lysosomes and peroxisomes.pdf

8/10/2019 Lysosomes and Peroxisomes.pdf

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Lysosomes and Peroxisomes

M.Nagalingam

PhD Scholar (P-1737)

IVRI, Izatnagar


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Indian Veterinary Research Institute (IVRI), Izatnagar

Introduction

Lysosomes (Gr., lyso=digestive + soma=body)

Lysosomes are dynamic organelles that receive and degrade

macromolecules from the secretory, endocytic, autophagic and

phagocytic membrane-trafficking pathways.

The lysosomal lumen is maintained at an acidic pH (around 5) by

an ATP-driven proton pump in the membrane.

C. de Duve and his coworkers (1963, 1964, 1974) worked in

Belgium and their approach was biochemical one.

Alex Novikoffand his research group (1962, 1964) worked in

United States and their approach was morphological and

cytochemical


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The lysosomes occur in most animal (except mature

erythrocytes) cells

The lysosomes are round vacuolar structures which remain

filled with dense material and are bounded by single unit

membrane.

Their shape and density vary greatly.

Lysosomes are 0.2 to 0.5m in size. Since, size and shape of

lysosomes vary from cell to cell and time to time (i.e.they arepolymorphic), their identification becomes difficult.

Lysosomes


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Classes of proteins :

Soluble lysosomal hydrolases(also referred to as acidhydrolases) 50 known lysosomal hydrolases

Integral lysosomal membrane proteins (LMPs)

~25 LMPslysosomeassociated membrane protein 1 (LAMP1)

LAMP2,

lysosome integral membrane protein 2 (LIMP2; also

known as SCARB2)tetraspanin CD63

Adaptor proteins AP1, AP3


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Trans Golgi Network


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Targeting of lysosomal proteins by phosphorylation of

mannose residues

Phosphate groups to the 6 position of mannose residues

N-acetylglucosamine phosphates to lysosomal proteins from UDP-N-

acetylglucosamine

Recognition by signal patches


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Endocytosis and lysosome formation


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Possible interaction between endocytosis and biogenesis


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Early endosomes

early endosomal antigen 1 (EEA1) and Rab5 are widely

used as markers

Late endosomes vs lysosomes

lack of M6P receptors in lysosomes


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Clathrins

Recycling of M6PRs by endosometoTGN carriers will not require clathrin ,

but requires the retromer subunit sorting nexin 1 (SNX1) and/or SNX2


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Mannose 6 phosphate independent pathway


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Two major degradation routes:

The lysosomal network and

the ubiquitin-proteasome system .

Proteases

Cathepsin family of proteases

serine (A and G),

Cysteine (B, C, F, H, K, L, O, S, V, W, and X), and aspartic

cathepsins (Dand E).

pH:Vacuolar H+-ATPase, a transmembrane multimeric protein

complex

Degradative function


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Lysosomes in phagocytosis and autophagy


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Autophagy in mammalian cells

Chaperone-mediated autophagy,

Microautophagy,

Macroautophagy

mammalian target of rapamycin (mTOR)


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Lysosomal exocytosis

Lysosomal exocytosis plays a major role in important processes

such as immune responses, bone resorption, cell signaling, andplasma membrane repair


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Evasion of lysosome fusion by microbes

Preventi ng lysosome fusi on -Escherichia coli K1

Delayin g phagolysosome biogenesis-Salmonella

enterica and Mycobacterium tuberculosis

Escaping the phagosome-Listeria, Shigella andRickettsia

Legionella pneumophila, Coxiellabrunetti and Brucella

abortus, can reside in an autophagosomal compartment

where they multiply


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Lysosomal storage disorders

Over50 human lysosomal storage conditions have been recognized, and

although individually rare, their combined prevalence is1in 8000 births

Most of these disorders are autosomal recessively inherited such as Niemann-

Pick disease, type C, however a few are X-linked recessively inherited, such as

Fabry disease and Hunter syndrome (MPS II).

Lysosomal storage disorders frequently involve the central nervous system

L l di d


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Tay-Sachs disease was the first lysosomal storagedisorder (LSD) described, in 1881

Gaucher disease was the second, in 1882

The first link between an enzyme deficiency and aLSD (-glucosidase and Pompe disease) waspublished in 1963 by Hers

The successful treatment of a LSD, Gaucherdisease with -glucosidase, became available in theearly 1990s

Pompe became the first disease formallyrecognized as a lysosomal storage disorder.

Ernest GAUCHER(1854-1919)



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Biochemical and Cellular basis of LSDs

Futerman AH & van Meer G (2004) 5:554-565

1 catalytic activity

2 activator

3 misfolding

4 multienzyme complex

5 glycosylation

6 M-6-P targetting

7 other transport steps

8 membrane transporters

9 membrane regulators

L l di d


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Type of defect protein Disease examples Deficient protein

Lysosomal enzymes primarily

Tay-Sachs disease, I-cell

disease,Sphingolipidoses

(e.g., gangliosidosis, Gaucherand Niemann-Pick disease)

Various

Posttranslational modification of

enzymesMultiple sulfatase deficiency Multiple sulfatases

Membrane transport proteins Mucolipidosis type II and IIIAN-acetylglucosamine-1-phosphate

transferase

Enzyme protecting proteins Galactosialidosis Cathepsin A

Soluble nonenzymatic proteinsGM2-AP deficiency, variant

AB, Niemann-Pick disease, type C2GM2-AP, NPC2

Transmembrane proteins

SAP deficiency Sphingolipid activator proteins

Niemann-Pick disease, type C1 NPC1

Salla disease Sialin



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MPS I (Hurler, Hurler-Scheie, Scheie)

MPS II (Hunter)

MPS III (San filipo Types A,B,C and D)MPS IV (Morquio type A and B)

MPS VI (Maroteaux-Lamy)

MPS VII (Sly)MPS IX (Hyaluronidase deficiency)

Multiple Sulfatase deficiency

I - Defective metabolism of glycosaminoglycans

" the mucopolysaccharidoses"


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Aspartylglucosaminuria

Fucosidosis, type I and II

Mannosidosis

Sialidosis, type I and II

II - Defective degradation of glycan

portion of glycoproteins

III - Defective degradation of glycogen

Pompe disease


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Acid sphingomyelinase deficiency (Niemann-Pick A & B)

Fabry disease

Farber disease

Gaucher disease, type I, II and III

GM1 gangliosidosis, type I, II and III

GM2 gangliosidosis (Tay-Sachs type I, II, III and Sandhoff

Krabbe disease

Metachromatic leukodystrophy, type I, II and III

IV - Defective degradation of sphingolipid

components


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V - Defective degradation of polypeptides

Pycnodysostosis

VI - Defective degradation or transport of

cholesterol, cholesterol esters, or other

complex lipids

Neuronal ceroid lipofuscinosis, type I, II, III and IV


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I-cell disease Caused by the deficiency of an enzyme(N-acetyglucosamine

phosphotransferase) Because of the absence of this enzyme,thesecreted enzymes lack the mannose phosphate residues whichis a signal for targeting lysosomal enzymes to lysosomes.

Symptoms:a rare inherited metabolic disorder characterized bycoarse facial features,skeletal abnormalities and mentalretardation .Many cells from these patients contain lysosomesthat are bloated with undegraded materials. back


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Peroxisomes


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C.de Duve and P. Baudhuin (1966) coined the term peroxisome for the

micro-bodies of mammalian systems and studied their structure and

function.

Called them peroxisomes because they generate and destroy H2O2

All animal cells (except erythrocytes) contain peroxisomes.

Peroxisomes are related to specialized peroxisomes called glycosomes in

parasites such as Trypanosomes, and to plant glyoxysomes

Peroxisomes


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~60 known enzymes in the matrix and ~45 documented

integral or peripheral membrane proteins

Peroxisomes are surrounded by a single membrane and they

range in diameter from 0.1 to 1m

They have crystalline and non-crystalline inclusions.


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Assembly of peroxisomes


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Pex3 is an integral

transmembrane

protein

Pexl9 is a

farnesylated protein

found largely in the

cytosol.

Assembly of peroxisomes


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Protein Import C-terminal signal

sequence: SKL(PTS1)

N-terminal signalsequence: RLX5HL

(PTS2)

Proteins involved inimport: peroxins

Import driven byATP hydrolysis

Dont have to beunfolded for import


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Hydrogen peroxide metabolism

Enzymes involved in the degradative oxidation (e.g., -oxidation of very

long chain fatty acids, 2-methyl-branched fatty acids, dicarboxylic acids,

leukotrienes, bile acid intermediates and cholesterol side chains, and both

a-andb-oxidation of 3-methyl-branched chain fatty acids);

The early steps in the synthesis of ether glycero-lipids orplasmalogens;

The formation ofbile acids, dolichol, and cholesterol; and

The catabolism of purines, polyamines, and amino acids, and the

detoxificationof reactive oxygen species such as hydrogen peroxide,superoxide anions, and epoxides. In methylotrophic yeasts, peroxisomes

are also involved in the metabolism of methanol and methyl amines.

Functions


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peroxisomal diseases

Genes mutation

proteinsinvolved

in the

uptakingMachinery

for

transport

Empty peroxisomes

Enzymes

fail to

be

imported

A single peroxisomal

enzyme absence

Defect in a

membrane protein

that transports VLCFAs

ALD: adrenoleukodystrophy ZS: Zellweger syndrome VLCFAs: Very-long-chain fatty acids

ZS

VLCFAs accumulate

in the brain

ALD


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Thank you


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Acknowledgement

Literature from internet


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I di V t i R h I tit t (IVRI) I t

PEROXISOMAL MATRIX PROTEIN IMPORT

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