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Folding of Apominimyoglobin

Giampiero De Sanctis, Franca Ascoli and Maurizio Brunori
Proceedings of the National Academy of Sciences of the United States of America
Vol. 91, No. 24 (Nov. 22, 1994), pp. 11507-11511
Stable URL: http://www.jstor.org/stable/2366159
Page Count: 5
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Folding of Apominimyoglobin
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Abstract

The acid unfolding pathway of apominimyoglobin (apo-mini-Mb), a 108-aa fragment (aa 32-139) of horse heart apomyoglobin has been studied by means of circular dichroism, in comparison with the native apoprotein. Similar to sperm whale apomyoglobin [Hughson, F. M., Wright, P. E. \& Baldwin, R. L. (1990) Science 249, 1544-1548], a partly folded intermediate (α-helical content ≈35%) is populated at pH 4.2 for horse heart apomyoglobin. For this intermediate, Hughson et al. proposed a structural model with a compact subdomain involving tertiary interactions between the folded A, G, and H helices, with the remainder of the protein essentially unfolded. As described in this paper, a folding intermediate with an α-helical content of ≈33% is populated at pH 4.3-5.0 also in apo-mini-Mb. The acid unfolding pathway is similarly affected in both the native and the mini apoprotein by 15% trifluoroethanol, a helix-stabilizing compound. Thus, the folding of the apo-mini-Mb intermediate is similar to that observed for the native apoprotein, in spite of the absence in the miniprotein of the A helix and of a large part of the H helix, which are crucial for the stability of apo-Mb intermediate. Our results suggest that acquisition of a folded state in apo-mini-Mb occurs through an alternative pathway, which may or may not be shared also by apo-Mb.

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