Staphylococcal protein A, or SpA, is a type I membrane protein from the bacterium Staphylococcus aureus. It is bound to the cell wall via its C-terminal cell-wall-binding region X. In the N-terminal half of the protein is its IgG-binding domains E, D, A, B, and C. SpA-IgG interactions are important because it may help to unlock details about alpha-helical proteins and their IgG-like receptors such as cytokines and growth factors.
The Z domain of SpA is an engineered analogue if the IgG-binding domain B. Z domain contains three alpha helices which are arranged in an antiparallel three-helix bundle.
In the picture shown above, the Z domain of SpA is colored by chain. Four types of side chains are visible however: lysine (K)=blue, phenylalanine (F)=aqua, leucine (L)=green, and aspartic acid (D)=red. This domain of the protein contains no disulfide bonds and is 72 amino acid residues long.

• Keywords: Three-helical Bundle Structure, Immunoglobulin-Binding Protein, IgG-Binging Protein, Repeat, Transmembrane, Cell Wall, Signal
• View this protein's PDB entry as 2SPZ
• View this protein's SwissProt entry as SPA2_STAAU
• References:
  • M. Tashiro, R. Tejero, D.E. Zimmerman, B. Celda, B. Nilsson, G.T. Montelione
    High Resolution Solution NMR Structure of the Z Domain of Stapphylococcal Protein A.
    J. Mol. Biol. 272:573 (1997)
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  • L. Jendeberg, M. Tashiro, R. Tejero, B.A. Lyons, M. Uhlen, G.T. Montelione, B. Nilsson
    The Mechanism of Binding Staphylococcal Protein A to Immunoglobin G Does Not Involve Helix Unwinding.
    Biochemistry 35:22 (1996)
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  • M. Tashiro, G.T. Montelione
    Structures of Bacterial Immunoglobin-Binding Domains and Their Complexes With Immunoglobulin.
    Curr. Opin. Struct. Biol. 5:471 (1995)
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  • B.A. Lyons, M. Tashiro, L. Cedergren, B. Nilsson, G.T. Montelione
    An Improved Strategy For Determining Resonance Assignments for Isotopically Enriched Proteins and Its Application to an Engineered Domain of Staphylococcal Protein A.
    Biochemistry 32:7839 (1993)
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