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Title
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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.
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Authors
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H.Nar,
A.Messerschmidt,
R.Huber,
M.van de Kamp,
G.W.Canters.
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Ref.
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J Mol Biol, 1991,
221,
765-772.
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PubMed id
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Abstract
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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.
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