| Abstract
| - Magic-angle spinning solid-state NMR (SSNMR) studies of the β1 immunoglobulin binding domainof protein G (GB1) are presented. Chemical shift correlation spectra at 11.7 T (500 MHz 1H frequency)were employed to identify signals specific to each amino acid residue type and to establish backboneconnectivities. High sensitivity and resolution facilitated the detection and assignment of every 15N and 13Csite, including the N-terminal (M1) 15NH3, the C-terminal (E56) 13C‘, and side-chain resonances from residuesexhibiting fast-limit conformational exchange near room temperature. The assigned spectra lend novelinsight into the structure and dynamics of microcrystalline GB1. Secondary isotropic chemical shifts reporton conformation, enabling a detailed comparison of the microcrystalline state with the conformation ofsingle crystals and the protein in solution; the consistency of backbone conformation in these threepreparations is the best among proteins studied so far. Signal intensities and line widths vary as a functionof amino acid position and temperature. High-resolution spectra are observed near room temperature (280K) and at <180 K, whereas resolution and sensitivity greatly degrade substantially near 210 K; the magnitudeof this effect is greatest among the side chains of residues at the intermolecular interface of the microcrystallattice, which we attribute to intermediate-rate translational diffusion of solvent molecules near the glasstransition. These features of GB1 will enable its use as an excellent model protein not only for SSNMRmethods development but also for fundamental studies of protein thermodynamics in the solid state.
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