The spectral and thermodynamic properties of staphylococcal enterotoxin A,E, and variants suggest that structural modifications are important to control their function
A. Cavallin et al., The spectral and thermodynamic properties of staphylococcal enterotoxin A,E, and variants suggest that structural modifications are important to control their function, J BIOL CHEM, 275(3), 2000, pp. 1665-1672
The superantigens staphylococcal enterotoxin A and E (SEA and SEE) can acti
vate a large number of T-cells, SEA and SEE have approximately 80% sequence
identity but show some differences in their biological function. Here, the
two superantigens and analogues were characterized biophysically. SEE was
shown to have a substantially higher thermal stability than SEA. Both SEA a
nd SEE were thermally stabilized by 0.1 mm Zn2+ compared with Zn2+-reduced
conditions achieved using 1 1 mm EDTA or specific replacements that affect
Zn2+ coordination. The higher stability of SEE was only partly caused by th
e T-cell receptor (TCR) binding regions, whereas regions in the vicinity of
the major histocompatibility complex class II binding sites affected the s
tability to a greater extent, SEE exhibited a biphasic denaturation between
pH 5.0-6.5, influenced by residues in the TCR binding regions. Interesting
ly, enzyme-linked immunosorbent assay, isoelectric focusing, and circular d
ichroism analysis indicated that conformational changes had occurred in the
SEA/E chimerical constructs relative to SEA and SEE. Thus, it is proposed
that the Zn2+ binding site is very important for the stability and potency
of SEA and SEE, whereas residues in the TCR binding site have a substantial
influence on the molecular conformation to control specificity and functio
n.