Structure of staphylococcal enterotoxin C2 at various pH levels

Area of Science:

• Structural biology
• Microbiology
• Biochemistry

Background:

• Staphylococcal enterotoxin C2 (SEC2) functions as both a toxin and a superantigen.
• Understanding the structural basis of SEC2's activity is crucial for its study.

Purpose of the Study:

• To determine the three-dimensional structure of SEC2 at various pH levels.
• To investigate the role and behavior of a zinc-binding motif within SEC2.

Main Methods:

• X-ray crystallography was employed to obtain SEC2 structures from tetragonal and monoclinic crystal forms.
• Molecular replacement and ARP/wARP programs were used for structure determination across different pH conditions (5.0-8.0) and temperatures (100 K and 293 K).

Main Results:

• The three-dimensional structures of SEC2 were resolved at pH 5.0, 5.5, 6.0, 6.5, and 8.0.
• A zinc atom was identified within a D+HExxH zinc-binding motif, suggesting potential catalytic activity, though not yet biologically confirmed.
• Zinc remained coordinated across all tested pH values, with coordination distances decreasing as pH increased, being minimal at pH 8.0.

Conclusions:

• SEC2 maintains its structural integrity and zinc coordination across a range of pH values.
• The identified zinc-binding motif and its behavior suggest potential catalytic functions, warranting further investigation.
• The structural data provides insights into SEC2's stability and potential enzymatic activity, relevant to its role as a superantigen and toxin.