Dehydration-Induced Space Group Transition Triggers Conformational Changes in Protein Structure

Protein packing within crystal lattices plays a critical role in determining molecular flexibility; therefore, the observed conformation and flexibility of protein side chains can vary depending on the crystal space group. Protein crystal dehydration affects crystal lattice mosaicity, which can either reduce crystal quality or enhance X-ray diffraction intensity. It also often alters the crystal lattice, leading to space group transition. Accordingly, dehydration-induced space group transitions could theoretically offer an alternative when there are experimental limitations obstructing the obtainment of diverse crystal forms. However, this remains underexplored experimentally. Here, a dehydration-induced space group transition was explored to observe different conformations and flexibilities of the protein structure. Xylanase GH11 crystals from Thermoanaerobacterium saccharolyticum (TsaGH11) were air-dehydrated, and their structure at room temperature was determined. Upon dehydration, the space group of the TsaGH11 crystal changed from tetragonal to orthorhombic, affecting the protein–protein interfaces within the crystal lattice. The dehydrated crystal structure of TsaGH11 revealed multiple conformations of residues involved in substrate binding and recognition within the substrate-binding cleft. These diverse molecular conformations and flexibilities provide significant and previously unrevealed structural information for TsaGH11. This approach demonstrates the potential of dehydration-induced space group transitions to reveal diverse protein conformations, offering valuable insights into molecular properties and functions.