Assignment of the 600-MHz 1H-NMR spectrum of amicyanin from Thiobacillus versutus by two-dimensional NMR methods provides information on secondary structure

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Abstract
The nearly complete assignment (pH 6.8; T 310 K) of the 1H-NMR spectrum of reduced amicyanin from Thiobacillus versutus is reported. Experimental evidence is presented, that the structure of the amicyanin contains two beta-sheets, a feature common to plastocyanins and azurins. The loops joining the beta-strands have also been identified. The loop F-G (Thr94-Phe98), together with the flanking residues Cys93 and Met99, comprises three of the four copper ligands and is short compared to similar loops in plastocyanin and azurin. His96 turns out to be the copper ligand that can be protonated. Amicyanin resembles plastocyanin in overall structure but differs from it on account of an N-terminal strand of 22 amino acids in front of strand A, shorter loops A-B, D-E and F-G and the absence of any alpha-helical segments.