The Assembly Factor Pet117 Couples Heme a Synthase Activity to Cytochrome Oxidase Assembly.

Heme a is an essential metalloporphyrin cofactor of the mitochondrial respiratory enzyme cytochrome c oxidase (CcO). Its synthesis from heme b requires several enzymes, including the evolutionarily conserved heme a synthase (Cox15). Oligomerization of Cox15 appears to be important for the process of heme a biosynthesis and transfer to maturing CcO. However, the details of this process remain elusive, and the roles of any additional CcO assembly factors that may be involved remain unclear. Here we report the systematic analysis of one such uncharacterized assembly factor, Pet117, and demonstrate in Saccharomyces cerevisiae that this evolutionarily conserved protein is necessary for Cox15 oligomerization and function. Pet117 is shown to reside in the mitochondrial matrix, where it is associated with the inner membrane. Pet117 functions at the later maturation stages of the core CcO subunit Cox1 that precede Cox1 hemylation. Pet117 also physically interacts with Cox15 and specifically mediates the stability of Cox15 oligomeric complexes. This Cox15-Pet117 interaction observed by co-immunoprecipitation persists in the absence of heme a synthase activity, is dependent upon Cox1 synthesis and early maturation steps, and is further dependent upon the presence of the matrix-exposed, unstructured linker region of Cox15 needed for Cox15 oligomerization, suggesting that this region mediates the interaction or that the interaction is lost when Cox15 is unable to oligomerize. Based on these findings, it was concluded that Pet117 mediates coupling of heme a synthesis to the CcO assembly process in eukaryotes.

Analysis of Oligomerization Properties of Heme a Synthase Provides Insights into Its Function in Eukaryotes.

Heme a is an essential cofactor for function of cytochrome c oxidase in the mitochondrial electron transport chain. Several evolutionarily conserved enzymes have been implicated in the biosynthesis of heme a, including the heme a synthase Cox15. However, the structure of Cox15 is unknown, its enzymatic mechanism and the role of active site residues remain debated, and recent discoveries suggest additional chaperone-like roles for this enzyme. Here, we investigated Cox15 in the model eukaryote Saccharomyces cerevisiae via several approaches to examine its oligomeric states and determine the effects of active site and human pathogenic mutations. Our results indicate that Cox15 exhibits homotypic interactions, forming highly stable complexes dependent upon hydrophobic interactions. This multimerization is evolutionarily conserved and independent of heme levels and heme a synthase catalytic activity. Four conserved histidine residues are demonstrated to be critical for eukaryotic heme a synthase activity and cannot be substituted with other heme-ligating amino acids. The 20-residue linker region connecting the two conserved domains of Cox15 is also important; removal of this linker impairs both Cox15 multimerization and enzymatic activity. Mutations of COX15 causing single amino acid conversions associated with fatal infantile hypertrophic cardiomyopathy and the neurological disorder Leigh syndrome result in impaired stability (S344P) or catalytic function (R217W), and the latter mutation affects oligomeric properties of the enzyme. Structural modeling of Cox15 suggests these two mutations affect protein folding and heme binding, respectively. We conclude that Cox15 multimerization is important for heme a biosynthesis and/or transfer to maturing cytochrome c oxidase.

An exploratory study of the influence of clinico-demographic variables on swallowing and swallowing-related quality of life in a cohort of oral and oropharyngeal cancer patients treated with primary surgery.

There are insufficient data on swallowing and the consequences of its dysfunction in patients with cancers of the oral cavity (OC) and oropharynx (OP) that are treated with primary surgery. The study attempts to explore the effect of important clinico-demographic variables on post-treatment swallowing and related quality of life (QOL) in post-surgical OC and OP cancer patients. Sixty-two consecutive OC and OP cancer patients completed the MD Anderson Dysphagia Inventory (MDADI) questionnaire. Mean scores were computed. Comparison of scores based on mean ranks were performed using Mann-Whitney U test or Kruskal-Wallis test. Level of significance was set at P ≤ 0.02. Adjustments were made for multiple comparisons. Significantly worse mean (SD) QOL scores were observed in late T-stage (T3/T4) versus early T-stage (T1/T2) patients for global domain, physical domain, functional domain and emotional domains [44.4 (21.9) vs. 78.7 (22.7) (P < 0.001); 50.0 (9.4) vs. 75.9 (16.3), (P < 0.0001); 57.8 (20.6) vs. 84.1 (16.7), (P < 0.001) and 55.2 (18.0) vs. 78.5 (16.3), (P < 0.001)], respectively. Patients undergoing reconstruction versus without reconstruction had worse QOL scores; 58.8 (26.9) versus 79.5 (22.8), (P < 0.01); 61.2 (15.1) versus 76.4 (17.5), (P = 0.002); 65.4 (20.5) versus 86.3 (15.9), (P < 0.0001) and 63.3 (18.8) versus 79.8 (16.3), (P < 0.01), respectively, for global, physical, functional and emotional domains. Advanced T-stage, reconstruction, younger age and base of tongue tumours have a negative impact on post-treatment swallow function and related QOL in these patients.

Extrusion of metal radiological marker from a total ankle replacement insert: a case report.

Total ankle arthroplasty has become an increasingly performed procedure for the treatment of ankle arthritis. Failures related to polyethylene inserts can result from uncorrected deformities or malalignment of the components. We report a case of a 63-year-old man who underwent total ankle arthroplasty for osteoarthritis of the ankle. The talar component was placed in neutral alignment. Initial postoperative recovery and rehabilitation were unremarkable. At 9 months postoperatively, plain radiographs of the ankle showed worsening varus tilt when compared with radiographs taken earlier. There was also radiographic evidence of separation of the posterior metal marker, suggestive of a fracture of the polyethylene insert. Revision surgery to correct the varus tilt and replace the polyethylene insert was performed. At operation, the polyethylene insert was found to be intact with no evidence of fracture. The posterior metal marker of the polyethylene insert was found to be extruded from the insert. Small degrees of ankle prosthesis malalignment can lead to various degrees of polyethylene liner failure, such as metal marker extrusion. This article also shows that these metal markers may not be accurate indicators of the integrity of the polyethylene insert.

Bone anchors or interference screws? A biomechanical evaluation for autograft ankle stabilization.

BACKGROUND: Autograft stabilization uses free semitendinosus tendon grafts to anatomically reconstruct the anterior talofibular ligament. Study aims were to evaluate the biomechanical properties of Mitek GII anchors compared with the Arthrex Bio-Tenodesis Screw for free tendon reconstruction of the anterior talofibular ligament. NULL HYPOTHESIS: There are no differences in load to failure and percentage specimen elongation at failure between the 2 methods. STUDY DESIGN: Controlled laboratory study using porcine models. METHODS: Sixty porcine tendon constructs were failure tested. Re-creating the pull of the anterior talofibular ligament, loads were applied at 70 degrees to the bones. Thirty-six tendons were fixed to porcine tali and tested using a single pull to failure; 10 were secured with anchors and No. 2 Ethibond, 10 with anchors and FiberWire, 10 with screws and Fiberwire, and 6 with partially gripped screws. Cyclic preloading was conducted on 6 tendons fixed by anchors and on 6 tendons fixed by screws before failure testing. Two groups of 6 components fixed to the fibula were also tested. RESULTS: The talus single-pull anchor group produced a mean load of 114 N and elongation of 37% at failure. The talus single-pull screw group produced a mean load of 227 N and elongation of 22% at failure (P <.05). Cyclic preloading at 65% failure load before failure testing produced increases in load and decreases in elongation at failure. Partially gripped screws produced a load of 133 N and elongation of 30% at failure. The fibula model produced significant increases in load to failure for both. The human anterior talofibular ligament has loads of 139 N at failure with instability occurring at 20% elongation. CONCLUSIONS: Interference screw fixation produced significantly greater failure strength and less elongation at failure than bone anchors. CLINICAL RELEVANCE: The improved biomechanics of interference screws suggests that these may be more suited to in vivo reconstruction of the anterior talofibular ligament than are bone anchors.

Preclinical evaluation of the anticancer activity and toxicity of 9-nitro-20(S)-camptothecin (Rubitecan).

The purpose of this study is to establish the maximum tolerated dose of rubitecan in mice, dogs and men and to establish the anticancer activity of such dose against human tumors xenografted in nude mice. Nude mice received increasing doses of Rubitecan by intrastomach injection until the maximum tolerated dose (MTD) had been established for both the single dose and the multiple doses at the schedule of 5 days on, 2 days off. Extrapolating from the mouse data, MTD was determined for oral administration in dogs and man. Levels of the drug in plasma were determined by high pressure liquid chromatography (HPLC). Using maximum tolerated multiple doses, the sensitivity of human cancer xenografts in nude mice to Rubitecan was determined. MTD of Rubitecan in mice for multiple doses intrastomach at the schedule of 5+,2- was 1 mg/kg/day. MTD in dogs was also 1 mg/kg/day, administered orally but at the schedule of 4+,3-. In man, it was 1 mg/m2/day at the schedule of 5+,2-. Treatment of human cancer xenografts in nude mice with MTD of Rubitecan resulted in 100% growth inhibition of 30/30 tumors tested and in 24/30 in their total disappearance. These 30 tumors comprised all the most common human cancers: lung, colorectal, breast, pancreatic, ovarian, prostate, stomach, melanoma and a leukemia. From the data collected, it appears that rubitecan is a very promising anticancer drug with high potency against a wide spectrum of human cancers. These cancers growing as xenografts in nude mice are always growth inhibited (30/30) and frequently (24/30) totally destroyed by the administration of non-toxic doses of Rubitecan.