Abstract
The Legionella pneumophila effector protein RalF functions as a guanine nucleotide exchange factor (GEF) that activates the host small GTPase protein ADP-ribosylation factor (Arf), and recruits this host protein to the vacuoles in which this pathogen resides. GEF activity is conferred by the Sec7 domain located in the N-terminal region of RalF. Structural studies indicate that the C-terminal region of RalF makes contacts with residues in the Sec7 domain important for Arf interactions. Theoretically, the C-terminal region of RalF could prevent nucleotide exchange activity by blocking the ability of Arf to interact with the Sec7 domain. For this reason, the C-terminal region of RalF has been termed a capping domain. Here, the role of the RalF capping domain was investigated by comparing biochemical and effector activities mediated by this domain in both the Legionella RalF protein (LpRalF) and in a RalF ortholog isolated from the unrelated intracellular pathogen Rickettsia prowazekii (RpRalF). These data indicate that both RalF proteins contain a functional Sec7 domain and that the capping domain regulates RalF GEF activity. The capping domain has intrinsic determinants that mediate localization of the RalF protein inside of host cells and confer distinct effector activities. Localization mediated by the capping domain of LpRalF enables the GEF to modulate membrane transport in the secretory pathway, whereas, the capping domain of RpRalF enables this bacterial GEF to modulate actin dynamics occurring near the plasma membrane. Thus, these data reveal that divergence in the function of the C-terminal capping domain alters the in vivo functions of the RalF proteins.
Highlights
The ADP-ribosylation factor (Arf) family of small GTPases plays an important role in regulating transport of membranes and proteins inside of eukaryotic cells [1,2]
Legionella pneumophila and Rickettsia prowazekii are two pathogenic intracellular bacteria, phylogenetically distant and presenting different intracellular lifestyles. Both organisms encode a protein called RalF, which in Legionella has been shown to be an effector protein that functions as a guanine nucleotide exchange factor (GEF) for the Arf family of eukaryotic GTPases
We show that the Sec7 domains in both proteins have a similar enzymatic ability to activate Arf1, the two proteins differ in their effector functions inside mammalian cells
Summary
The Arf family of small GTPases plays an important role in regulating transport of membranes and proteins inside of eukaryotic cells [1,2]. Guanine nucleotide exchange factors (GEFs) function in Arf activation by stimulating the exchange of GDP for GTP [5], and inactivation of Arf functions depends on GTP hydrolysis stimulated by GTPase activating proteins (GAPs) [6]. Proteins that activate Arf contain a highly conserved Sec domain that is sufficient for GEF activity in vitro [5]. The human genome encodes at least 15 different proteins containing a Sec domain. The diversity in the GEFs in relation to the limited number of Arfs is important because GEFs confer spatial regulation of Arf activation and serve as platforms that assist in recruiting other cellular factors involved in Arf-dependent biological processes [7,8,9,10]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
