1fcb
MOLECULAR STRUCTURE OF FLAVOCYTOCHROME B2 AT 2.4 ANGSTROMS RESOLUTION
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OverviewOverview
The crystal structure of flavocytochrome b2 has been solved at 3.0 A, resolution by the method of multiple isomorphous replacement with, anomalous scattering. Area detector data from native and two heavy-atom, derivative crystals were used. The phases were refined by the B.C. Wang, phase-filtering procedure utilizing the 67% (v/v) solvent content of the, crystals. A molecular model was built first on a minimap and then on, computer graphics from a combination of maps both averaged and not, averaged about the molecular symmetry axis. The structure was extended to, 2.4 A resolution using film data recorded at a synchrotron and refined by, the Hendrickson-Konnert procedure. The molecule, a tetramer of Mr 230,000, is located on a crystallographic 2-fold axis and possesses local 4-fold, symmetry. Each subunit is composed of two domains, one binding a heme and, the other an FMN prosthetic group. In subunit 1, both the cystochrome and, the flavin-binding domain are visible in the electron density map. In, subunit 2 the cytochrome domain is disordered. However, in the latter, a, molecule of pyruvate, the product of the enzymatic reaction, is bound at, the active site. The cytochrome domain consists of residues 1 to 99 and is, folded in a fashion similar to the homologous soluble fragment of, cytochrome b5. The flavin binding domain contains a parallel beta 8 alpha, 8 barrel structure and is composed of residues 100 to 486. The remaining, 25 residues form a tail that wraps around the molecular 4-fold axis and is, in contact with each remaining subunit. The FMN moiety, which is located, at the C-terminal end of the central beta-barrel, is mostly sequestered, from solvent; it forms hydrogen bond interactions with main- and, side-chain atoms from six of the eight beta-strands. The interaction of, Lys349 with atoms N-1 and O-2 of the flavin ring is probably responsible, for stabilization of the anionic form of the flavin semiquinone and, hydroquinone and enhancing the reactivity of atom N-5 toward sulfite. The, binding of pyruvate at the active site in subunit 2 is stabilized by, interaction of its carboxylate group with the side-chain atoms of Arg376, and Tyr143. Residues His373 and Tyr254 interact with the keto-oxygen atom, and are involved in catalysis. In contrast, four water molecules occupy, the substrate-binding site in subunit 1 and Tyr143 forms a hydrogen bond, to the ordered heme propionate group. Otherwise the two flavin-binding, domains are identical within experimental error.(ABSTRACT TRUNCATED AT 400, WORDS)
About this StructureAbout this Structure
1FCB is a Single protein structure of sequence from Saccharomyces cerevisiae with HEM, FMN and PYR as ligands. Active as L-lactate dehydrogenase (cytochrome), with EC number 1.1.2.3 Full crystallographic information is available from OCA.
ReferenceReference
Molecular structure of flavocytochrome b2 at 2.4 A resolution., Xia ZX, Mathews FS, J Mol Biol. 1990 Apr 20;212(4):837-63. PMID:2329585
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