Role of metal in folding and stability of copper proteins in vitro

Abstract

Metal coordination is required for function of many proteins. For biosynthesis of proteins coordinating a metal, the question arises if the metal binds before, during or after folding of the polypeptide. Moreover, when the metal is bound to the protein, how does its coordination affect biophysical properties such as stability and dynamics? Understanding how metals are utilized by proteins in cells on a molecular level requires accurate descriptions of the thermodynamic and kinetic parameters involved in protein-metal complexes. Copper is one of the essential transition metals found in the active sites of many key proteins. To avoid toxicity of free copper ions, living systems have developed elaborate copper-transport systems that involve dedicated proteins that facilitate efficient and specific delivery of copper to target proteins. This review describes in vitro and in silico biophysical work assessing the role of copper in folding and stability of copper-binding proteins. Examples of proteins discussed are: a blue-copper protein (Pseudomonas aeruginosa azurin), members of copper-transport systems (bacterial CopZ, human Atox1 and ATP7B domains) and multi-copper ferroxidases (yeast Fet3p and human ceruloplasmin). The consequences of interactions between copper proteins and platinum-complexes are also discussed. This article is part of a Special Issue entitled: Cell Biology of Metals.

Identification of the Valence and Coordination Environment of the Particulate Methane Monooxygenase Copper Centers by Advanced EPR Characterization

“…It is well documented that the metalloprotein folding state can affect reduction potential. 68−70 For example, the average reduction potential for unfolded azurin is ∼130 mV higher than that of folded azurin. 68 In addition, the copper loading of azurin occurs on a millisecond time scale for unfolded protein versus a minute to hour time scale for folded protein.…”

“…68 In addition, the copper loading of azurin occurs on a millisecond time scale for unfolded protein versus a minute to hour time scale for folded protein. 70−72 In this case, Cu(I) binds favorably in the unfolded state because linear or trigonal coordination is readily accessible when the protein is unfolded. By analogy, Cu(I) might bind preferably to unfolded spmoB.…”

Cofactor Engineering for Enhancing the Flux of Metabolic Pathways

“…Likewise, increasing Fe–S levels, via overexpression of the isc (Fe–S cluster) operon, also leads to similar effects (Nakamura et al, 1999; Akhtar and Jones, 2008a). An explanation for the increased holoenzyme levels may be gleaned from studies of proteins, which utilize divalent metal ions as cofactors (Wilson et al, 2004; Bushmarina et al, 2006; Palm-Espling et al, 2012). Evidence from these published reports suggests that cofactors may aid in the folding of the polypeptide chain and, in turn, accelerate the formation of a functional protein (Goedken et al, 2000).…”

Influence of inductive effects and steric encumbrance on the catecholase activities of copper(ii) complexes of reduced Schiff base ligands

“…[1][2][3][4] Copper proteins can be further divided into three types of active sites based on their spectroscopic characteristics. 5 "Blue copper centers", also known as type-1 copper centers, are characterized by an intense CT band centered around 600 nm (ε > 2000 cm −1 M −1 ) due to Cu(II)-S cys orbital overlap, and are recognized as important electrontransfer mediators in photosynthesis and metabolism.…”