Remodeling of intracellular membrane traffic by Brucella effectors

Project Summary
Most bacterial diseases of public health significance are caused by pathogens with an intracellular lifecycle
that is integral to their virulence. These microorganisms exploit a variety of host cell functions to ensure
their intracellular survival and proliferation, via delivery of effector proteins or toxins that modulate specific
host processes, including intracellular membrane transport by vacuolar pathogens. The Golgi apparatus
plays a central role in the host secretory traffic of cellular components and is targeted by many bacteria for
the purpose of vacuole biogenesis and maintenance or intracellular nutrient acquisition. Little is known,
however, about the bacterial effectors that exploit this essential organelle, nor how pathogens subvert its
functions for pathogenic purposes. Bacteria of the genus Brucella, which cause the global zoonosis
brucellosis, generate a replication-permissive organelle derived from the host endoplasmic reticulum (ER),
the Brucella-containing vacuole (rBCV), which is essential to their pathogenesis. rBCV biogenesis requires
VirB Type IV secretion system (T4SS)-mediated delivery of effector proteins that modulate specific host
secretory functions. We identified several of these effectors, among which BspB targets the conserved
oligomeric Golgi (COG) complex, a master regulator of Golgi-associated vesicular trafficking, to promote
rBCV biogenesis and bacterial replication. Additional T4SS effectors (BspD and BspF) modulate Golgi-
associated trafficking functions, further supporting a previously unsuspected role of the Golgi apparatus in
the Brucella intracellular cycle. Our findings also suggest that T4SS effectors (BspB/RicA and BspF/BspD)
functionally cooperate in their modulation of membrane transport pathways, arguing that Brucella
modulation of Golgi-associated processes results from the integration of multiple effector functions. Here
we will test the hypothesis that Brucella delivers an array of T4SS effector proteins that modulate
membrane transport functions at the Golgi interface to coordinately promote bacterial proliferation. We will
use genetic, cellular and biochemical approaches to first characterize the Golgi transport pathways that
contribute to Brucella proliferation and define the targets and functional network of Golgi-targeting T4SS
effectors. Second, we will determine the molecular modes of action of the Golgi-targeting T4SS effectors
BspB, BspD and BspF. Last, we will define i) how BspB and RicA coordinately modulate ER-Golgi vesicular
transport to promote rBCV biogenesis and ii) how BspF and BspD co-modulate TGN-associated transport
to promote Brucella replication. The successful completion of this project will uncover bacterial effector-
driven mechanisms of modulation of Golgi-associated membrane transport functions and define new
paradigms of effector functions and coordination in bacterial pathogens, broadly impacting the research
areas of microbial pathogenesis, cell biology and innate immunity.

Grant Number: 5R01AI158372-05
NIH Institute/Center: NIH
Principal Investigator: JEAN CELLI