Thursday, November 5, 2009

protien traffic- cel biology- cell transport-btech biotechnology

After protein is produced, dense traffic continues within the cell. Protein is either released from the cell by special transporters, carried to the place in the body where it will be used, or left in the golgi apparatus to be stored and packed until it is needed. This is the reason for the constant protein traffic within the cell

protein traffic that happens when newly produced proteins change their place in the cell. Because some of these proteins begin to be used immediately within the cell, they must be carried to the place where they are to be used; others are sent to a protein storage area of the cell for later usage. Proteins that will be used outside are removed from the cell under the supervision of the cell membrane. In the meantime, proteins that enter the cell from outside, again under the supervision of the membrane, form an important part of this dense protein traffic. In short, within the tiny parameters of a cell there is an incredible amount of activity. Even rush hour traffic in a large city where millions of people live is really at a standstill compared to the dynamism in a cell. Moreover, this dense activity is carried on by our proteins that are about one millionth of a millimeter in size, that inhabit our cells that are one hundredth of a millimeter in size.
wild type strains. In addition, we found that under nitrogen
starvation conditions, when autophagy is triggered, this mutant
Intracellular vesicle traffic in all eukaryotic cells, from yeast to
human, is crucial for normal cell function. Transport of proteins
within the extensive network of membrane-bound compartments
is highly regulated to ensure the specificity and efficiency of
cargo delivery. Considerable progress has been made towards
understanding the molecular basis of membrane traffic. This led
to the identification of a number of traffic pathways and to the
discovery of many of the proteins components that facilitate and
regulate vesicle biogenesis, targeting, and membrane fusion of
the vesicle with its appropriate target organelle. However, the
precise molecular mechanisms that facilitate and regulate these
processes remain unclear. Identification and characterization
of the various regulatory factors that take part in intracellular
protein transport is essential for better understanding of this
complex process.
A novel ubiquitin-like protein family involved in multiple
intracellular trafficking processes
Over the past few years we have been studying questions
related to the molecular mechanism of intracellular membrane
transport aiming to disclose and characterize such novel factors.
On the basis of transport activity in a cell-free transport
assay, we have identified two novel soluble transport factors:
a mammalian 16 kD protein, denoted GATE-16, and SBP56,
a protein whose previous function was unknown. We have
found that GATE-16 interacts with components of the membrane
fusion machinery and characterized these interactions. More
recently we have determined the three-dimensional structure of
GATE-16 at 1.8 Å resolution (Fig. 1), and found that it belongs to
a novel ubiquitin-like (UBL) protein family which appears to be
involved in multiple intracellular membrane trafficking events.
Members of this family include light chain-3 (LC3), a subunit
of the neuronal microtubule-associated protein complex, and
GABA receptor-associated protein (GABARAP), thought to
promote clustering of neurotransmitter receptors. We took
advantage of yeast as a model system for studying membrane
trafficking, focusing on the yeast homologue of GATE-16, Aut7p.
To directly examine the role of Aut7p in vivo, we knocked
out the Aut7p gene in S. cerevisiae. The aut7 null mutant is
viable and shows normal growth on YPD medium, but grows
significantly slower on synthetic medium in comparison with
Fig. 1 Surface contours, charge distribution, and sequence conservation
in GATE-16. A, Surface of GATE-16 colored according to the electrostatic
distribution. Regions of basic potential are colored blue; acidic regions
are in red. Conserved basic positions and partially exposed hydrophobic
residues are labeled.
organisation of traffic :
proteins are synthesized by the planned union of hundreds of amino acids. A special section of between 10 and 30 amino acids form a kind of chain that forms the zip code of the protein. In other words, the zip code written on the envelope is composed of numbers and letters, while the zip code in a protein is composed of amino acids. This code is located on one of the ends of the protein or inside it. As a result, every new protein that is synthesized receives instructions as to where it will go inside the cell and how it will go there.

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