The Impact of Second Coordination Sphere Methionine-Aromatic Interactions in Copper Proteins.

The interplay between the primary and secondary coordination spheres in biological metal sites plays an essential role in controlling their properties. Some of the clearest examples of this are from copper sites in blue and purple copper proteins. Many such proteins contain methionine (Met) in the primary coordination sphere as a weakly bound ligand to Cu. While the effects of replacing the coordinated Met are understood, less so is the importance of its second-sphere interactions. In this combined informatics and experimental study, we first present a bioinformatics investigation of the second-sphere environments in biological Met-Cu motifs. The most common interaction is between the Met-CH3 and the π-face of a phenylalanine (Phe) (81% of surveyed structures), tyrosine (Tyr) (11%), and tryptophan (Trp) (8%). In most cases, the Met-CH3 also forms a contact with a π-face of one of a Cu-ligating histidine-imidazole. Such interactions are widely distributed in different Cu proteins. Second, to explore the impact of the second-sphere interactions of Met, a series of artificial Pseudomonas aeruginosa azurin proteins were produced where the native Phe15 was replaced with Tyr or Trp. The proteins were characterized using optical and magnetic resonance spectroscopies, X-ray diffraction, electrochemistry, and an investigation of the time-resolved electron-transfer kinetics of photosensitizer-modified proteins. The influence of the Cu-Met-Aro interaction on azurin's physical properties is subtle, and the hallmarks of the azurin blue copper site are maintained. In the Phe15Trp variant, the mutation to Phe15 induces changes in Cu properties that are comparable to replacement of the weak Met ligand. The broader impacts of these widely distributed interactions are discussed.

Os acromiale: evaluation and treatment.

Os acromiale is a developmental aberration in which the distal acromion fails to fuse. This aberration is often discovered incidentally but may present with a clinical picture similar to that of subacromial impingement syndrome. Treatment for symptomatic os acromiale is initially nonoperative-activity modification, physical therapy, corticosteroid injection, use of nonsteroidal anti-inflammatory medication. Nonoperative management of clinically significant, radiographically confirmed os acromiale should be pursued for at least 6 months before consideration of surgical intervention. Subacromial decompression is often necessary to address symptoms of impingement. Excision of the os fragment may provide definitive treatment for smaller fragments (<3 cm). Removal of larger fragments remains controversial and should be approached with caution. Surgical fixation of larger fragments with or without supplemental autograft in conjunction with a structured postoperative program of physical therapy can reliably provide relief for symptomatic os acromiale.