New Synthetic Routes to Iron–Sulfur Clusters: Deciphering the Repair Chemistry of [2Fe–2S] Clusters from Mononitrosyl Iron Complexes

The nitrosylation of inorganic protein cofactors, specifically that of [Fe–S] clusters to form iron nitrosyls, plays a number of important roles in biological systems. In some of these cases, it is expected that a repair process reverts the nitrosylated iron species to intact [Fe–S] clusters. The repair of nitrosylated [2Fe–2S] cluster, primarily in the form of protein-bound dinitrosyl iron complexes (DNICs), has been observed <i>in vitro</i> and <i>in vivo</i>, but the mechanism of this process remains uncertain. The present work expands upon a previous observation (Fitzpatrick et al.<i> J. Am. Chem. Soc.</i> <b>2014</b>, <i>136</i>, 7229) of the ability of mononitrosyl iron complexes (MNICs) to be converted into [2Fe–2S] clusters by the addition of nothing other than a cysteine analogue. Herein, each of the critical elementary steps in the cluster repair has been dissected to elucidate the roles of the cysteine analogue. Systematic variations of a cysteine analogue employed in the repair reaction suggest that (i) the bidentate coordination of a cysteine analogue to MNIC promotes NO release from iron, and (ii) deprotonation of the α carbon of the ferric-bound cysteine analogue leads to the C–S cleavage en route to the formation of [2Fe–2S] cluster. The [2Fe–2S] cluster bearing a cysteine analogue has also been synthesized from thiolate-bridged iron dimers of the form [Fe₂(μ-SR)₂(SR)₄]^0/2–, which implies that such species may be present as intermediates in the cluster repair. In addition to MNICs, mononuclear tetrathiolate ferric or ferrous species have been established as another form of iron from which [2Fe–2S] clusters can be generated without need for any other reagent but a cysteine analogue. The results of these experiments bring to light new chemistry of classic coordination complexes and provides further insight into the repair of NO-modified [2Fe–2S] clusters

Transformation of a Mononitrosyl Iron Complex to a [2Fe-2S] Cluster by a Cysteine Analogue

Reversible modification of iron-sulfur clusters by nitric oxide acts as a genetic switch in a group of regulatory proteins. While the conversion of [Fe-S] clusters to iron-nitrosyls has been widely studied in the past, little is known about the reverse process, the repair of [Fe-S] clusters. Reported here is a system in which a mononitrosyl iron complex (MNIC), (PPN)­[Fe­(S^<i>t</i>Bu)₃(NO)] (<b>1</b>), is converted to a [2Fe-2S] cluster, (PPN)₂[Fe₂S₂(SCH₂CH₂C­(O)­OMe)₄] (<b>2</b>). This conversion requires only the addition of a cysteine analogue, 3-mercaptomethylpropionate (MMP), at room temperature without the need for any other reagents. The identity of <b>2</b> was confirmed spectroscopically, chemically, crystallographically, and analytically. Mass spectrometry and ³⁴S labeling studies support that the bridging sulfides in <b>2</b> derive from the added MMP, the cysteine analogue. The NO lost during the conversion of <b>1</b> to <b>2</b> is trapped in a dinitrosyl iron side product, (PPN)­[Fe­(SCH₂CH₂C­(O)­OMe)₂(NO)₂] (<b>4</b>). The present system implies that MNICs are likely intermediates in the repair of NO-damaged [2Fe-2S] clusters and that cysteine is a viable molecule responsible for the destabilization of MINCs and the formation of [2Fe-2S] clusters

Results from multivariable analyses of mMRC scores, grouped as mMRC <2 and mMRC≥2, CAT, and SGRQ.

Results from multivariable analyses of mMRC scores, grouped as mMRC <2 and mMRC≥2, CAT, and SGRQ.</p

Participant selection from the I AM OLD cohort.

ObjectivesAn isolated reduction in the diffusing capacity for carbon monoxide (DLco; iso↓DLco) is one of the most common pulmonary function test (PFT) abnormalities in people living with HIV (PWH), but its clinical implications are incompletely understood. In this study, we explored whether iso↓DLco in PWH is associated with a greater respiratory symptom burden.Study designCross-sectional analysisMethodsWe used ATS/ERS compliant PFTs from PWH with normal spirometry (post-bronchodilator FEV1/FVC ≥0.7; FEV1, FVC ≥80% predicted) from the I AM OLD cohort in San Francisco, CA and Seattle, WA, grouped by DLco categorized as normal (DLco ≥lower limit of normal, LLN), mild iso↓DLco (LLN >DLco >60% predicted), and moderate-severe iso↓DLco (DLco ≤60% predicted). We performed multivariable analyses to test for associations between DLco and validated symptom-severity and quality of life questionnaires, including the modified Medical Research Council dyspnea scale (mMRC), the COPD Assessment Test (CAT), and St. George’s Respiratory Questionnaire (SGRQ), as well as between DLco and individual CAT symptoms.ResultsMild iso↓DLco was associated only with a significantly higher SGRQ score. Moderate-severe iso↓DLco was associated with significantly higher odds of mMRC ≥2 and significantly higher CAT and SGRQ scores. PWH with moderate-severe iso↓DLco had increased odds of breathlessness, decreased activity, lower confidence leaving home, and less energy.ConclusionsIso↓DLco is associated with worse respiratory symptom scores, and this association becomes stronger with worsening DLco, suggesting that impaired gas exchange alone has a significant negative impact on the quality of life in PWH. Additional studies are ongoing to understand the etiology of this finding and design appropriate interventions.</div

Participant baseline demographic and clinical characteristics (N = 189).

Participant baseline demographic and clinical characteristics (N = 189).</p

Minimal required data set.

ObjectivesAn isolated reduction in the diffusing capacity for carbon monoxide (DLco; iso↓DLco) is one of the most common pulmonary function test (PFT) abnormalities in people living with HIV (PWH), but its clinical implications are incompletely understood. In this study, we explored whether iso↓DLco in PWH is associated with a greater respiratory symptom burden.Study designCross-sectional analysisMethodsWe used ATS/ERS compliant PFTs from PWH with normal spirometry (post-bronchodilator FEV1/FVC ≥0.7; FEV1, FVC ≥80% predicted) from the I AM OLD cohort in San Francisco, CA and Seattle, WA, grouped by DLco categorized as normal (DLco ≥lower limit of normal, LLN), mild iso↓DLco (LLN >DLco >60% predicted), and moderate-severe iso↓DLco (DLco ≤60% predicted). We performed multivariable analyses to test for associations between DLco and validated symptom-severity and quality of life questionnaires, including the modified Medical Research Council dyspnea scale (mMRC), the COPD Assessment Test (CAT), and St. George’s Respiratory Questionnaire (SGRQ), as well as between DLco and individual CAT symptoms.ResultsMild iso↓DLco was associated only with a significantly higher SGRQ score. Moderate-severe iso↓DLco was associated with significantly higher odds of mMRC ≥2 and significantly higher CAT and SGRQ scores. PWH with moderate-severe iso↓DLco had increased odds of breathlessness, decreased activity, lower confidence leaving home, and less energy.ConclusionsIso↓DLco is associated with worse respiratory symptom scores, and this association becomes stronger with worsening DLco, suggesting that impaired gas exchange alone has a significant negative impact on the quality of life in PWH. Additional studies are ongoing to understand the etiology of this finding and design appropriate interventions.</div

Results from multivariable analyses of individual CAT questions.

Results from multivariable analyses of individual CAT questions.</p

Fig 3 -

a. Distribution of CAT scores by DLco category. Mantel-Haenszel test was used to test for a linear trend between CAT scores and DLco category [Ptrend Ptrend b. Distribution of SGRQ scores by DLco category. Kruskal-Wallis test was used to test for a linear trend between SGRQ scores and DLCO category [Ptrend Ptrend < 0.001 (**)].</p

Unadjusted associations of diffusing capacity for carbon monoxide and respiratory symptom scores [<i>P</i> < 0.05 (*); <i>P</i><0.01 (**); <i>P</i> < 0.001 (***)].

Unadjusted associations of diffusing capacity for carbon monoxide and respiratory symptom scores [P PP < 0.001 (***)].</p

Outcomes of multivariable analyses of predictors associated with abnormal DLco.

Outcomes of multivariable analyses of predictors associated with abnormal DLco.</p