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A structural model for the nucleotide binding domains of the flavocytochrome b –245 β‐chain
Author(s) -
Taylor William R.,
Jones David T.,
Segal Anthony W.
Publication year - 1993
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560021013
Subject(s) - reductase , protein subunit , binding site , chemistry , biology , biochemistry , stereochemistry , gene , enzyme
NADPH is a system in phagocytic cells that generates O 2 − and hydrogen peroxide in the endocytic vacuole, both of which are important for killing of the engulfed microbe. Dysfunction of this oxidase results in the syndrome of chronic granulomatous disease, characterized by a profound predisposition to bacterial and fungal infections. A flavocytochrome b is the site of most of the mutations causing this syndrome. The FAD and NADPH binding sites have been located on the β subunit of this molecule, the C‐terminal half of which showed weak sequence similarity to other reductases, including the ferredoxin‐NADP reductase (FNR) of known structure. This enabled us to build a model of the nucleotide binding domains of the flavocytochrome using this structure as a template. The model was built initially using a novel automatic modeling method based on distance–matrix projection and then refined using energy minimization with appropriate side‐chain torsional constraints. The resulting model rationalized much of the observed sequence conservation and identified a large insertion as a potential regulatory domain. It confirms the inclusion of the neutrophil flavocytochrome b ‐245 (Cb‐245) as a member of the FNR family of reductases and strongly supports its function as the proximal electron transporting component of the NADPH oxidase.