretic peptide was most predictive of vascular death (adjusted hazard ratio=1.80, 95% confidence interval, 1.34-2.41, P<0.0001), whereas heart-type fatty-acid-binding protein predicted cancer deaths (1.64, 1.26-2.12, P=0.0002). Associations were strongest in patients without known prior cardiac disease or cancer. CONCLUSIONS: Several biomarkers predicted death of any cause after transient ischemic attack and minor stroke. N-terminal pro-B-type natriuretic peptide and heart-type fatty-acid-binding protein might improve patient selection for additional screening for occult cardiac disease or cancer, respectively. However, our results require validation in future studies.

Population-based study of blood biomarkers in prediction of subacute recurrent stroke.

BACKGROUND AND PURPOSE: Risk of recurrent stroke is high in the first few weeks after transient ischemic attack or stroke and clinical risk prediction tools have only limited accuracy, particularly after the hyperacute phase. Previous studies of the predictive value of biomarkers have been small, been done in selected populations, and have not concentrated on the acute phase or on intensively treated populations. We aimed to determine the predictive value of a panel of blood biomarkers in intensively treated patients early after transient ischemic attack and stroke. METHODS: We studied 14 blood biomarkers related to inflammation, thrombosis, atherogenesis, and cardiac or neuronal cell damage in early transient ischemic attack or ischemic stroke in a population-based study (Oxford Vascular Study). Biomarker levels were related to 90-day risk of recurrent stroke as hazard ratio (95% confidence interval) per decile increase, adjusted for age and sex. RESULTS: Among 1292 eligible patients, there were 53 recurrent ischemic strokes within 90 days. There were moderate correlations (r=0.40-0.61; P<0.0001) between the inflammatory biomarkers and between the cell damage and thrombotic subsets. Associations with risk of early recurrent stroke were weak, with significant associations limited to interleukin-6 (adjusted hazard ratio, 1.12; 1.01-1.24; P=0.033) and C-reactive protein (adjusted hazard ratio, 1.15; 1.02-1.30; P=0.022) after adjusting for age, sex, hypertension, smoking, and diabetes mellitus although P-selectin seemed to predict stroke after transient ischemic attack (adjusted hazard ratio, 1.28; 1.00-1.63; P=0.046). CONCLUSIONS: In the largest study to date, we found limited predictive use for early recurrent stroke for a panel of inflammatory, thrombotic, and cell damage biomarkers.

DNA-mediated signaling by proteins with 4Fe-4S clusters is necessary for genomic integrity.

Iron-sulfur clusters have increasingly been found to be associated with enzymes involved in DNA processing. Here we describe a role for these redox clusters in DNA-mediated charge-transport signaling in E. coli between DNA repair proteins from distinct pathways. DNA-modified electrochemistry shows that the 4Fe-4S cluster of DNA-bound DinG, an ATP-dependent helicase that repairs R-loops, is redox-active at cellular potentials and ATP hydrolysis increases DNA-mediated redox signaling. Atomic force microscopy experiments demonstrate that DinG and Endonuclease III (EndoIII), a base excision repair enzyme, cooperate at long-range using DNA charge transport to redistribute to regions of DNA damage. Genetics experiments, moreover, reveal that this DNA-mediated signaling among proteins also occurs within the cell and, remarkably, is required for cellular viability under conditions of stress. Silencing the gene encoding EndoIII in a strain of E. coli where repair by DinG is essential results in a significant growth defect that is rescued by complementation with EndoIII but not with an EndoIII mutant that is enzymatically active but unable to carry out DNA charge transport. This work thus elucidates a fundamental mechanism to coordinate the activities of DNA repair enzymes across the genome.

17q25 Locus is associated with white matter hyperintensity volume in ischemic stroke, but not with lacunar stroke status.

BACKGROUND AND PURPOSE: Recently, a novel locus at 17q25 was associated with white matter hyperintensities (WMH) on MRI in stroke-free individuals. We aimed to replicate the association with WMH volume (WMHV) in patients with ischemic stroke. If the association acts by promoting a small vessel arteriopathy, it might be expected to also associate with lacunar stroke. METHODS: We quantified WMH on MRI in the stroke-free hemisphere of 2588 ischemic stroke cases. Association between WMHV and 6 single-nucleotide polymorphisms at chromosome 17q25 was assessed by linear regression. These single-nucleotide polymorphisms were also investigated for association with lacunar stroke in 1854 cases and 51 939 stroke-free controls from METASTROKE. Meta-analyses with previous reports and a genetic risk score approach were applied to identify other novel WMHV risk variants and uncover shared genetic contributions to WMHV in community participants without stroke and ischemic stroke. RESULTS: Single-nucleotide polymorphisms at 17q25 were associated with WMHV in ischemic stroke, the most significant being rs9894383 (P=0.0006). In contrast, there was no association between any single-nucleotide polymorphism and lacunar stroke. A genetic risk score analysis revealed further genetic components to WMHV shared between community participants without stroke and ischemic stroke. CONCLUSIONS: This study provides support for an association between the 17q25 locus and WMH. In contrast, it is not associated with lacunar stroke, suggesting that the association does not act by promoting small-vessel arteriopathy or the same arteriopathy responsible for lacunar infarction.

Patterns of Sexualized Drug Use among Gay, Bisexual, and Other Men Who Have Sex with Men Living with HIV: Insights from a Comprehensive Study-The U-SEX-2 GESIDA 9416 Study.

BACKGROUND: Sexualized drug use (SDU) has become a public health concern in recent years. This study aimed to estimate the prevalence of SDU in gay, bisexual, and other men who have sex with men living with HIV (HIV + GBMSM) in Madrid during 2019/2020 and compare it with data from 2016/2017 in order to detect changes in patterns. METHODS: We analyzed the frequency of SDU in a sample of HIV + GBMSM attending HIV clinics, who participated in an anonymous online survey regarding sexual behavior and recreational drug use. The association between SDU, sexual risk behaviors, and STIs was evaluated. RESULTS: This study included 424 HIV + GBMSM, with a mean age of 40 (10.43) years. Overall, 94% (396) reported being sexually active. Additionally, 33% (140) had been diagnosed with an STI within the previous year. Moreover, 54% (229) had used drugs in the last year, 25% (107) engaged in SDU, and 16% (17) reported engagement in slamsex. After adjusting for confounding factors, SDU was associated with STIs, fisting, unprotected anal intercourse, and having >24 sexual partners in the last year. According to the DUDIT test scores, 80% (81) probably had problematic drug use (≥6 points), and 8% (8) probable drug dependence (≥25 points). When comparing the U-SEX-1 (2016/2017) data with the U-SEX-2 (2019/2020) data, no significant differences were found in the proportion of participants practicing SDU or slamming. CONCLUSIONS: The prevalence of SDU among HIV + GBMSM has remained high in recent years and without significant changes. The risk of problematic drug use among those who practice SDU is high. We observed a clear association between SDU, high-risk sexual behaviors, and STIs.

Development of ß-globin gene correction in human hematopoietic stem cells as a potential durable treatment for sickle cell disease.

Sickle cell disease (SCD) is the most common serious monogenic disease with 300,000 births annually worldwide. SCD is an autosomal recessive disease resulting from a single point mutation in codon six of the ß-globin gene (HBB). Ex vivo ß-globin gene correction in autologous patient-derived hematopoietic stem and progenitor cells (HSPCs) may potentially provide a curative treatment for SCD. We previously developed a CRISPR-Cas9 gene targeting strategy that uses high-fidelity Cas9 precomplexed with chemically modified guide RNAs to induce recombinant adeno-associated virus serotype 6 (rAAV6)-mediated HBB gene correction of the SCD-causing mutation in HSPCs. Here, we demonstrate the preclinical feasibility, efficacy, and toxicology of HBB gene correction in plerixafor-mobilized CD34+ cells from healthy and SCD patient donors (gcHBB-SCD). We achieved up to 60% HBB allelic correction in clinical-scale gcHBB-SCD manufacturing. After transplant into immunodeficient NSG mice, 20% gene correction was achieved with multilineage engraftment. The long-term safety, tumorigenicity, and toxicology study demonstrated no evidence of abnormal hematopoiesis, genotoxicity, or tumorigenicity from the engrafted gcHBB-SCD drug product. Together, these preclinical data support the safety, efficacy, and reproducibility of this gene correction strategy for initiation of a phase 1/2 clinical trial in patients with SCD.

New Psychoactive Drugs.

Carta al editor.

Lack of association between aspirin responsiveness and seven candidate gene haplotypes in patients with symptomatic vascular disease.

We studied the effect of prophylactic aspirin (ASA) ingestion on platelet function in 463 patients with stroke, transient ischemic attack (TIA) or acute coronary disease (ACD), using the Platelet Function Analyzer-100 (PFA-100). We correlated ASA responsiveness with haplotypes of seven candidate genes, selected for their documented role in platelet function, namely, the genes for integrins alpha2beta1and alphaIIbbeta3 (ITGA2, ITGA2B, and ITGB3), platelet glycoproteins Ibalpha and VI (GPIBA and GP6), the purinergic receptor P2Y1 (P2RY1), and prostaglandin H synthase 1 (PTGS1 = COX1). Non-responsiveness to ASA was defined as the failure of prior ASA ingestion to prolong the PFA-100 closure time (CT) when blood was perfused through cartridges coated with collagen plus epinephrine (CEPI-CT). ASA non-responsiveness was observed in 114 of 463 patients (24.6 %), but was not associated with haplotypes of any of the seven candidate genes. There was also no association between any haplotypes and the CT when blood was perfused through cartridges coated with collagen plus ADP (CADP-CT). The ASA non-responsive cohort had significantly increased whole blood platelet counts (p = 0.03) and plasma von Willebrand Factor antigen levels (p < 0.001), which likely contributes to resistance to the inhibitory effects of ASA in the PFA-100.

Drug-related and psychopathological symptoms in HIV-positive men who have sex with men who inject drugs during sex (slamsex): Data from the U-SEX GESIDA 9416 Study.

OBJECTIVES: Sexualized intravenous drug use, also known as slamsex, seems to be increasing among HIV-positive men who have sex with men (MSM). Physical and psychopathological symptoms have previously been reported in this population, although research on the subject of slamsex is scarce. The objectives of our study were to describe the psychopathological background of a sample of HIV-positive MSM who engaged in slamsex during the previous year and to compare physical, psychopathological, and drug-related symptoms between these participants and those who engaged in non-injecting sexualized drug use. DESIGN AND METHODS: Participants (HIV-positive MSM) were recruited from the U-Sex study in 22 HIV clinics in Madrid during 2016-17. All participants completed an anonymous cross-sectional online survey on sexual behavior and recreational drug use. When participants met the inclusion criteria, physicians offered them the opportunity to participate and gave them a card with a unique code and a link to access the online survey. The present analysis is based on HIV-positive MSM who had engaged in slamsex and non-injecting sexualized drug use. RESULTS: The survey sample comprised 742 participants. Of all the participants who completed the survey, 216 (29.1%) had engaged in chemsex, and of these, 34 (15.7%) had engaged in slamsex. Participants who engaged in slamsex were more likely to have current psychopathology (depression, anxiety, and drug-related disorders) than participants who engaged in non-injecting sexualized drug use. In addition, participants who engaged in slamsex more frequently reported high-risk sexual behaviors and polydrug use and were more often diagnosed with sexually transmitted infections (STIs) and hepatitis C than those who did not inject drugs. Compared with participants who did not inject drugs, participants who engaged in slamsex experienced more severe drug-related symptoms (withdrawal and dependence), symptoms of severe intoxication (loss of consciousness), and severe psychopathological symptoms during or after slamsex (eg, paranoid thoughts and suicidal behaviors). CONCLUSION: Slamsex is closely associated with current psychiatric disorders and severe drug-related and psychiatric symptoms.

Lack of reproducibility of assessment of aspirin responsiveness by optical aggregometry and two platelet function tests.

The term aspirin-resistance describes the failure of aspirin to inhibit thromboxane A(2) production. Many new tests have become available for potentially measuring aspirin responses but some are non-specific and do not isolate COX-1 activity. We previously demonstrated that agreement between two tests (PFA-100 and VerifyNow-ASA) and light transmission aggregation (LTA) was no greater than would be expected by chance. In this study we re-tested the same patients using identical methods after 1 year to determine whether poor agreement might have been due to assessment in the acute phase and whether the results of the individual tests are consistent over time. Platelet function by all three tests was re-tested in the 72 patients who were alive and still receiving low dose ASA therapy one year after the first tests were performed. On re-testing the prevalence of ASA non-responsiveness compared with baseline was 10% vs 17% by the VerifyNow-ASA test, 25% vs 22% by the PFA-100(R), and 1% vs 5% by LTA. Agreement between the tests at 1 year remained poor (kappas: 0.02-0.17) and only one patient was identified as a non-responder by all three tests, in keeping with the theoretical differences between the tests. Within test comparisons of baseline vs 1 year showed moderate agreement for the PFA-100(R) (kappa = 0.44, 95% CI 0.19-0.68, p = 0.0006), a fair agreement for VerifyNow-ASA (kappa = 0.34, 0.04-0.64, p = 0.12) and poor agreement for LTA (kappa = 0.14, -0.11 -0.39, p = 0.24 for ADP; kappa = 0.09, -0.21-0.39, p = 0.41 for arachidonic acid). Agreement between the three tests in identifying aspirin non-responsiveness remained poor in patients who had been taking aspirin for at least 1 year follow-up. Reproducibility over time was no greater than chance for LTA and only moderate for VerifyNow-ASA and PFA-100(R). Lack of consistency over time in identification of apparently non-responsiveness individuals is likely to substantially undermine any ability of these tests to predict risk of recurrent vascular events.

Sexualized Drug Use (Chemsex) Is Associated with High-Risk Sexual Behaviors and Sexually Transmitted Infections in HIV-Positive Men Who Have Sex with Men: Data from the U-SEX GESIDA 9416 Study.

The magnitude of sexualized drug use (SDU), also known as chemsex, and its association with sexually transmitted infections (STI) has not been systematically explored in HIV-positive patients. This study aimed to calculate the prevalence of SDU and associated factors in a sample of HIV-positive men who have sex with men (MSM) in Spain. We calculated the frequency of SDU in a sample of HIV-positive MSM who responded to an anonymous online survey on sexual behavior and recreational drug use. We also analyzed differences between those who responded and those who did not (data taken from the physician's registry). The association between SDU, sexual risk behaviors, and STI was evaluated using a univariate and a multivariate analysis. Data were collected and managed using Research Electronic Data Capture (REDCap). The survey was completed by 742 HIV-positive MSM, of whom 60% had had unprotected anal intercourse (UAI), 62% had been diagnosed with a STI, and 216 (29.1%) reported recent SDU (slamsex in 16% of cases). In the multivariate analysis, patients who engaged in SDU were more likely to have had high-risk sexual behaviors and a diagnosis of STI than participants who did not engage in SDU. A diagnosis of hepatitis C was independently associated with slamsex (5.2 [95% confidence interval (CI), 2.06-13.13]; p < 0.001), chemsex (2.51 [95% CI, 1.28-4.91]; p = 0.007), and UAI (1.82 [95% CI, 0.90-3.70]; p = 0.094). The magnitude of SDU or chemsex in our sample is relatively high. We found a clear association between SDU, high-risk sexual behaviors, and STI including hepatitis C.

Association between obsessive-compulsive disorder and a variable number of tandem repeats polymorphism in intron 2 of the serotonin transporter gene.

BACKGROUND: Pharmacological studies indicate a dysregulation of the serotonergic system in obsessive-compulsive disorder (OCD). A variable number tandem repeats (VNTR) polymorphism with three alleles (Stin2.9, Stin2.10, Stin2.12) has been described in intron 2 of the serotonin transporter (5-HTT) gene. This polymorphism has been associated with unipolar depression, bipolar disorder, schizophrenia, and anxiety disorders including OCD. METHODS: The association between OCD and the polymorphism is examined in 97 OCD patients, 578 psychiatric controls and 406 healthy controls, all Spanish Caucasians. RESULTS: Genotype frequencies for the polymorphism were significantly different in OCD patients, psychiatric patients and controls. There was a significant excess of 12/12 and 12/10 genotypes in OCD patients compared to psychiatric patients and controls. CONCLUSIONS: Our results indicate a possible association between the Stin2.12 allele of the VNTR polymorphism and OCD.

Platelet monoamine oxidase activity in obsessive-compulsive disorder.

Response to SSRIs suggests the implication of the serotonergic system in obsessive-compulsive disorder (OCD). However, biological studies on serotonergic function in OCD have yielded contradictory results. Platelet monoamine oxidase (MAO) activity has been proposed as an index of cerebral serotonin activity. The aim of this study was to examine platelet MAO activity in 29 OCD patients and 29 healthy controls matched by age, sex and tobacco use. We also explored the relationship between platelet MAO activity and aggressive obsessions in OCD patients. There were no differences in platelet MAO activity between OCD patients and healthy controls. We found a significant correlation between platelet MAO activity and Y-BOCS scores in the group of patients with Y-BOCS scores >15. OCD patients with aggressive obsessions had significantly lower levels of platelet MAO activity than patients without aggressive obsessions. Our results suggest that platelet MAO activity may be a marker of OCD severity, and that low platelet MAO activity may be associated with aggressive obsessions in OCD patients.

Electrochemical and structural characterization of Azotobacter vinelandii flavodoxin II.

Azotobacter vinelandii flavodoxin II serves as a physiological reductant of nitrogenase, the enzyme system mediating biological nitrogen fixation. Wildtype A. vinelandii flavodoxin II was electrochemically and crystallographically characterized to better understand the molecular basis for this functional role. The redox properties were monitored on surfactant-modified basal plane graphite electrodes, with two distinct redox couples measured by cyclic voltammetry corresponding to reduction potentials of -483 ± 1 mV and -187 ± 9 mV (vs. NHE) in 50 mM potassium phosphate, 150 mM NaCl, pH 7.5. These redox potentials were assigned as the semiquinone/hydroquinone couple and the quinone/semiquinone couple, respectively. This study constitutes one of the first applications of surfactant-modified basal plane graphite electrodes to characterize the redox properties of a flavodoxin, thus providing a novel electrochemical method to study this class of protein. The X-ray crystal structure of the flavodoxin purified from A. vinelandii was solved at 1.17 Å resolution. With this structure, the native nitrogenase electron transfer proteins have all been structurally characterized. Docking studies indicate that a common binding site surrounding the Fe-protein [4Fe:4S] cluster mediates complex formation with the redox partners Mo-Fe protein, ferredoxin I, and flavodoxin II. This model supports a mechanistic hypothesis that electron transfer reactions between the Fe-protein and its redox partners are mutually exclusive.