Conformational properties of cardiolipin-bound cytochrome c.

Interactions of cytochrome c (cyt c) with cardiolipin (CL) are important for both electron transfer and apoptotic functions of this protein. A sluggish peroxidase in its native state, when bound to CL, cyt c catalyzes CL peroxidation, which contributes to the protein apoptotic release. The heterogeneous CL-bound cyt c ensemble is difficult to characterize with traditional structural methods and ensemble-averaged probes. We have employed time-resolved FRET measurements to evaluate structural properties of the CL-bound protein in four dansyl (Dns)-labeled variants of horse heart cyt c. The Dns decay curves and extracted Dns-to-heme distance distributions P(r) reveal a conformational diversity of the CL-bound cyt c ensemble with distinct populations of the polypeptide structures that vary in their degree of protein unfolding. A fraction of the ensemble is substantially unfolded, with Dns-to-heme distances resembling those in the guanidine hydrochloride-denatured state. These largely open cyt c structures likely dominate the peroxidase activity of the CL-bound cyt c ensemble. Site variations in P(r) distributions uncover structural features of the CL-bound cyt c, rationalize previous findings, and implicate the prime role of electrostatic interactions, particularly with the protein C terminus, in the CL-induced unfolding.

Multifaceted effects of ATP on cardiolipin-bound cytochrome c.

Using a collection of dye-labeled cytochrome c (cyt c) variants, we identify transformations of the heterogeneous cardiolipin (CL)-bound cyt c ensemble with added ATP. Distributions of dye-to-heme distances P(r) from time-resolved fluorescence resonance energy transfer show that ATP decreases the population of largely unfolded cyt c conformers, but its effects are distinct from those of a simple salt. The high peroxidase activity of CL-bound cyt c with added ATP suggests binding interactions that favor protein structures with the open heme pocket. Although ATP weakens cyt c-CL binding interactions, it also boosts the apoptosis-relevant peroxidase activity of CL-bound cyt c.

Medical therapy for atherosclerotic cardiovascular disease in patients with myocardial injury after non-cardiac surgery.

BACKGROUND: Myocardial injury after non-cardiac surgery (MINS) is a common post-operative cardiovascular complication and is associated with short and long-term mortality. The objective of this study was to describe the contemporary management of patients with and without MINS after total joint and spine orthopedic surgery at a large urban health system in the United States. METHODS: Adults admitted for total joint and major spine surgery from January 2013 through December 2015 with ≥1 cardiac troponin (cTn) measurement during their hospitalization were identified. MINS was defined by a peak cTn above the 99th percentile of the upper reference limit. Demographics, medical comorbidities, and admission and discharge medications were reviewed for all patients. RESULTS: A total of 2561 patients underwent 2798 orthopedic surgeries, and 236 cases of MINS were identified. Patients with MINS were older (71.9 ±â€¯10.9 vs. 67.0 ±â€¯10.0, p < 0.001) and more likely to have cardiovascular risk factors, including hypertension, chronic kidney disease, prior stroke, coronary artery disease, prior MI, and a history of heart failure. Among patients with MINS, only 112 (47.5%) were discharged on a combination of aspirin and statin. Patients with MINS were more likely to be prescribed a statin (154 [65.3%] vs. 1463 [57.1%], p = 0.018), beta-blocker (147 [62.3%] vs. 1194 [46.6%], p < 0.001), and oral anticoagulation (65 [27.5%] vs. 436 [17.0%], p < 0.001) than patients without MINS. CONCLUSIONS: The proportion of patients with MINS who were prescribed medical therapy for atherosclerotic cardiovascular disease was low. Additional efforts to determine optimal management of MINS are warranted.

Becoming a peroxidase: cardiolipin-induced unfolding of cytochrome c.

Interactions of cytochrome c (cyt c) with a unique mitochondrial glycerophospholipid cardiolipin (CL) are relevant for the protein's function in oxidative phosphorylation and apoptosis. Binding to CL-containing membranes promotes cyt c unfolding and dramatically enhances the protein's peroxidase activity, which is critical in early stages of apoptosis. We have employed a collection of seven dansyl variants of horse heart cyt c to probe the sequence of steps in this functional transformation. Kinetic measurements have unraveled four distinct processes during CL-induced cyt c unfolding: rapid protein binding to CL liposomes; rearrangements of protein substructures with small unfolding energies; partial insertion of the protein into the lipid bilayer; and extensive protein restructuring leading to "open" extended structures. While early rearrangements depend on a hierarchy of foldons in the native structure, the later process of large-scale unfolding is influenced by protein interactions with the membrane surface. The opening of the cyt c structure exposes the heme group, which enhances the protein's peroxidase activity and also frees the C-terminal helix to aid in the translocation of the protein through CL membranes.