1iet
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APOCYTOCHROME B5, PH 6.2, 298 K, NMR, MINIMIZED AVERAGE STRUCTURE
OverviewOverview
In order to characterize the structural and dynamic factors that determine, the assembly in b hemoproteins, the solution structure of the 98-residue, protein apocytochrome b5 was determined by NMR methods. Over 800, experimental restraints derived from a series of two- and, three-dimensional experiments were used. Holocytochrome b5, the protein, with iron protoporphyrin-IX liganded to His-39 and His-63, contains in, sequence the following elements of secondary structure: beta 1-alpha, 1-beta 4-beta 3-alpha 2-alpha 3-beta 5-alpha 4-alpha 5-beta 2-alpha 6, [Mathews, F.S., Czerwinski, E. W., & Argos, P. (1979) The Porphyrins, Vol., 7, pp. 107-147, Academic Press, New York]. The folded holoprotein, possesses two hydrophobic cores: an extensive, functional core around the, heme (core 1), and a smaller, structural core remote from the heme (core, 2). The apoprotein was found to contain a stable four-stranded beta-sheet, encompassing beta 1, beta 2, beta 3, and beta 4 and three alpha-helices, corresponding to alpha 1, alpha 2, and alpha 6. Two short alpha-helices, (alpha 3 and alpha 5) appear to form partially, and alpha 4 is not, detected. These three helices and beta 5 border the heme binding pocket, and are disordered in the apoprotein NMR structure. According to backbone, 1H-15N NOE results, the most flexible region of the apoprotein, except for, the termini, extends from Ala-50 (in beta 5) to Glu-69 (in alpha 5). The, polypeptide segment bearing His-63 (located immediately prior to alpha 5), exhibits faster internal motions than that bearing His-39 (at the, C-terminal end of alpha 2). The latter imidazole samples a restricted, region of space, whereas the former can adopt many orientations with, respect to the stable core. It was concluded that heme removal affects the, structure and dynamics of most of core 1 whereas it leaves core 2 largely, intact. The results provide guidelines for the rational design of b, hemoproteins: a modular structure including a packed, stable core and a, partially folded binding site is anticipated to present strong kinetic and, thermodynamic advantages compared to approaches relying on the complete, formation of secondary structure prior to heme binding.
About this StructureAbout this Structure
1IET is a Single protein structure of sequence from Rattus norvegicus. Full crystallographic information is available from OCA.
ReferenceReference
Design challenges for hemoproteins: the solution structure of apocytochrome b5., Falzone CJ, Mayer MR, Whiteman EL, Moore CD, Lecomte JT, Biochemistry. 1996 May 28;35(21):6519-26. PMID:8639599
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