|
r
e s e a r c h.. f o c u s :
Functional
genomics of fungal control of lipid and membrane homeostasis
The
synthesis, maintenance and regulated dynamics of a wide number of
lipids and membranes are crucial to the organization and function
of all eucaryotic cells. Despite their fundamental roles, their
challenging chemistry and complex natures have inhibited broad investigation
of this fundamentally important area of fungal cell biology. In
collaboration with W. Thomas Starmer in our department, we have
undertaken a systematic functional genomics study in S. cerevisiae
of genes that may mediate resistance to plant natural products that
govern the generation of wild species of yeasts in the genus Pichia.
As these natural products are membrane disturbing saponins, we expect
these studies to aid in our further understanding of the cellular
components that play roles in fungal lipid and membrane homeostasis.
More
about functional genomics...
Wild yeasts of the genus Pichia occur on decaying tissues of different
species of cacti found in the Sonoran Desert and throughout the
world. The presence of plant natural products, specifically triterpene
glycosides, occurring at high levels naturally in these plant
tissues creates unique challenges for such fungi to utilize these
valuable niches in such ecosystems. Triterpene glycosides are
a stunningly diverse chemical scaffold that nature has repeatedly
utilized to create a broad array pharmacologically active chemicals
found in a very large number of plant species, including birch
bark, licorice, black cohosh and many others. We have found that
different commonly used wild type strains of budding yeast differ
markedly and specifically in their response to triterpene glycosides
found in certain Sonoran Desert cacti.
A
collection of "knock-out" strains corresponding to most
of the ~6,200 genes of the budding yeast genome is being screened
for genes whose inactivation leads to sensitivity or resistance
to triterpene glycosides. As the identity of the predicted gene
knocked out in each of these several thousand strains is already
known, we can rapidly identify a functional network of genes involved
in cellular responses to the presence of the triterpene glycoside.
We have already identified known genes by this screen whose functions
are associated with lipid and membrane regulation. As might be
expected for such a fundamental but relatively understudied area
of fungal cell biology, we have also identified a wide variety
of previously uncharacterized genes encoding proteins whose cellular
roles remain to be understood. We are assigning such genes the
name LMH for Lipid and Membrane Homeostasis.
Based
on current estimates, we expect to identify roughly 800 genes
in the yeast genome whose activities affect lipids and membranes
either directly or indirectly. While this number appears relatively
high, about a third of all yeast genes encode proteins that may
be predicted to reside in membranes. A sizeable number of additional
proteins are also peripherally associated with membranes. Still
other proteins play known roles in the synthesis of lipids, membrane
components and their precursors. For example, synthesis of the
predominant membrane sterol, ergosterol, begins with acetyl CoA
and requires 19 enzymatic steps; branches of this pathway are
also required to produce dolichol and geranylgeranyl groups which
function in post-translational modification of proteins. Hence,
the large number of genes uncovered by this screen may, in part,
be expected considering the ubiquitous nature of lipid and membrane
function in eucaryotic, and particularly fungal, cells. Ergosterol
is the direct or indirect target of most classes of commonly employed
antifungal drugs, making information on these genes of fundamental
biomedical relevance. Efforts are presently underway through additional
secondary screens and bioinformatic methods to classify functional
subgroups of the LMH genes and further elucidate the cellular
functions of their gene products.
For
more details about my other research, please select from the following:
|
