Quaternary Structure of the Tryptophan Synthase α-Subunit Homolog BX1 from Zea mays

The manuscript describes the use of chemical cross-linking/mass spectrometry and mutagenesis to investigate the dimeric interface of the tryptophan synthase α-subunit homolog, BX1. This work indicates that BX1 homodimerization might have served as a mechanism to exclude an interaction with the tryptophan synthase β-subunit, TrpB, at an early time in evolution, thereby eliminating cross-talk between primary and secondary metabolism. This work would be of interest to mass spectrometrists and structural biologist as it presents a workflow to determine the physiological protein-protein interactions within crystal structures using chemical cross-linking/mass spectrometry and mutagenesis as complementary structural biology techniques, thereby eliminating ambiguity and potential mis-assignments due to the presence of additional (artificial) protein contacts formed during the crystallization process.