Figure 2. Cell surface structure of Streptococcus pyogenes.

The peptidoglycan cell wall (shown as a arc) surrounds the plasma membrane (shown as the innermost arc). The hyaluronic acid-containing capsule (shown as the outermost arc) covers the cell wall with a gel-like coat. The peptidoglycan layer typically consists of repeating units of N-acetylglucosamine and N-acetylmuramic acid via 1,4 β-glycosidic linkages. Group A polysaccharide antigen contains N-acetylglucosamine and rhamnose. GAPDH binds to the M-protein attached to the pili (shown by the arrow).