The perturbation of tryptophan fluorescence by phenylalanine to alanine mutations identifies the hydrophobic core in a subset of bacterial Ig-like domains.

Many host-parasite interactions are mediated via surface-exposed proteins containing bacterial immunoglobulin-like (Big) domains. Here, we utilize the spectral properties of a conserved Trp to provide evidence that, along with a Phe, these residues are positioned within the hydrophobic core of a subset of Big_2 domains. The mutation of the Phe to Ala decreases Big_2 domain stability and impairs the ability of LigBCen2 to bind to the host protein, fibronectin.