Golgi complexGolgi complex

László KŐHIDAI, PhD., Assoc. Prof.Department of Genetics, Cell- and

ImmunobiologySemmelweis University

2008

Camillo GolgiCamillo Golgi(1843-1926)(1843-1926)

Nobel prize 1906Nobel prize 1906

StructureStructure

• SacclesSaccles• TubulesTubules• VesiclesVesicles

structural-fumctional unit: structural-fumctional unit: dictyosomedictyosome 4-6 saccles 4-6 saccles

the structure is polarized into sub-compartmentsthe structure is polarized into sub-compartments

cis Golgicis Golgi medial Golgimedial Golgi trans Golgi trans Golgi

cis Golgi network (CGN)cis Golgi network (CGN) trans Golgi network(TGN)trans Golgi network(TGN)

Dictyosomes of the plant cellsDictyosomes of the plant cells

Synthesis of complexSynthesis of complexpolysaccharidespolysaccharidesof the cell wallof the cell wall

(hemicellulose, pectins)(hemicellulose, pectins)

Main functionsMain functions

• transporttransport

• sortingsorting

• transformationtransformation

• membrane wrappingmembrane wrapping

Pulse-chase techniquePulse-chase technique

CGNCGN• the peptides arrive from the ER in vesiclesthe peptides arrive from the ER in vesicles• they are N-glycosilatedthey are N-glycosilated• no sorting in the ERno sorting in the ER

Bidirectional transport of proteins:Bidirectional transport of proteins:

• soluble, soluble, endogenous proteins of the ER endogenous proteins of the ER recycledrecycled in transport vesicles - in transport vesicles - retention signal retention signal is requiredis required

• sorting and transport of sorting and transport of lysosomal enzymeslysosomal enzymes

Sorting and modification of Sorting and modification of lysosomal enzymeslysosomal enzymes

Mannose-6-phosphate (M-6-P) signaling:Mannose-6-phosphate (M-6-P) signaling:

• based on the recognition of lysosomal hydrolasesbased on the recognition of lysosomal hydrolases• recognition of the “recognition of the “signal patchessignal patches” (proper 3D combination” (proper 3D combination of amino acids) is requiredof amino acids) is required• main working enzyme: GlcNAc-phosphotransferasemain working enzyme: GlcNAc-phosphotransferase

Phosphorylation of the mannoses:Phosphorylation of the mannoses:

• promotes the sorting of these enzymespromotes the sorting of these enzymes • prevents the further modificationsprevents the further modifications

Glycosilation in the GolgiGlycosilation in the GolgiModifications on the Modifications on the N-glycosilationN-glycosilation pattern pattern

• cis-Golgicis-Golgi::mannosemannose-type oligosaccharides-type oligosaccharidescomplexcomplex oligosaccharides oligosaccharides

• TGNTGN::substitution withsubstitution with sialic acids sialic acids - negatively charged - negatively charged

O-glycosilation:O-glycosilation:

• takes place mainly in the takes place mainly in the medial- and trans-Golgimedial- and trans-Golgi• sidechains of Ser and Thr are glycosilatedsidechains of Ser and Thr are glycosilated

Other modificationsOther modifications

• glucose-amino-glycane (GAG) chainsglucose-amino-glycane (GAG) chains

• sulphatation (proteoglycanes, Tyr res. of peptides) - TGNsulphatation (proteoglycanes, Tyr res. of peptides) - TGN

• proteolytic modifications - secretion vesicleproteolytic modifications - secretion vesicle

Synthesis of lipids in the GolgiSynthesis of lipids in the Golgi

ceramideceramideglycolipidsglycolipids

sphingomyelinsphingomyelin

Main transport pathways from Main transport pathways from TGNTGN

Main transport pathways from Main transport pathways from TGNTGN

• endosomal-lysosomal compartmentendosomal-lysosomal compartmentvia transport vesicles - via transport vesicles - M-6-P receptorsM-6-P receptors

• surface membrane - secretionsurface membrane - secretionconstitutive secretion constitutive secretion - transports - transports lipids lipids and and peptidepeptidecomponents of the surface membrane andcomponents of the surface membrane andthe extracellular matrixthe extracellular matrix

• exocytosis exocytosis regulated secretionregulated secretion

acid phosphatasetrans Golgi network

osmium reduction

cis-Golgi

unstained

Enzyme content of different compartments in GolgiEnzyme content of different compartments in Golgi

Modifications of secretory Modifications of secretory vesiclesvesicles

• selective aggregation - TGNselective aggregation - TGN

• further modifications and sortingfurther modifications and sorting

inactive precursor - active enzyme or hormoneinactive precursor - active enzyme or hormone

(e.g. preproinsulin - proinsulin - insulin)(e.g. preproinsulin - proinsulin - insulin)

• concentration - loss of waterconcentration - loss of water

• hydratation - e.g. proteoglyganshydratation - e.g. proteoglygans

• uptake some cytoplasmatic substances e.g. histamineuptake some cytoplasmatic substances e.g. histamine

Alternative pathwaysAlternative pathways

• some molecules do not synthesized on the rERsome molecules do not synthesized on the rER (e.g. interleukin 1(e.g. interleukin 1 and 1 and 1 - IL1 - IL1-IL1-IL1, , basic fibroblast growth factor-bFGF) basic fibroblast growth factor-bFGF)

• these molecules transported by ABC-transportersthese molecules transported by ABC-transporters

• other roles of the alternative pathway:other roles of the alternative pathway:- elimination of toxic proteins- elimination of toxic proteins- regulation of protein concentrations in cytosol- regulation of protein concentrations in cytosol

Defects of sorting mechanismDefects of sorting mechanism

lysosomal enzymes do not enter the late endosomes lysosomal enzymes do not enter the late endosomes

BUTBUT

enzymes enter the constitutive secretory pathway and releasedenzymes enter the constitutive secretory pathway and released

I (=inclusion) cell disease:I (=inclusion) cell disease:- - the the M-6-P signal M-6-P signal is not formen on the enzymesis not formen on the enzymes- lysosomal enzymes “- lysosomal enzymes “escapeescape” from the cell” from the cell- deficient intracellular digestion- deficient intracellular digestion- the - the non-digestednon-digested substances form INCLUSIONS substances form INCLUSIONS

Network of membran flow in Network of membran flow in eukaryotic cellseukaryotic cells

Organell-dependent metabolism Organell-dependent metabolism of lipidsof lipids