2 research outputs found
Type and Amount of Lipids Influence the Molecular and Textural Properties of a Soy Soft Pretzel
Altering baked goods by the addition
of nutrient-rich ingredients,
such as soy and ground almonds, affects the water and lipid distribution
of the product and, subsequently, its final quality. Here, we studied
how three lipid sources, shortening, canola oil, and ground almonds,
affected texture and water distribution in a baked soy pretzel and
the molecular mobility in the dough. Pretzel crumb from all formulations
exhibited 40–43% moisture with a little more than half present
as “freezable” water. Firmness and chewiness decreased
with increased shortening and canola oil, whereas firmness and chewiness
increased with additional almonds. In contrast, neither springiness
nor cohesiveness was affected by the lipid quantity or source. Finally,
magnetic resonance imaging of the soy pretzel dough revealed two or
three populations of dough components that have distinct molecular
mobilities. With increased lipid content, the mobility of each population
increased in magnitude and heterogeneity. Interestingly, almonds had
the smallest effect on the molecular mobility of the dough but had
the largest effect on textural properties. These results provide quantitative
insight into the mechanisms by which the lipid source can influence
molecular properties that have textural implications for bakery products
Homotropic Cooperativity from the Activation Pathway of the Allosteric Ligand-Responsive Regulatory <i>trp</i> RNA-Binding Attenuation Protein
The <i>trp</i> RNA-binding attenuation protein (TRAP) assembles into
an 11-fold symmetric ring that regulates transcription and translation
of <i>trp</i>-mRNA in bacilli via heterotropic allosteric
activation by the amino acid tryptophan (Trp). Whereas nuclear magnetic
resonance studies have revealed that Trp-induced activation coincides
with both microsecond to millisecond rigidification and local structural
changes in TRAP, the pathway of binding of the 11 Trp ligands to the
TRAP ring remains unclear. Moreover, because each of 11 bound Trp
molecules is completely surrounded by protein, its release requires
flexibility of Trp-bound (holo) TRAP. Here, we used stopped-flow fluorescence
to study the kinetics of Trp binding by <i>Bacillus stearothermophilus</i> TRAP over a range of temperatures and observed well-separated kinetic
steps. These data were analyzed using nonlinear least-squares fitting
of several two- and three-step models. We found that a model with
two binding steps best describes the data, although the structural
equivalence of the binding sites in TRAP implies a fundamental change
in the time-dependent structure of the TRAP rings upon Trp binding.
Application of the two-binding step model reveals that Trp binding
is much slower than the diffusion limit, suggesting a gating mechanism
that depends on the dynamics of apo TRAP. These data also reveal that
dissociation of Trp from the second binding mode is much slower than
after the first Trp binding mode, revealing insight into the mechanism
for positive homotropic allostery, or cooperativity. Temperature-dependent
analyses reveal that both binding modes imbue increases in bondedness
and order toward a more compressed active state. These results provide
insight into mechanisms of cooperative TRAP activation and underscore
the importance of protein dynamics for ligand binding, ligand release,
protein activation, and allostery