Chemical Shifts of Artificial Monomers Used to Construct Heterogeneous-Backbone Protein Mimetics in Random Coil and Folded States.

The construction of protein-sized synthetic chains that blend natural amino acids with artificial monomers to create so-called heterogeneous-backbones is a powerful approach to generate complex folds and functions from bio-inspired agents. A variety of techniques from structural biology commonly used to study natural proteins have been adapted to investigate folding in these entities. In NMR characterization of proteins, proton chemical shift is a straightforward to acquire, information-rich metric that bears directly on a variety of properties related to folding. Leveraging chemical shift to gain insight into folding requires a set of reference chemical shift values corresponding to each building block type (i.e., the 20 canonical amino acids in the case of natural proteins) in a random coil state and knowledge of systematic changes in chemical shift associated with particular folded conformations. Although well documented for natural proteins, these issues remain unexplored in the context of protein mimetics. Here, we report random coil chemical shift values for a library of artificial amino acid monomers frequently used to construct heterogeneous-backbone protein analogues as well as a spectroscopic signature associated with one monomer class, ß3-residues bearing proteinogenic side chains, adopting a helical folded conformation. Collectively, these results will facilitate the continued utilization of NMR for the study of structure and dynamics in protein-like artificial backbones.

Thermal stability and structure of glyceraldehyde-3-phosphate dehydrogenase from the coral Acropora millepora.

Corals are vulnerable to increasing ocean temperatures. It is known that elevated temperatures lead to the breakdown of an essential mutualistic relationship with photosynthetic algae. The molecular mechanisms of this temperature-dependent loss of symbiosis are less well understood. Here, the thermal stability of a critical metabolic enzyme, glyceraldehyde-3-phosphate dehydrogenase, from the stony coral Acropora millepora was found to increase significantly in the presence of its cofactor NAD+. Determination of the structure of the cofactor-enzyme complex (PDB ID 6PX2) revealed variable NAD+ occupancy across the four monomers of the tetrameric enzyme. The structure of the fully occupied monomers was compared to those with partial cofactor occupancy, identifying regions of difference that may account for the increased thermal stability.