Regulation of dynamic polarity switching in bacteria by a Ras-like G-protein and its cognate GAP

Abstract

The rod-shaped cells of the bacterium Myxococcus xanthus move uni-directionally and occasionally undergo reversals during which the leading/lagging polarity axis is inverted. Cellular reversals depend on pole-to-pole relocation of motility proteins that localize to the cell poles between reversals. We show that MglA is a Ras-like G-protein and acts as a nucleotide-dependent molecular switch to regulate motility and that MglB represents a novel GTPase-activating protein (GAP) family and is the cognate GAP of MglA. Between reversals, MglA/GTP is restricted to the leading and MglB to the lagging pole defining the leading/lagging polarity axis. For reversals, the Frz chemosensory system induces the relocation of MglA/GTP to the lagging pole causing an inversion of the leading/lagging polarity axis. MglA/GTP stimulates motility by establishing correct polarity of motility proteins between reversals and reversals by inducing their pole-to-pole relocation. Thus, the function of Ras-like G-proteins and their GAPs in regulating cell polarity is found not only in eukaryotes, but also conserved in bacteria.

The polarity of myxobacterial gliding is regulated by direct interactions between the gliding motors and the Ras homolog MglA

“…MglA has been observed to localize primarily at the cell poles (13,14); however, most of the components in the gliding machinery, including AglR, localize along the whole cell body (8,9,21), creating a spatial dilemma for the interaction between MglA and the motors. We confirmed the observation that cells expressing MglA-GFP showed bright fluorescence spots primarily at the cell poles; however, we also found blurry GFP fluorescence at nonpolar regions along the cell length (Fig.…”

“…MglA plays a central regulatory role in establishing the polar axis for gliding motility. Mutations in mglA cause dramatic changes in the reversal frequency of gliding cells (13,14). We tested whether MglA directly interacts with the gliding motor protein AglR in the absence of the other gliding-associated proteins present in M. xanthus using a bacterial adenylate cyclase two-hybrid (BACTH) assay.…”

“…The Frz chemosensory pathway regulates the reversal frequency and thus the direction of cell movements of both motility systems (12)(13)(14)(15)(16). MglA, a Ras family GTPase, has been identified as the central regulator of cell polarity and the principal responder to Frz pathway signaling (13)(14)(15). It has been reported that MglA is connected to the Frz pathway by the response regulator RomR (17)(18)(19).…”

“…It has been reported that MglA is connected to the Frz pathway by the response regulator RomR (17)(18)(19). Importantly, MglA switches between an active GTP-bound form and an inactive GDP-bound form, which is regulated by MglB, the cognate GTPase-activating protein (GAP) of MglA, providing another layer of regulation (13,14).…”

“…Gliding M. xanthus cells on 1.5% agar plates typically reverse their polarity approximately every 8-12 min (12). The Frz chemosensory pathway regulates the reversal frequency and thus the direction of cell movements of both motility systems (12)(13)(14)(15)(16). MglA, a Ras family GTPase, has been identified as the central regulator of cell polarity and the principal responder to Frz pathway signaling (13)(14)(15).…”