Biomedical subjects

Julian A Peterson

Publications and source records attributed to Julian A Peterson.

4 recordsLinked to original sources

PubMed2005

LXRs regulate the balance between fat storage and oxidation.

Despite the well-established role of liver X receptors (LXRs) in regulating cholesterol homeostasis, their contribution to lipid homeostasis remains unclear. Here we show that LXR null mice are defective in hepatic lipid metabolism and are resistant to obesity when challenged with a diet containing both high fat and cholesterol. This phenotype is dependent on the presence of dietary cholesterol and is accompanied by the aberrant production of thyroid hormone in liver. Interestingly, the inability of LXR-/- mice to induce SREBP-1c-dependent lipogenesis does not explain the LXR-/- phenotype, since SREBP-1c null mice are not obesity resistant. Instead, the LXR-/- response is due to abnormal energy dissipation resulting from uncoupled oxidative phosphorylation and ectopic expression of uncoupling proteins in muscle and white adipose. These studies suggest that, by selectively sensing the cholesterol component of a lipid-rich diet, LXRs govern the balance between storage and oxidation of dietary fat.

Adipose Tissue↗

PubMed2002

A new approach to the study of protein-protein interaction by FTIR: complex formation between cytochrome P450BM-3 heme domain and FMN reductase domain.

We describe a new approach to the study of protein-protein interaction using Fourier transform infrared spectroscopy (FTIR). This approach is based on the combination of FTIR technique with both protein titration experiments and the principal component analysis (factor analysis) of the IR absorption spectra in the 1500-1800 cm(-1) region for the protein mixtures. We have applied this approach to the interaction of the heme domain with the FMN domain of bacterial monooxygenase cytochrome P450BM-3 (CYP102A1). The analysis reveals that the first principal component reflects the protein-protein complex formation because the loading factors show a clear systematic dependence on the concentration of the heme domain according to a titration curve with a dissociation constant of approximately 5 microM. The spectrum of the first principal component has been assigned to structural changes in the secondary structure (increase of beta-sheet and alpha-helix and decrease of turn structures), amino acid side chains (protonation of aspartate and C-terminal COO group), and deprotonation of a propionic acid COOD group in the heme.

Bacillus megaterium↗

PubMed2002

Probing the interaction of bovine cytochrome P450scc (CYP11A1) with adrenodoxin: evaluating site-directed mutations by molecular modeling.

The present study was undertaken to evaluate the role of positively charged amino acid residues proposed to reside on the proximal surface of bovine cytochrome P450 cholesterol side chain cleavage (P450scc, CYP11A1) and to determine which residues may be involved in protein-protein interactions with the electron carrier adrenodoxin (Adx). In previous studies, nine different lysine residues were identified by chemical and immunological cross-linking experiments as potentially interacting with Adx, while in the present study, two arginine residues have been identified from sequence alignments. From these 11 residues, 13 different P450scc mutants were made of which only seven were able to be expressed and characterized. Each of the seven mutants were evaluated for their ability to bind Adx, to be reduced, and for their enzymatic activity. Among these, K403Q and K405Q showed a consistent decrease in Adx binding, the ability to be reduced by Adx, and enzymatic activity, with K405Q being affected to a much greater extent. More dramatic was the complete loss of Adx binding by R426Q, while still retaining its ability to be chemically reduced and bind carbon monoxide. Independently, a homology model of P450scc was constructed and docked with the structure of Adx. Four potential sites of interaction were identified: P450scc:K403 with Adx:D76, P450scc:K405 with Adx:D72; P450scc:R426 with Adx:E73, and P450scc:K267 with Adx:E47. Thus, the biochemical and molecular modeling studies together support the hypothesis that K267, K403, K405, and R426 participate in the electrostatic interaction of P450scc with Adx.

Adrenodoxin↗

PubMed2002

Sequence alignments, variabilities, and vagaries.

It seems as if the algorithms and weighting matrices for multiple sequence alignments of the highly divergent members of the P450 gene superfamily have advanced to the point that unknown proteins can be aligned to structurally known members with reasonable accuracy. As stated earlier, the alignment tends to break down at gaps in the sequence alignments, but these regions can be improved manually. This type of alignment and analysis is especially useful for extracting and analyzing the various genome databases. Variations of the conservation analysis can be used to identify charged and uncharged residues that may be important in domain/domain interactions with redox partners or effector molecules (e.g., cytochrome b5). From these alignments and with comparative analysis within families and across P450 families, one can readily obtain an estimation of those residues that might be involved in substrate binding, in redox partner interaction, and in the catalytic mechanism.

Amino Acid Sequence↗