Welcome to the Boutis research laboratory web page. We are an experimental condensed matter and biophysics group. At the moment, our interest focuses largely on elastin and elastomeric proteins. Examples of abstracts from some of our recent work are provided below.
Ukpebor,O.T., A. Shah, E. Bazov, G.S. Boutis "Inverse Temperature Transition of Elastin Like Motifs in Major Ampullate Dragline Silk: MD Simulations of Short Peptides and NMR Studies of Water Dynamics" Accepted for publication in Soft Matter.
Using deuterium 2D T1-T2 Inverse Laplace Transform (ILT) NMR we have investigated the distribution, population, and dynamics of waters of hydration in major ampullate N. clavipes and A. aurantia silk as a function of temperature. In both samples studied, correlation times much larger than that of free water are measured and in some cases appear to increase with increasing temperature over the range of 5 to 60 C(corresponding to reduced tumbling). In addition, the experimental data point to a reduction in the population of water localized in the silk with increasing temperature in the range of 20 to 50C. Molecular dynamics simulations were performed to probe the thermal characteristics of a variety of repeating motifs found in the two silk samples. The repeating motifs GLGSQ, GAAAAAAG, GPGGY, GPGQQ, GPSG, and GPSGPGS found in N. clavipes, GLGSQ, GYGSG, GPGSG, and GPGSQ found in A. aurantia silk were found to exhibit a thermal property observed in short elastin peptides known as the ``inverse temperature transition''. This is a well known characteristic exhibited by short peptides consisting of (VPGXG)n motifs (where X is any amino acid other than proline) found in elastin, a protein responsible for the elasticity of vertebrate tissues. In qualitative agreement with experimental measurements of water in the silks, all the peptides studied in simulation show evidence of an increase in sidechain contacts and peptide hydrogen bonds, concomitant with a decrease in radius of gyration and localized water as the temperature is raised from approximately 5 to 60C.
Downing, K., M. Billah, E. Raparia, A. Shah, M. Silverstein, A. Ahmad, G.S. Boutis "The role of mode of delivery on elastic fiber architecture and vaginal vault elasticity: a rodent model study" Accepted for publication in the Journal of the Mechanical Behavior of Biomedical Materials.PDF
We report on an experimental study of the role of mode of delivery and pregnancy on the architecture of vaginal elastic fibers and
vaginal vault elasticity in female Sprague-Dawley rats. In primiparous rats submitted to spontaneous or Cesarean delivery and
virgin rats submitted to simulated delivery, the tortuosity of elastic fibers (defined as the ratio of length to end-to-end
distance) was observed to decrease when measured two days to two weeks postpartum. In addition, the measured tortuosity of elastic
fibers in multiparous rats was greater than that of virgin rats. The tortuosity of elastic fibers of all rats measured at two
days postpartum were found to be similar to that of multiparous rats. At two weeks postpartum the measured tortuosity of vaginal
elastic fibers was indistinguishable from virgin rats, regardless of the delivery method. Borrowing from the field of polymer
physics, a model is suggested that connects elastic fiber tortuosity to the resulting tension under an applied stress; fibers having
high tortuosity are expected to provide less structural support than more linear, low tortuosity fibers. To probe the
macroscopic effects in elasticity due to architectural changes observed in elastic fibers, we have measured the stiffness of the
vaginal vault in each cohort using a pressure-infusion system. The vaginal vault stiffness of all primiparous rats
measured two weeks postpartum was greater than that measured two days postpartum. In addition, the vaginal vault of virgin rats was
stiffer than that of multiparous rats. These observations confirmed that vaginal vault elastic fibers undergo significant
remodeling due to pregnancy and parturition, and that the complex remodeling may be a significant contributor to tissue elasticity.
Remarkably, regardless of the mode of delivery or simulated tissue trauma, elastic fiber tortuosity is observed to decrease from
two days to two weeks postpartum indicating the onset of repair and recovery of tissue stiffness.
Zelenova, Y., S. W. Morgan, G. S. Boutis, "Effects of experimental imperfections on a spin counting experiment" Solid State Nucl. Magn. Reson. 53, 27-37 2013. PDF
Spin counting NMR is an experimental technique that allows a determination of the size and time evolution of networks of dipolar coupled nuclear spins. This work reports on an average Hamiltonian treatment of two spin counting sequences and compares the efficiency of the two cycles in the presence of flip errors, RF inhomogeneity, phase transients, and phase errors commonly present in NMR experiments. Simulations on small quantum systems performed using the two cycles reveal the effects of pulse imperfections on the resulting multiple quantum spectra, in qualitative agreement with the average Hamiltonian calculations. Experimental results on adamantane are presented, demonstrating differences in the two sequences in the presence of pulse errors.
C. Sun, O. Mitchell, J. Huang, G. S. Boutis. "NMR Studies of Localized Water and Protein Backbone Dynamics in Mechanically Strained Elastin" J. Phys. Chem. B, 115 (47), 13935-13942. 2011
We report on measurements of the dynamics of localized waters of hydration and the protein backbone of elastin, a remarkable resilient protein found in vertebrate tissues, as a function of the applied external strain. Using deuterium 2D T1-T2 NMR, we separate four reservoirs in the elastin-water system characterized by water with distinguishable mobilities. The measured correlation times corresponding to random tumbling of water localized to the protein is observed to decrease with increasing strain and is interpreted as an increase in its orientational entropy. The NMR T1and T1r relaxation times of the carbonyl and aliphatic carbons of the protein backbone are measured and indicate a reduction in the correlation time as the elastomer strain is increased. It is argued, and supported by MD simulation of a short model elastin peptide [VPGVG]3, that the observed changes in the backbone dynamics gives rise to the development of an entropic elastomeric force that is responsible for elastins' remarkable elasticity.
Ma, X., C. Sun, J. Huang, G.S. Boutis. "Thermal Hysteresis in the Backbone and Side Chain Dynamics of the Elastin Mimetic Peptide [VPGVG]3 Revealed by 2H NMR." J. Phys. Chem. B.116 (1),555–564. 2012
We report on experimental measurements of the backbone and side chain dynamics of the elastin mimetic peptide [VPGVG]3 by 2H NMR echo spectroscopy and 2D T-T2 correlation relaxometry. The T1 and T2 relaxation times of the Gly alpha-deuterons and Val alpha-, beta- and gamma-deuterons of a hydrated sample reveal a thermal hysteresis when the temperature is raised from -10C to 45C and then subsequently cooled back to -10C. In addition, near 30C we observe a reduction in the slope of the T1(T) and T2(T) heating curves, indicating a structural change that appears to be correlated well to the known inverse temperature transition of this peptide. The thermal dependence of the correlation times of the Gly alpha-deuterons are well fit by an Arrhenius Law, from which we have measured Eact=(20.0 +/- 3.1) kJ/mol when the sample is heated, and Eact=(10.9 +/- 2.8) kJ/mol when cooled. Molecular dynamics simulations support the notion that the measured activation energy is determined largely by the extent of localized water, which is observed to decrease with increasing temperature from approximately 25C to 42C.