Studying Food Reward and Motivation in Humans

A key challenge in studying reward processing in humans is to go beyond subjective self-report measures and quantify different aspects of reward such as hedonics, motivation, and goal value in more objective ways. This is particularly relevant for the understanding of overeating and obesity as well as their potential treatments. In this paper are described a set of measures of food-related motivation using handgrip force as a motivational measure. These methods can be used to examine changes in food related motivation with metabolic (satiety) and pharmacological manipulations and can be used to evaluate interventions targeted at overeating and obesity. However to understand food-related decision making in the complex food environment it is essential to be able to ascertain the reward goal values that guide the decisions and behavioral choices that people make. These values are hidden but it is possible to ascertain them more objectively using metrics such as the willingness to pay and a method for this is described. Both these sets of methods provide quantitative measures of motivation and goal value that can be compared within and between individuals.     

Expression enhancement of bubaline somatotropin in E. coli through gene modifications in the 5'-end coding region

This study addresses the problem of poor expression of somatotropin (ST) gene in E. coli and describes expression enhancement through silent and non-silent gene modifications. A series of constructs with codon optimization, substitution, deletion or addition in the 5'-region of the sequence encoding bubaline ST (BbST) were prepared. In the native form, the BbST expression was barely discernible on SDS-gel of the total E. coli cellular proteins (TCP). Introduction of silent and non-silent mutations in +2 to +8 codons, however, raised the expression levels to varying extents. In some constructs, a single base variation, i.e., G-->A or G-->C led to a remarkable increase in BbST expression (up to 28% of the TCP) whereas in the case of G-->T substitution the expression dropped to undetectable levels. Deletion of native GCC codon and addition of CAUCAC repeat thrice at +2 position enhanced the expression up to 48%, while insertion of NGG codons at the same position caused just a modest increase in expression. Differences in expression appeared as if related to the nature of early downstream codons (especially +2) and the stability of mRNA secondary structure although the levels of intracellular mRNA pools, as analyzed by real-time RT-PCR were quite similar. Overall, the study highlights the importance of 5'-end codon adaptations in solving the problems encountered in expressing the eukaryotic genes in E. coli.     

Synonymous codon changes at the 5′-end of the gene strongly impact the heterologous protein expression in <Emphasis Type="Italic">Escherichia coli</Emphasis>

This study describes the impact of 5′-end codon modulation on the expression of a heterologous gene, human granulocyte colony stimulating factor (GCSF), in Escherichia coli. Fourteen different constructs (pGCSF-01 to pGCSF-14) carrying single or multiple synonymous substitutions at +2, +3 and further down from +4 to +7 codons, were prepared and their expression was monitored in E. coli BL21 Codon-Plus (DE3) RIPL using a strong T7 lac-promoter based expression system. A single nucleotide change at +2 Thr codon (ACC→ACA) either alone or in combination with +3 Pro codon (CCC/CCT/CCA) resulted in the expression enhancement of an otherwise poorly expressed native-GCSF, to a level that corresponded to 45–50% of the total E. coli BL21 CodonPlus (DE3) RIPL cellular proteins. The differences in GCSF expression amongst different constructs could be attributed to the preferential or non-preferential codon usage, reduced number of G/C nucleotides and the stability of mRNA secondary structure formed near the 5′-end coding region. The expression of GCSF achieved was in the form of biologically inactive inclusion bodies that were solubilized using mild concentration of a non-ionic surfactant and refolded by a simplified, step-dialysis approach. Biological activity of the purified GCSF, assessed in induced neutropenic mice, was similar to the commercially available preparation of the GCSF analog (filgrastim).     

The protonation-deprotonation kinetics of the protonated Schiff base in bicelle bacteriorhodopsin crystals

In the recently published x-ray crystal structure of the "bicelle" bacteriorhodopsin (bbR) crystal, the protein has quite a different structure from the native and the in cubo bacteriorhodopsin (cbR) crystal. Instead of packing in parallel trimers as do the native membrane and the cbR crystals, in the bbR crystal the protein packs as antiparallel monomers. To date, no functional studies have been performed, to our knowledge, to investigate if the photocycle is observed in this novel protein packing structure. In this study, both Raman and time-resolved transient absorption spectroscopy are used to both confirm the presence of the photocycle and investigate the deprotonation-reprotonation kinetics of the Schiff base proton in the bbR crystal. The observed rates of deprotonation and reprotonation processes of its Schiff base have been compared to those observed for native bR under the same conditions. Unlike the previously observed similarity of the rates of these processes for cbR crystals and those for native bacteriorhodopsin (bR), in bbR crystals the rate of deprotonation has increased by 300%, and the rate of reprotonation has decreased by nearly 700%. These results are discussed in light of the changes observed when native bR is delipidated or monomerized by detergents. Both the change of the hydrophobicity of the environment around the protonated Schiff base and Asp85 and Asp96 (which could change the pKa values of proton donor-acceptor pairs) and the water structure in the bbR crystal are offered as possible explanations for the different observations.     

Isolation, characterization and kinetics of goat cystatins

Two cysteine proteinase inhibitors I and II were purified from goat kidney using alkaline denaturation, ammonium sulphate fractionation, gel filtration on Sephadex G-75 and ion exchange chromatography on DEAE cellulose. The purified inhibitors were homogenous and showed a single band on SDS PAGE under reducing and non-reducing conditions with an apparent molecular mass of 67 kDa. The cystatin forms were stable in the range of pH 3–10 and up to 95 °C. Immunological identity with the sheep LMW kininogen was obtained suggesting that the inhibitor is closely related to kininogens. Spectral studies confirm that the inhibitors have predominantly an α-helical structure and undergo major conformational changes during complex formation with papain. The inhibitors had similar inhibitory activities on cysteine proteinases. Both inhibitors inhibited papain, ficin and bromelain competitively, with maximum affinity for papain. The overall lower affinity of these inhibitors to cysteine proteinases compared to other known cystatins can be attributed to the unusual N-terminal sequence where Leu is substituted by Ile. Furthermore, N-terminal sequence analysis revealed maximum homology to mammalian LMW kininogen.