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Metal-binding loop length and not sequence dictates structure
Lookup NU author(s)
Dr Katsuko Sato
Dr Chan Li
Dr Isabelle Salard-Arnaud
Dr Mark Banfield
Professor Christopher Dennison
Sato K, Li C, Salard I, Thompson AJ, Banfield MJ, Dennison C
Proceedings of the National Academy of Sciences
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The C-terminal copper-binding loop in the beta-barrel fold of the cupredoxin azurin has been replaced with a range of sequences containing alanine, glycine, and valine residues to assess the importance of amino acid composition and the length of this region. The introduction of 2 and 4 alanines between the coordinating Cys, His, and Met results in loop structures matching those in naturally occurring proteins with the same loop lengths. A loop with 4 alanines between the Cys and His and 3 between the His and Met ligands has a structure identical to that of the WT protein, whose loop is the same length. Loop structure is dictated by length and not sequence allowing the properties of the main surface patch for interactions with partners, to which the loop is a major contributor, to be optimized. Loops with 2 amino acids between the ligands using glycine, alanine, and valine residues have been compared. An empirical relationship is found between copper site protection by the loop and reduction potential. A loop adorned with 4 methyl groups is sufficient to protect the copper ion, enabling most sequences to adequately perform this task. The mutant with 3 alanine residues between the ligands forms a strand-swapped dimer in the crystal structure, an arrangement that has not, to our knowledge, been seen previously for this family of proteins. Cupredoxins function as redox shuttles and are required to be monomeric; therefore, none have evolved with a metal-binding loop of this length.
National Academy of Sciences
Sato, Katsuko Li, Chan Salard, Isabelle Thompson, Andrew J Banfield, Mark J Dennison, Christopher BB/C504519/1/Biotechnology and Biological Sciences Research Council/United Kingdom Research Support, Non-U.S. Gov't United States Proceedings of the National Academy of Sciences of the United States of America Proc Natl Acad Sci U S A. 2009 Apr 7;106(14):5616-21. Epub 2009 Mar 19.
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