Page 42 - Biennial Report 2018-20 Jun 2021

cellular and organismal phenotype through protein coding and non-coding genes. Individuals of
a species harbor genetic variations at coding and non-coding regions of the genome; these
genotypes do not always translate to phenotype differences. Most of the time, this is ascribable
to the silent nature of the genetic variation, but many predicted deleterious variations also do
not express a phenotype. This phenomenon that buffers the variations to maintain constancy of
phenotypes in a species is known as genetic buffering or mutational buffering and they affect
genotype to phenotype maps. While some of the contributors of mutational buffering have been
deciphered, we still do not have a catalog of processes that can affect mutational buffering.
These processes may have a role in the physiological context of an organism. For example,
expression of phenotypes only in a particular tissue type (examples includes diseases having
polyglutamine expansions in proteins, that exhibits toxicity in a cell type specific manner
although the mutant proteins are ubiquitously expressed), or expression of phenotype only at a
particular time-point even if the gene is expressed throughout life (examples includes late onset
protein aggregation that appears only in aged members of a species).

Through this project they are trying to understand the contributors of mutational buffering that
work by altering the intracellular protein folding environment. Their group has devised a method
to measure mutational buffering in the model organism Escherichia coli using a library of mutant
protein whose activity can be monitored in vivo. The proteins being used are either a fluorescent
protein (GFP) or an antibiotic resistance gene that confers resistance of gentamicin (Gm-R). Using
these tools, they are studying the potential of E. coli to buffer mutations in different states. Their
earlier work had deciphered that exogenous changes to cellular milieu by changing osmolyte
concentrations changes mutational buffering. In the current work, they have used strains that
are unable to import certain osmolytes from the growth medium (Proline and Glycine-betaine
imported deleted strain). They show that these strains have large scale changes in metabolism
as the cells rewire pathways and fluxes to fix the defect in import. These metabolic changes
change the capacity of the cells to buffer mutational variations. Isolating the mutants that were
buffered in these strains they showed that the buffered mutants had problems of folding in vitro
and in vivo suggesting that mutational buffering capacity was affecting deleterious mutations
that affect protein folding in vivo; the osmolyte uptake deficient strain of E. coli was able to fold
these proteins more efficiently in vivo. Using metabolomics and transcriptomics they show that
efficient folding in this strain was not routed through the canonical protein-chaperones but by
the small-molecules milieu of the cell that is dictated by the cellular metabolic state. To underline
the generality of this mechanism in E. coli, they evolved E. coli with different osmotic
composition from wild-type K-12 strain of E. coli. They saw that these cells also evolve the
capacity to buffer mutations differently, and this was helped by the metabolites. Their group is
now trying to examine the connection between cellular protein folding and metabolites in
greater detail, focusing on disease causing mutations in mammalian cell lines, and in the model
eukaryote, S. cerevisiae.

BIOMATERIALS FOR THE DELIVERY OF BIOACTIVE SUBSTANCES

Cellular transportation of therapeutics is hampered by several physical and biochemical barriers.
Therefore, a delivery vehicle (carrier / vector) is needed to carry therapeutics across the cell
membrane to combat various diseases effectively. Designing and development of such vectors

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