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If space is provided, bulky modification on the rim of Azurin's β‐barrel results in folded protein
Author(s) -
Pozdnyakova Irina,
Wittung-Stafshede Pernilla
Publication year - 2002
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(02)03505-6
Subject(s) - azurin , chemistry , copper protein , crystallography , cysteine , barrel (horology) , copper , stereochemistry , redox , enzyme , inorganic chemistry , biochemistry , materials science , organic chemistry , composite material
Pseudomonas aeruginosa azurin is a blue‐copper protein with a β‐barrel fold. Here we report that, at conditions where thermal unfolding of apo‐azurin is reversible , the reaction occurs in a single step with a transition midpoint ( T m ) of 69°C (pH 7). The active‐site mutation His117Gly creates a cavity in the β‐barrel near the surface but does not perturb the overall fold ( T m of 64°C, pH 7). Oxidation of the active‐site cysteine (Cysteine‐112) in wild‐type azurin, which occurs readily at higher temperatures, results in a modified protein that cannot adopt a native‐like structure. In sharp contrast, Cysteine‐112 oxidation in His117Gly azurin yields a modified apo‐azurin that appears folded and displays cooperative, reversible unfolding ( T m ∼55°C, pH 7). We conclude that azurin's β‐barrel is a rigid structural element that constrains the structure of its surface; a bulky modification can only be accommodated if complementary space is provided.