Jamming in globular protein cores

Globular proteins rely on a core of hydrophobic amino acids for thermodynamic stability. It’s been known since the dawn of x-ray crystallography that these structures are densely packed, but our recent work has shown that crystal structures resemble jammed packings of hard particles shaped like amino acids. Interestingly, cryogenic (~77 K) crystal structures resemble packings prepared with athermal protocols, but structures resolved at room temperature by NMR spectroscopy resemble denser packings formed by thermal protocols like the one shown here. We conjecture that NMR structures in aqueous, room-temperature solutions allow core amino acids to find denser configurations.