Periplasmic space

Structure

As shown in the figure to the right, the periplasmic space in gram-negative or diderm bacteria is located between the inner and outer membrane of the cell. The periplasm contains peptidoglycan and the membranes that enclose the periplasmic space contain many integral membrane proteins, which can participate in cell signaling. Furthermore, the periplasm houses motility organelles such as the flagellum, which spans both membranes enclosing the periplasm. The periplasm is described as gel-like due to the high abundance of proteins and peptidoglycan. The periplasm occupies 7% to 40% of the total volume of diderm bacteria, and contains up to 30% of cellular proteins. The structure of the monoderm periplasm differs from that of diderm bacteria as the so-called periplasmic space in monoderm bacteria is not enclosed by two membranes but is rather enclosed by the cytoplasmic membrane and the peptidoglycan layer beneath. For this reason, the monoderm periplasmic space is also referred to as the inner-wall zone (IWZ). The IWZ serves as the first destination of translocation for proteins being transported across the monoderm bacterial cell wall.