Crystal contacts engineering of aspartyl-tRNA synthetase from Thermus thermophilus: effects on crystallizability.

To understand how surface residues in a protein structure influence crystal growth, packing arrangement and crystal quality, crystal surfaces were modified and crystallizability of seven different mutants investigated. The model was aspartyl-tRNA synthetase-1 from Thermus thermophilus, a homodimer (M(r) 122000) with a subunit of 580 amino acids. Engineering concerned modification of amino acids involved in packing contacts in the orthorhombic lattice (P2(1)2121) of the synthetase. Comparison of the crystallization behaviour of the mutants indicates a correlation between disruption/addition of packing interactions and crystallizability of the mutants: disruption or modification of lattice contacts prevents crystallization or leads to crystals of poor quality. In contrast, addition of potential contacts leads to well-shaped crystals of same space group and cell parameters than wild-type crystals.