title: Approaching the speed limit for Greek Key beta-barrel formation: transition-state movement tunes folding rate of zinc-substituted azurin.
abstract: Azurin is a blue-copper protein with a beta-barrel structure of Greek Key topology. In vitro, copper can be substituted with zinc without change in protein structure. We here analyze the kinetic folding behavior of zinc-substituted Pseudomonas aeruginosa azurin. Our findings can be summarized in three key conclusions: first, zinc remains strongly bound to the polypeptide upon unfolding, suggesting that the cofactor may bind to the protein before polypeptide folding in vivo. Second, the semi-logarithmic plot of folding and unfolding rates for zinc-substituted azurin as a function of denaturant concentration exhibits curvature due to a changing transition-state structure. Third, the extrapolated folding speed in water for zinc-substituted azurin is similar to that of other proteins with the same topology, implying that there is a speed limit that can be modulated by stability-driven transition-state movement for formation of beta-barrel structures with Greek Key topology.
mesh_terms: D001400:Azurin / Q000737:chemistry* / Q000378:metabolism; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000737:chemistry; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*
chemical_list: D001400:Azurin; D015032:Zinc