Lecture 12 - Intracellular transport (pt 2)

what part of the Golgi is the least interconnected?

cis Golgi network

what part of Golgi is the most interconnected?

trans Golgi network

what does the retrieval pathway use?

COPI-coated vesicles

how does the retrieval retrograde transport work?

vesicles from vesicular tubular clusters and the Golgi go to the ER

what are the two things vesicles contain before they go through the retrieval pathway?

• escaped soluble resident proteins

• proteins involved in vesicle budding from ER

how does the retrieval pathway work?

• soluble ER resident protein gets into lumen by accidental diffusion

• KDEL receptor protein binds to it and takes it back to the ER

• KDEL cycles between ER and Golgi

what are the two possible retrieval mechanisms?

• different transport rates

• proteins retained in resident compartment (functions in same compartment form large complexes which prevents packaging into transport vesicles

how does the vesicular transport model work?

• COP!-coated transport vesicles with cargo move forward from one cisternae to another

• COPI return escaped resident ER proteins and Golgi enzymes

which model could move more rapidly?

model 1/vesicular transport model

how does the cisternal maturation model work?

• cisternae moves through golgi apparatus

• vesicular tubular clusters from ER and fusion turns it into cis golgi network

• 1 citerna becomes the next

• existing ones move to the trans Golgi network

• retrieval/retrograde transport by COPI vesicles moves Golgi enzymes and ER resident proteins back

what is the main difference between the two models?

transport vesicles move proteins in the forward (cis to trans) direction

which model could move more slowly?

model 2/cisternal maturation model

high KDEL affinity

vestibular tubular clusters

low KDEL affinity

ER

what is the KDEL affinity change regulated by?

v-type ATPases H+ which changes the pH

• acidic = binding

• neutral = release

how does vesicular transport from trans golgi network to lysosome work?

• vesicles transported into late endosome which eventually becomes a lysosome

• cargo is the lysosomal hydrolases that helps digest things and is needed for function and degradation of macromolecules

Acid hydrolases

• synthesized in ER and processed in Golgi

• degrades macromolecules

• active when pH is acidic (5.0)

how is the protein protected?

• hydrolases only work at low pH

• membrane also protects it

Mannose - 6 - phosphate model

• lysosome hydrolases

• N linked oligosaccharides added in ER

• mannose residue phosphorylated = M6P (cis golgi network)

• m6p receptors in trans golgi network package lysosomal hydrolases

• lysosomal hydrolases are released in late endosome