1. Protein trafficking is the mechanism by which cells transport proteins to appropriate positions through lysosomes and vesicular transport. 2. Lysosomes contain acid hydrolases that digest molecules and organelles, while vesicular transport uses coated vesicles like clathrin-coated vesicles to move proteins between organelles. 3. Vesicle formation is regulated by GTP-binding proteins and adaptor proteins, while vesicle fusion is mediated by interactions between v-SNAREs on vesicles and t-SNAREs on target membranes through a process called the SNARE hypothesis.

1. PROTEIN TRAFFICKING IN
LYSOSOMES AND
VESICULAT TRANSPORT
NAME: Sheryl Bhatnagar
Roll no.: 2047
Course: Botany(h) 3rd yr

2. Contents
• Introduction
• Translocation pathways
• Lysosomes
• Modifications of lysosomal proteins
• Vesicular transport
• Coated vesicles
• Clathrin coated vesicles
• Formation of coated vesicles
• Vesicle fusion

3. Protein trafficking
• Protein trafficking is the mechanism by which a
cell transports proteins to the appropriate
positions in the cell or outside of it.
• Both in prokaryotes and eukaryotes, newly
synthesized proteins must be delivered to a
specific subcellular location or exported from
the cell for correct activity. This phenomenon is
called protein trafficking.
• This delivery process is carried out based on
information contained in the protein itself.
• Correct trafficking is crucial for the cell; errors
can lead to diseases.
• In 1970, Günter Blobel conducted experiments
on the translocation of proteins across
membranes.
• He was awarded the 1999 Nobel Prize for his
findings. He discovered that many proteins have
a signal sequence, that is, a short amino acid
sequence at one end that functions like a postal
code for the target organelle.

4. Translocation Pathways
CO- TRANSLATIONAL PATHWAY POST-TRANSLATIONAL PATHWAY
• Transport occurs while the polypeptide
chain is being synthesized on a
membrane-bound ribosome.
• Signal sequences are bound by signal
recognition particle (SRP) .
• The polypeptide chain is completed in
the cytoplasm before being transported
into the endoplasmic reticulum.
• Signal sequences recognized by
receptors on translocon (not need SRP) .

5. Lysosomes
• Lysosomes are spherical membranous
bags that contain enzymes (Acid
Hydrolases).
• size varies from 0.1–1.2 μm.
• The lysosomal enzyemes are capable of
digesting all varieties of biological
molecules
 Functions:
I. Digestion of worn out or non
functional organelles.
II. Metabolic functions
III. Degradation of nonuseful tissue

6. Some important enzymes found within lysosomes
include:

7. Modifications of Lysosomal Proteins
• The processing of N-linked oligosaccharides of lysosomal proteins differs from that of
plasma membrane and secreted proteins.
• The lysosomal proteins are modified by mannose phosphorylation.
• First, there is addition of N-acetylglucosamine phosphates to specific mannose
residues, and this happens probably while the protein is still in the cis Golgi network.
• After this N-acetylglucosamine group is removed, leaving mannose-6-phosphate
residues on the N-linked oligosaccharide.
• The phosphorylated mannose residues are specifically recognised by a mannose-6-
phosphate receptor in the trans Golgi network, which directs the transport of these
proteins to lysosomes.

8. Vesicular transport
• Proteins from the ER to the Golgi
apparatus and proteins to E.R and from
golgi to cell organelles, for example,
occurs in this way.
• transport intermediates— which may be
small, spherical transport vesicles or
larger, irregularly shaped organelle
fragments—carry proteins from one
compartment to another.

9. Coated vesicles
Role of the coat:
 Components of the membrane
(e.g. receptors) are
concentrated into patches
 Removal of coated surfaces and
formation of vesicles
Types of coated vesicles:
 Clathrin-coated vesicles
 COPI-coated vesicles
 COPII-coated vesicles
Clathrin-coated vesicle:
Golgi – surface mamembrane
transport
COPI- and COPII-coated
vesicles:
rER - Golgi transports

10. Clathrin-coat
Triskelion zikk-zakk and globular structural elements

11. The Formation of coated vesicles
• The formation of coated vesicles is regulated by small GTP-binding
proteins related to Ras and Ran.
• Two families of GTP-binding proteins play roles in transport vesicle
budding: ADP-ribosylation factors (ARFs 1-3 & Sarl) and a large family
of Rab proteins.
• These regulate adaptor proteins that interact directly with a vesicle
coat protein.
• The binding of GTP-binding proteins and adaptor proteins establishes a
"platform" on the membrane for a specific process, such as assembly
and budding of a transport vesicle directed from the transitional ER to
the Golgi or from the trans Golgi network to endosomes and lysosomes.

12. •Individual proteins in the complex (coat proteins, adaptor proteins, and
GTP-binding proteins) may participate in assembly of transport vesicles
directed elsewhere, or in vesicle,but each protein complex is apparently
unique to a particular budding, transport, or fusion pathway.

13. Vesicle Fusion
• The fusion of a transport vesicle with its target involves two types of
events.
• First, the transport vesicle must recognize the correct target
membrane; for example, a vesicle carrying lysosomal enzymes has to
deliver its cargo only to lysosomes.
• Second, the vesicle and target membranes must fuse, deliver- ing the
contents of the vesicle to the target organelle.
• Analysis of the proteins involved in vesicle fusion in these systems led
Rothman and his colleagues to pro- pose a general model, called the
SNARE hypothesis, in which vesicle fusion is mediated by interactions
between specific pairs of transmembrane proteins, called SNAREs, on
the vesicle and target membranes (v-SNAREs and t-SNAREs,
respectively).
• .

14. According to the hypothesis, the formation of complexes between v-
SNAREs on the vesicle and t-SNAREs on the target membranes leads to
membrane fusion

15. Cont.
• SNAREs are required for vesicle fusion with a target membrane and
that SNARE-SNARE pairing provides the energy to bring the two
bilayers sufficiently close to destabilize them and result in fusion.
• However, the docking, tethering, and fusion of transport vesicles to
specific target membranes appears to be mediated by a sequentially
assembled protein complex much like that which led to transport vesicle
budding.
• Members of the Rab family of small GTP-binding proteins play key roles
in this docking of transport vesicles.
• Rab proteins, like the ARF family, participate in many of the vesicle
budding and fusion reactions during vesicular transport.
• More than 60 different Rab proteins have been identified and shown to
function in specific vesicle transport processes.
• They function in many steps of vesicle trafficking, including interacting
with SNAREs to regulate and facilitate the formation of
SNARE/SNARE complexes.