NMR-based metabolomics and breath studies show lipid and protein catabolism during low dose chronic T(1)AM treatment.

OBJECTIVE: 3-Iodothyronamine (T1 AM), an analog of thyroid hormone, is a recently discovered fast-acting endogenous metabolite. Single high-dose treatments of T1 AM have produced rapid short-term effects, including a reduction of body temperature, bradycardia, and hyperglycemia in mice. DESIGN AND METHODS: The effect of daily low doses of T1 AM (10 mg/kg) for 8 days on weight loss and metabolism in spontaneously overweight mice was monitored. The experiments were repeated twice (n = 4). Nuclear magnetic resonance (NMR) spectroscopy of plasma and real-time analysis of exhaled (13) CO2 in breath by cavity ring down spectroscopy (CRDS) were used to detect T1 AM-induced lipolysis. RESULTS: CRDS detected increased lipolysis in breath shortly after T1 AM administration that was associated with a significant weight loss but independent of food consumption. NMR spectroscopy revealed alterations in key metabolites in serum: valine, glycine, and 3-hydroxybutyrate, suggesting that the subchronic effects of T1 AM include both lipolysis and protein breakdown. After discontinuation of T1 AM treatment, mice regained only 1.8% of the lost weight in the following 2 weeks, indicating lasting effects of T1 AM on weight maintenance. CONCLUSIONS: CRDS in combination with NMR and (13) C-metabolic tracing constitute a powerful method of investigation in obesity studies for identifying in vivo biochemical pathway shifts and unanticipated debilitating side effects.

Efficient production of recombinant brazzein, a small, heat-stable, sweet-tasting protein of plant origin.

Brazzein is a 54-amino-acid sweet-tasting protein first isolated from the fruit of Pentadiplandra brazzeana Baillon found in West Africa. Brazzein, as isolated from the fruit, is 500 times sweeter than sucrose on a weight basis (9500 times sweeter on a per-molecule basis). A minor component of brazzein from fruit, des-pGlu1-brazzein, has 53 amino acid residues and has twice the sweetness of the parent protein. We have designed a gene for des-pGlu1- brazzein that incorporates codons that are optimal for protein production in Escherichia coli. Production of brazzein from the chemically synthesized gene resulted in recombinant protein with sweetness similar to that of brazzein isolated from the original source. The best yields were achieved by producing brazzein as a fusion with staphylococcal nuclease with a designed cyanogen bromide cleavage site. Because of its intense sweetness and stability at high pH and temperature, brazzein is an ideal system for investigating the chemical and structural requirements involved in sweet-taste properties. This efficient protein production system for brazzein will facilitate such investigations.

Sweetness determinant sites of brazzein, a small, heat-stable, sweet-tasting protein.

Brazzein, originally isolated from the fruit of the African plant Pentadiplandra brazzeana Baillon, is the smallest, most heat-stable and pH-stable member of the set of proteins known to have intrinsic sweetness. These properties make brazzein an ideal system for investigating the chemical and structural requirements of a sweet-tasting protein. We have used the three-dimensional structure of the protein (J. E. Caldwell et al. (1998) Nat. Struct. Biol. 5, 427-431) as a guide in designing 15 synthetic genes in expression constructs aimed at delineating the sweetness determinants of brazzein. Protein was produced heterologously in Escherichia coli, isolated, and purified as described in the companion paper (Assadi-Porter, F. M., Aceti, D., Cheng, H., and Markley, J. L., this issue). Analysis by one-dimensional (1)H NMR spectroscopy indicated that all but one of these variants had folded properly under the conditions used. A taste panel compared the gustatory properties of solutions of these proteins to those of sucrose and brazzein isolated from fruit. Of the 14 mutations in the des-pGlu1-brazzein background, four exhibited almost no sweetness, six had significantly reduced sweetness, two had taste properties equivalent to des-pGlu1-brazzein (two times as sweet as the major form of brazzein isolated from fruit which contains pGlu1), and two were about twice as sweet as des-pGlu1-brazzein. Overall, the results suggest that two regions of the protein are critical for the sweetness of brazzein: a region that includes the N- and C-termini of the protein, which are located close to one another, and a region that includes the flexible loop around Arg43.

Proton-translocating carboxyl of subunit c of F1Fo H(+)-ATP synthase: the unique environment suggested by the pKa determined by 1H NMR.

Subunit c of the H(+)-transporting F1Fo ATP synthase (EC 3.6.1.34) is thought to fold across the membrane as a hairpin of two alpha helices with a conserved Asp/Glu residue, centered in the second membrane-spanning helix, which is thought to function in H+ translocation. NMR studies indicate that the purified subunit c from Escherichia coli is also folded as a hairpin in a chloroform/methanol/H2O (4:4:1) solvent mixture [Girvin, M. E., & Fillingame, R. H. (1993) Biochemistry 32, 12167-12177] and that the conserved Asp remains uniquely reactive in this solvent mixture [Girvin, M. E., & Fillingame, R. H. (1994) Biochemistry 33, 665-674]. The pKa of Asp61 is of interest because of its unique reactivity and because it is thought to protonate and deprotonate during each proton translocation cycle. We have determined the pKa value of the carboxyl group of the functional Asp in wild type and two functional, mutant subunit c proteins, i.e. the Ala24-->Asp (D24D61) and the Ala24-->Asp/Asp61-->Asn (D24N61) mutant proteins. The pKa values were determined by 1H NMR spectroscopy by measuring changes in the alpha and beta proton chemical shifts by constant time two-dimensional (2D) correlated spectroscopy. The pKa of Asp61 in the purified wild type protein was 7.1. This pKa was significantly higher than the pKa of the other two Asp residues, i.e. Asp7 and Asp44 which were 5.4 and 5.6, respectively. The pKa of the two Glu residues in the protein were determined by 2D total correlation spectroscopy and found to be approximately 5.5.(ABSTRACT TRUNCATED AT 250 WORDS)