Chlamydia trachomatis Inclusion Membrane Protein CT228 Recruits Elements of the Myosin Phosphatase Pathway to Regulate Release Mechanisms

Chlamydia trachomatis replicates within a membrane-bound compartment termed an inclusion. The inclusion membrane is modified by the insertion of multiple proteins known as Incs. In a yeast two-hybrid screen, an interaction was found between the inclusion membrane protein CT228 and MYPT1, a subunit of myosin phosphatase. MYPT1 was recruited peripherally around the inclusion, whereas the phosphorylated, inactive form was localized to active Src-family kinase-rich microdomains. Phosphorylated myosin light chain 2 (MLC2), myosin light chain kinase (MLCK), myosin IIA, and myosin IIB also colocalized with inactive MYPT1. The role of these proteins was examined in the context of host-cell exit mechanisms (i.e., cell lysis and extrusion of intact inclusions). Inhibition of myosin II or small interfering RNA depletion of myosin IIA, myosin IIB, MLC2, or MLCK reduced chlamydial extrusion, thus favoring lytic events as the primary means of release. These studies provide insights into the regulation of egress mechanisms by C. trachomatis. [Display omitted] •Chlamydia trachomatis CT228 recruits MYPT1 to the inclusion membrane•MYPT1 is in an inactive phosphorylated form in inclusion microdomains•Active MLCK, MLC2, myosin IIA, and myosin IIB are present in these microdomains•The myosin phosphatase pathway controls chlamydial egress mechanisms Chlamydia trachomatis is a bacterial obligate intracellular pathogen that causes several significant diseases in humans. At the end of their intracellular developmental cycle, chlamydiae are released by lysis of the host cell or extrusion of the intact parasitophorous vacuole (inclusion). Here, Hackstadt and colleagues identify a chlamydial protein that recruits myosin phosphatase, a regulatory protein that controls myosin motor activity on the inclusion membrane and thus controls egress mechanisms of chlamydiae.