Functional characterization of cytochromes P450 2B from the desert woodrat Neotoma lepida

Mammalian detoxification processes have been the focus of intense research, but little is known about how wild herbivores process plant secondary compounds, many of which have medicinal value or are drugs. cDNA sequences that code for three enzymes of the cytochrome P450 (CYP) 2B subfamily, here termed 2B35, 2B36, and 2B37 have been recently identified from a wild rodent, the desert woodrat (Malenke et al., 2012). Two variant clones of each enzyme were engineered to increase protein solubility and to facilitate purification, as reported for CYP2B enzymes from multiple species. When expressed in Escherichia coli each of the woodrat proteins gave the characteristic maximum at 450nm in a reduced carbon monoxide difference spectrum but generally expressed at lower levels than rat CYP2B1. Two enzymes, 2B36 and 2B37, showed dealkylation activity with the model substrates 7-ethoxy-4-(trifluoromethyl)coumarin and 7-benzyloxyresorufin, whereas 2B35 was inactive. Binding of the monoterpene (+)-α-pinene produced a Type I shift in the absorbance spectrum of each enzyme. Mutation of 2B37 at residues 114, 262, or 480, key residues governing ligand interactions with other CYP2B enzymes, did not significantly change expression levels or produce the expected functional changes. In summary, two catalytic and one ligand-binding assay are sufficient to distinguish among CYP2B35, 2B36, and 2B37. Differences in functional profiles between 2B36 and 2B37 are partially explained by changes in substrate recognition site residue 114, but not 480. The results advance our understanding of the mechanisms of detoxification in wild mammalian herbivores and highlight the complexity of this system.

Different phosphorylation rates among vertebrate cone visual pigments with different spectral sensitivities

Cone photoreceptor subtypes having different spectral sensitivities exhibit different recovery kinetics in their photoresponses in some vertebrates. Phosphorylation by G protein-coupled receptor kinase (GRK) is essential for the rapid inactivation of light-activated visual pigment, which is the rate-limiting step of the cone photoresponse recovery in salamander. In this study we compared the rate of light-dependent phosphorylation by GRK7 of carp green- and blue-sensitive cone visual pigments. Blue pigment was phosphorylated significantly less effectively than green pigment, suggesting that the difference in the pigment phosphorylation rate is responsible for the difference in photoresponse kinetics among cone photoreceptor subtypes.

Analysis of protein expression in zebrafish during gonad differentiation by targeted proteomics

The molecular mechanisms governing sex determination and differentiation in the zebrafish (Danio rerio) are not fully understood. To gain more insights into the function of specific genes in these complex processes, the expression of multiple candidates needs to be assessed, preferably on the protein level. Here, we developed a targeted proteomics method based on selected reaction monitoring (SRM) to study the candidate sex-related proteins in zebrafish which were selected based on a global proteomics analysis of adult gonads and representational difference analysis of male and female DNA, as well as on published information on zebrafish and other vertebrates. We employed the developed SRM protocols to acquire time-resolved protein expression profiles during the gonad differentiation period in vas::EGFP transgenic zebrafish. Evidence on protein expression was obtained for the first time for several candidate genes previously studied only on the mRNA level or suggested by bioinformatic predictions. Tuba1b (tubulin alpha 1b), initially included in the study as one of the potential housekeeping proteins, was found to be preferentially expressed in the adult testis with nearly absent expression in the ovary. The revealed changes in protein expression patterns associated with gonad differentiation suggest that several of the examined proteins, especially Ilf2 and Ilf3 (interleukin enhancer-binding factors 2 and 3), Raldh3 (retinaldehyde dehydrogenase type 3), Zgc:195027 (low density lipoprotein-related receptor protein 3) and Sept5a (septin 5a), may play a specific role in the sexual differentiation in zebrafish.

In vivo modulation of polo-like kinases supports a key role for PLK2 in Ser129 α-synuclein phosphorylation in mouse brain

α-Synuclein is the major component of Lewy bodies. α-Synuclein phosphorylated at Ser 129 (Phospho-α-Syn) is the most common synuclein modification observed in Parkinson's disease pathology and transgenic animal models. Polo-like kinase 2 (PLK2) was previously proposed as an important kinase in α-synuclein phosphorylation at Ser129. To better understand the role of PLK2 in α-synuclein phosphorylation in vivo, we further evaluated the effect of PLK2 genetic knockdown and pharmacological inhibition on Phospho-α-Syn levels in different brain regions of PLK2 knockout (KO), heterozygous (Het) and wild-type (WT) mice. Whereas PLK2 knockdown had no effect on Total-α-synuclein brain levels, it resulted in a gene-dosage dependent, albeit incomplete, reduction of endogenous Phospho-α-Syn levels in all brain regions investigated. No compensatory induction of other α-synuclein kinases (PLK3, casein kinase-2, G-protein-coupled receptor kinase 5 (GRK5) and GRK6) was observed at the mRNA level in the PLK2 KO mouse brain. To determine whether increased activity of another PLK family member is responsible for the residual Phospho-α-Syn levels in the PLK2 KO mouse brain, the pan-PLK inhibitor BI 2536 was tested in PLK2 KO mice. Whereas BI 2536 reduced Phospho-α-Syn levels in WT mice, it did not further reduce the residual endogenous Phospho-α-Syn levels in PLK2 KO and Het mice, suggesting that a kinase other than PLK1-3 accounts for the remaining PLK inhibitor-resistant pool in the mouse brain. Moreover, PLK3 KO in mice had no effect on both Total- and Phospho-α-Syn brain levels. These results support a significant role for a PLK kinase in phosphorylating α-synuclein at Ser129 in the brain, and suggest that PLK2 is responsible for this activity under physiological conditions.

Identification of voltage-gated K(+) channel beta 2 (Kvβ2) subunit as a novel interaction partner of the pain transducer Transient Receptor Potential Vanilloid 1 channel (TRPV1)

The Transient Receptor Potential Vanilloid 1 (TRPV1, vanilloid receptor 1) ion channel plays a key role in the perception of thermal and inflammatory pain, however, its molecular environment in dorsal root ganglia (DRG) is largely unexplored. Utilizing a panel of sequence-directed antibodies against TRPV1 protein and mouse DRG membranes, the channel complex from mouse DRG was detergent-solubilized, isolated by immunoprecipitation and subsequently analyzed by mass spectrometry. A number of potential TRPV1 interaction partners were identified, among them cytoskeletal proteins, signal transduction molecules, and established ion channel subunits. Based on stringent specificity criteria, the voltage-gated K(+) channel beta 2 subunit (Kvβ2), an accessory subunit of voltage-gated K(+) channels, was identified of being associated with native TRPV1 channels. Reverse co-immunoprecipitation and antibody co-staining experiments confirmed TRPV1/Kvβ2 association. Biotinylation assays in the presence of Kvβ2 demonstrated increased cell surface expression levels of TRPV1, while patch-clamp experiments resulted in a significant increase of TRPV1 sensitivity to capsaicin. Our work shows, for the first time, the association of a Kvβ subunit with TRPV1 channels, and suggests that such interaction may play a role in TRPV1 channel trafficking to the plasma membrane.

Solution NMR studies of cell-penetrating peptides in model membrane systems

Cell-penetrating peptides (CPPs) are a class of short, often cationic peptides that have the capability to translocate across cellular membranes, and although the translocation most likely involves several pathways, they interact directly with membranes, as well as with model bilayers. Most CPPs attain a three-dimensional structure when interacting with bilayers, while they are more or less unstructured in aqueous solution. To understand the relationship between structure and the effect that CPPs have on membranes it is of great importance to investigate CPPs at atomic resolution in a suitable membrane model. Moreover, the location in bilayers is likely to be correlated with the translocation mechanism. Solution-state NMR offers a unique possibility to investigate structure, dynamics and location of proteins and peptides in bilayers. This review focuses on solution NMR as a tool for investigating CPP-lipid interactions. Structural propensities and cell-penetrating capabilities can be derived from a combination of CPP solution structures and studies of the effect that the peptides have on bilayers and the localization in a bilayer.