Biomaterial Database

Tryptophan-136 in subunit II of cytochrome bo3 from Escherichia coli may participate in the binding of ubiquinol. 1998

J Ma, and A Puustinen, and M Wikström, and R B Gennis

Department of Biochemistry, University of Illinois, Urbana 61801, USA.

In the cytochrome c oxidases, the role of subunit II is to provide the electron entry site into the enzyme. This subunit contains both the binding site for the substrate, cytochrome c, and the CuA redox center, which is initially reduced by cytochrome c. Cytochrome bo3 and other quinol oxidases that are members of the heme-copper oxidase superfamily have a homologous subunit II, but the CuA site is absent, as is the docking site for cytochrome c. Speculation that subunit II in the quinol oxidases may also be important as an electron entry site is supported by the demonstration several years ago that a photoreactive substrate analogue, azido-Q, covalently labeled subunit II in cytochrome bo3. In the current work, a sequence alignment of subunit II of heme-copper quinol oxidases is used as a guide to select conserved residues that might be important for the binding of ubiquinol to cytochrome bo3. Results are presented for point mutants in 24 different residue positions in subunit II. The membrane-bound enzymes were examined by optical spectroscopy and by determining the activity of ubiquinol-1 oxidase. In each case, the Km for ubiquinol-1 was determined as a measure of possible perturbation to a quinol binding site. The only mutant that had a noticeably altered Km for ubiquinol-1 was W136A, in which the Km was about sixfold increased. Thus, W136 may be at or close to a substrate (ubiquinol)-binding site in cytochrome bo3. In the cytochrome c oxidases, the equivalent tryptophan (W121 in Paracoccus denitrificans) has been identified as the "electron entry site".

UI	MeSH Term	Description	Entries
D008958	Models, Molecular	Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.	Molecular Models,Model, Molecular,Molecular Model
D008969	Molecular Sequence Data	Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.	Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D010088	Oxidoreductases	The class of all enzymes catalyzing oxidoreduction reactions. The substrate that is oxidized is regarded as a hydrogen donor. The systematic name is based on donor:acceptor oxidoreductase. The recommended name will be dehydrogenase, wherever this is possible; as an alternative, reductase can be used. Oxidase is only used in cases where O2 is the acceptor. (Enzyme Nomenclature, 1992, p9)	Dehydrogenases,Oxidases,Oxidoreductase,Reductases,Dehydrogenase,Oxidase,Reductase
D003573	Cytochrome b Group	Cytochromes (electron-transporting proteins) with protoheme (HEME B) as the prosthetic group.	Cytochromes Type b,Cytochromes, Heme b,Group, Cytochrome b,Heme b Cytochromes,Type b, Cytochromes,b Cytochromes, Heme,b Group, Cytochrome
D003580	Cytochromes	Hemeproteins whose characteristic mode of action involves transfer of reducing equivalents which are associated with a reversible change in oxidation state of the prosthetic group. Formally, this redox change involves a single-electron, reversible equilibrium between the Fe(II) and Fe(III) states of the central iron atom (From Enzyme Nomenclature, 1992, p539). The various cytochrome subclasses are organized by the type of HEME and by the wavelength range of their reduced alpha-absorption bands.	Cytochrome
D004926	Escherichia coli	A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.	Alkalescens-Dispar Group,Bacillus coli,Bacterium coli,Bacterium coli commune,Diffusely Adherent Escherichia coli,E coli,EAggEC,Enteroaggregative Escherichia coli,Enterococcus coli,Diffusely Adherent E. coli,Enteroaggregative E. coli,Enteroinvasive E. coli,Enteroinvasive Escherichia coli
D000595	Amino Acid Sequence	The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.	Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D001386	Azides	Organic or inorganic compounds that contain the -N3 group.	Azide
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D014364	Tryptophan	An essential amino acid that is necessary for normal growth in infants and for NITROGEN balance in adults. It is a precursor of INDOLE ALKALOIDS in plants. It is a precursor of SEROTONIN (hence its use as an antidepressant and sleep aid). It can be a precursor to NIACIN, albeit inefficiently, in mammals.	Ardeydorm,Ardeytropin,L-Tryptophan,L-Tryptophan-ratiopharm,Levotryptophan,Lyphan,Naturruhe,Optimax,PMS-Tryptophan,Trofan,Tryptacin,Tryptan,Tryptophan Metabolism Alterations,ratio-Tryptophan,L Tryptophan,L Tryptophan ratiopharm,PMS Tryptophan,ratio Tryptophan