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RESEARCH INTERESTS
Filamentous fungi are important in a variety of
environmental niches as primary degraders of organic carbon, are widely
used by industry for the production of enzymes and pharmaceuticals and can
be important pathogens of plants and animals. Central to all of these roles is the
ability to grow in a highly polar manner, secrete enzymes and invade
substrates. Proper growth of the
fungal cell requires coordination of nuclear division, cytokinesis, and
deposition of new cell wall material. To better understand fungal growth we
are pursuing multiple projects in Aspergillus
species.
SEPTINS IN ASPERGILLUS NIDULANS. Every cell must have a mechanism for
doubling its contents and correctly partitioning those contents to daughter
cells. The timing of division must
be delayed until genetic and cellular materials have doubled. The plane of division must be specified
so that each cell gets everything needed for growth. In multicellular organisms, divisions
must be coordinated among different cell types and cellular materials must
be transported to the appropriate locations. In highly polar organisms such as
filamentous fungi this coordination and transport often takes place over
relatively large distances.
The septins function as molecular scaffolds and
diffusion barriers, recruiting other proteins to the division site and
maintaining the integrity of compartments.
They also play roles in membrane recycling and cytoskeletal organization. Septins are central to orderly cell
division in fungi and animals. They
also appear to be major determinants of morphology and development, likely
as a result of their roles in organizing division planes and cytoskeletal elements. While a great deal has been learned about
the functions of septins in unicellular yeast, much less is known about
their functions in multicellular organisms.
We are using the model filamentous fungus A. nidulans to investigate the idea that changes in the
organization of septins result in changes in the proteins that are
recruited and tethered on septin scaffolds and ultimately in changes in
cell morphology.
POLAR GROWTH IN ASPERGILLUS FUMIGATUS. Invasive aspergillosis (IA) is the
most frequent infectious cause of death in leukemia and bone marrow
transplant patients, and is now seen more often than invasive candidiasis.
The conidia of Aspergillus fumigatus, the filamentous fungus that is
the most common cause of IA, are ubiquitous in the environment. These small, round spores are frequently
inhaled, but a competent immune system clears them before they cause
disease. In vitro studies have shown that after breaking dormancy,
the reactivated A. fumigatus conidium undergoes a brief period of
isotropic expansion before a germ tube emerges. As is true for all filamentous fungi,
later growth is highly polar occurring exclusively at the tips of hyphae
that develop from germ tubes or at the tips of branches that emerge from
primary hyphae. This highly polar tip growth allows A.
fumigatus to invade blood vessels and tissues resulting in the necrosis
characteristic of IA. We are using microarray profiling, laser microcapture
and deep sequencing to profile genes that are differentially transcribed
and/or asymmetrically localized during polar growth of germ tubes, hyphae
and branches in A. fumigatus.
PROTEIN MANNOSYLATION
IN ASPERGILLUS NIDULANS AND ASPERGILLUS NIGER. Eukaryotic
proteins require proper glycosylation for secretion, stability, and
function, and yet, despite the fact that roughly half of all eukaryotic
proteins are thought to be glycosylated, relatively little is known about
the mechanisms by which glycans affect proteins. Understanding
glycosylation at the molecular level, however, is vital for protein engineering
strategies for biotechnology applications, especially those that depend
upon robust secretion. The lack of mechanistic detail derives at least in
part from the great diversity of glycans and the complexity of
glycosylation pathways. With recent advances in both genomics and glycomics, it is now possible to apply a comprehensive
systems biology approach to understanding complex glycosylation pathways
and their effects on the resulting glycoproteins.
As primary decomposers of plant biomass in the
environment, fungi secrete large quantities of lignocellulosic-degrading
enzymes and, like other secreted proteins, these cellulases
require glycosylation for secretion, stability, and function. There are two
types of glycosylation on fungal proteins, O-linked and N-linked. Though
both types of glycosylation are complex, O-glycosylation appears to be
somewhat simpler than N-glycosylation, with fewer enzymes involved in a
smaller number of processing steps. We are investigating O-glycosylation in
the model A. nidulans and the
industrially important fungus A. niger.
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