Oskar Liivak

Orientation, structure, wet-spinning, and molecular basis for supercontraction of spider dragline silk

This manuscript reviews work from our laboratory that addresses the orientation, secondary structure, wet-spinning, and molecular basis for supercontraction of spider silk. It identifies the poly(alanine) runs as the crystalline regions, establishes the degree of orientation of these regions, and identifies the secondary structural elements of the conserved L-G-X-Q (X = G, S, or N) regions. It also describes methods for spinning very small amounts of protein polymers and it sets forth several molecular-level hypotheses concerning supercontraction.

Multiple simultaneous distance determinations: Application of rotational echo double resonance nuclear magnetic resonance to IS2 spin networks

Rotational Echo DOuble Resonance (REDOR) NMR is an oft-demonstrated tool for measuring distance between isolated IS spin pairs. Its application to more complex ISn spin networks (n>1), however, is rare, as in these systems the interpretation of the results is model-dependent–while it is precisely the measurement of multiple distances which is required for molecular structure elucidation. Recently, Θ-REDOR was introduced and was shown to improve interpretability at the cost of signal intensity. In this paper we analyze generalizations to the REDOR pulse sequence, and present a new experimental procedure which allows for simultaneous distance determinations in larger spin systems with improved signal intensity. Experimental data are presented for the IS2 spin system glycine-13C2-15N.

Rotational echo double resonance in ISN spin networks: Deconvolution of multiple dipole–dipole couplings

In a recent paper we have demonstrated how a simple modification to the standard rotational echo double resonance pulse sequence, where the flip angle of the pulse applied to the S spin is varied, can be used to separate the measurement of the magnitude of I–S dipole–dipole couplings from that of their relative orientation. An equivalent result can be achieved via phase modulation which labels and differentiates between different evolving coherences in the density matrix based on the number of S spins participating—exactly as is done in multiple quantum spectroscopy. As phase modulation can be effected on modern instruments with much higher precision, in this paper we explore the experimental implementation of this method in the IS2 spin system glycine–13C2–15N, and discuss generalizations of this technique to larger spin systems.