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Publication Abstract from PubMed

The X-ray crystal structure of recombinant wild-type azurin from Pseudomonas aeruginosa was determined by difference Fourier techniques using phases derived from the structure of the mutant His35Leu. Two data sets were collected from a single crystal of oxidized azurin soaked in mother liquor buffered at pH 5.5 and pH 9.0, respectively. Both data sets extend to 1.93 A resolution. The two pH forms were refined independently to crystallographic R-factors of 17.6% (pH 5.5) and 17.5% (pH 9.0). The conformational transition previously attributed to the protonation/deprotonation of residue His35 (pKa(red) = 7.3, pKa(ox) = 6.2), which lies in a crevice of the protein close to the copper binding site, involves a concomitant Pro36-Gly37 main-chain peptide bond flip. At the lower pH, the protonated imidazole N delta 1 of His35 forms a strong hydrogen bond with the carbonyl oxygen from Pro36, while at alkaline pH the deprotonated N delta 1 acts as an acceptor of a weak hydrogen bond from HN Gly37. The structure of the remainder of the azurin molecule, including the copper binding site, is not significantly affected by this transition.

Crystal structure analysis of oxidized Pseudomonas aeruginosa azurin at pH 5.5 and pH 9.0. A pH-induced conformational transition involves a peptide bond flip.,Nar H, Messerschmidt A, Huber R, van de Kamp M, Canters GW J Mol Biol. 1991 Oct 5;221(3):765-72. PMID:001942029^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.