6.metabolism in fungi

8/17/2019 6.Metabolism in Fungi

1/67

By Assoc.prof.dr.mohd noor abd.wahab


2/67

GluconeogenesisGluconeogenesis


3/67

Synthesis of glucosefrom pyruvate utilizes manyof the same enzymes as Glycolysis.

Occurs incytoplasm (when onlynonsugar C

sourceis supplied.)

*Reversalof Glycolysis process.

Gluconeoenesis


4/67

Three Glycolysis reactions have such a largenegative G∆ that they are essentiallyirreversible.

Hexokinase (or Glucokinase)PhosphofructokinasePyruvate Kinase.

Therefore,these 3 steps ust be bypasse!in Gluconeogenesis. "thers reactions use the

sae en#ye as in Glycolysis.

GluconeogenesisGluconeogenesis


5/67

Gluconeoenesis


6/67

Glucose-6-phosphatase

Fructose-1,6-bisphosphatase

glucose Gluconeogenesis

Pi

H2O

glucose-6-phosphate

Phosphoglucose Isomerase

fructose-6-phosphate

Pi

H2O

fructose-1,6-bisphosphate

Aldolase

glyceraldehyde--phosphate ! dihydro"yaceto#e-phosphate

$riosephosphateIsomerase

%co#ti#ued&


7/67

Hexokinase or Glucokinase (Glycolysis) catalyzes:

glucose + ATP glucose-6-phosphate + ADP

Glucose-6-Phosphatase (Gluconeogenesis)

catalyzes:

glucose-6-phosphate + H! glucose + Pi

H O

OH

H

OHH

OH

CH2OH

H

OH

HH O

OH

H

OHH

OH

CH2OPO32−

H

OH

H

H2O1

6

'

(

2

! Pi

glucose-6-phosphate glucose


Gluconeoenesis


8/67




Pi

H2O

glucose-6-phosphate



Pi

H2O


Aldolase



%co#ti#ued&


9/67

Phospho"ructokinase %Glycolysis& cataly)es*

"ructose-6-P + ATP "ructose-#$6-%isP + ADP

&ructose-#$6-%isphosphatase %Gluco#eoge#esis& cataly)es*

"ructose-#$6-%isP + H! "ructose-6-P + Pi

fructose-6-phosphate fructose-1,6-bisphosphate

Phosphofructo+i#ase→

CH2OPO32−

OH

CH2OH

H

OH H

H HO

O

6

'

(

2

1 CH2OPO32−

OH

CH2OPO32−

H

OH H

H HO

O

6

'

(

2

1

ATP ADP

Pi H2O

← Fructose-1,6-biosphosphatase

Gluconeogenesis


10/67

Glyceraldehyde--phosphateehydroge#ase

Phosphoglycerate i#ase

.#olase

P.P /arbo"y+i#ase

glyceraldehyde--phosphate

0A! ! Pi

0AH ! H!

1,-bisphosphoglycerate

AP

A$P

-phosphoglycerate

Phosphoglycerate utase

2-phosphoglycerate

H2O

phosphoe#olpyruate

/O2 ! GPG$P

o"aloacetate

Pi ! AP

H/O− ! A$P

pyruate

Pyruate /arbo"ylase

Gluconeogenesis


11/67

$ypass of Pyruvate Kinase%

Pyruvate Kinase (last step of Glycolysis) cataly#es%

phosphoenolpyruvate & 'P pyruvate & 'TP

or bypass of the Pyruvate Kinase reaction,

cleavage of * +P bon!s is reuire!.∆ G for cleavage of one +P bon! of 'TP isinsufficient to !rive synthesis ofphosphoenolpyruvate (P-P).

P-P has a higher negative ∆ G of phosphatehy!rolysis than 'TP.

Gluconeoenesis


12/67

'ypass o" Pyruate inase ( enzy*es):

Pyruate ar%oxylase (Gluconeogenesis) catalyzes:

pyruate + H!,- + ATP oxaloacetate + ADP + Pi

PP ar%oxykinase (Gluconeogenesis) catalyzes:

oxaloacetate + GTP PP + GDP + !

C

C

CH2

O O−

OPO32−

C

C

CH3

O O−

O

ATP ADP + Pi C

CH2

C

C

O

O O−

O−

O

HCO3−

GTP GDP

CO2

pyruate o"aloacetate P.P

Pyruate /arbo"ylase P.P /arbo"y+i#ase

Gluconeoenesis


13/67

.hen gluconeogenesis is actie$ oxaloacetate is /ierte/to "or* glucose0 !xaloacetate /epletion hin/ers acetyloA entry into re%s ycle0 The increase in 1acetyl oA2actiates Pyruate ar%oxylase to *ake oxaloacetate0

PyruvateCarboxylase(pyruvate

oxaloactate)is allostericallyactivated byacetyl CoA.

[Oxaloacetate]tends to belimiting forKrebs cycle.


glucose-6-P glucose

Gluco#eoge#esis Glycolysis

pyruatefatty acids

acetyl /oA +eto#e bodies

o"aloacetate citrate

rebs /ycle


14/67

PEP Carboxykinasecatalyzes ATP-dependentoxaloacetate PEP. It is thought to proceed in 2

steps: Oxaloacetate is firstdecarboxylated to yield a pyruvateenolate anion intermediate.

Phosphate transfer from ATP then yields

phosphoenolpyruvate (PEP).

CC

CH2

O O−

OPO32−

C

CH2

C

C

O

O O−

O−O

CO2

C

C

CH2

O O−

O−

GTP GDP

o"aloacetate P.P

P.P /arbo"y+i#ase 3eactio#


15/67

3n the %acterial4 "ungi enzy*e$ATP is Pi /onor instea/ o" GTP0

3n this crystal structure o" Saccharomyces cerevisiae PPar%oxykinase$ pyruate is atthe actie site as an analog o"PP4 oxaloacetate0

A *etal ion such as 5n+ is reuire/ "or the PP

ar%oxykinase reaction$ in a//ition to a 5g+ ion that

%in/s 7ith the nucleoti/e su%strate at the actie site0

5n+ is thought to pro*ote Pi trans"er %y interacting

si*ultaneously 7ith the enolate oxygen ato* an/ an

oxygen ato* o" the ter*inal phosphate o" GTP or ATP0


16/67

hesource of pyruvate and

oxaloacetate for gluconeogenesis during

fasting or carbohydrate starvation is

mainly glycogen.

Some amino acids are catabolized to

pyruvate, oxaloacetate, or precursors of

these.

Glycerol, derived from hydrolysis of

triacylglycerols in fat cells, is also a

significant input to gluconeogenesis.


17/67

Glyceraldehyde--phosphateehydroge#ase

Phosphoglycerate i#ase

.#olase

P.P /arbo"y+i#ase

glyceraldehyde--phosphate

0A! ! Pi

0AH ! H!

1,-bisphosphoglycerate

AP

A$P

-phosphoglycerate

Phosphoglycerate utase

2-phosphoglycerate

H2O

phosphoe#olpyruate

/O2 ! GPG$P

o"aloacetate

Pi ! AP

H/O− ! A$P

pyruate

Pyruate /arbo"ylase

Gluconeogenesis

ummary of

!luconeogenesisPat"#ay$

!luconeogenesis

en%yme names inred.

!lycolysis

en%yme names inblue.


18/67




Pi

H2O

glucose-6-phosphate



Pi H2O


Aldolase



%co#ti#ued&


19/67

Glycolysis 8 Gluconeogenesis are %oth spontaneous0

3" %oth path7ays 7ere si*ultaneously actie in a cell$ it

7oul/ constitute a 9"utile cycle9 that 7oul/ 7aste energy0

Glycolysis:glucose + AD+ + ADP + Pi

pyruate + ADH + ATP

Gluconeogenesis:

pyruate + ADH + ; ATP + GTP

glucose + AD+ + ; ADP + GDP + 6 Pi

0 Gluconeogenesis expen/s ho7 *any =P >

,0 A "utile cycle o" %oth path7ays 7oul/ 7aste ho7 *any

=P per cycle >

&'


20/67

To prevent the waste of a futile cycle,Glycolysis & Gluconeogenesis arereciprocallyregulated.

Local Control includes reciprocal allostericregulation byadenine nucleotides. Phosphofructokinase (Glycolysis) is inhibited by ATP andstimulated by AMP.

Fructose-1,6-bisphosphatase (Gluconeogenesis) is

inhibited by AMP.

fructose-6-phosphate fructose-1,6-bisphosphate

Phosphofructo+i#ase→ CH2OPO3

2−

OH

CH2OH

H

OH H

H HO

O

6

'

(

2

1 CH2OPO32−

OH

CH2OPO32−

H

OH H

H HO

O

6

'

(

2

1

ATP ADP

Pi H2O

← Fructose-1,6-biosphosphatase

Th it ff t fd i l tid


21/67

Theopposite effects of adenine nucleotides on

o Phosphofructokinase (Glycolysis)

o Fructose-1,6-bisphosphatase(Gluconeogenesis)

insures that when cellular ATP is high (AMP wouldthen be low), glucose is not degraded to make ATP.

When ATP is high it is more useful to the cell to storeglucose as glycogen. >>

When ATP is low (AMP would then be high), the celldoes not expend energy in synthesizing glucose.

>>

!luconeogenesis

!lycolysis


22/67

GLOBALGLOBAL

CONTROLCONTROL


23/67

TRANSLOCATION

AND STORAGECOMPOND


24/67

Environment rarely contains favorable

and ideal condition of nutrients for fungalto growth.

Storage of excess nutrients enables

fungi to survive


25/67

STORAGE COMPOND Storage requirements of growth taes place in all

hyphae components

!yphae fragment function as storage

"rotection from mechanism #

thic wall

protective compound

hydrophobic surface

complex structure $starvation%


26/67

STORAGE COMPOND &iffer from those of plants or bacteria but are similar

to those of animals.

The main storage compound are #'

' (ipid

' Glycogen $) * lined polymer of glucose%

' Trehalose $non * reducing disaccharides%

Trehalose, composed of + glucose residue


27/67

L!p!d

' ften seen as globules in fungal cell

' -p to /0 of cytoplasm made up of lipid

' il drop can de seen in most hyphae of old

compartments

' Glycerol is common and important in water

regulation and metabolic activity in fungi


28/67

L!p!d

'Translocation of lipid was bi * directional in the

same hyphae

'(ipid translocated all direction in the 12-$1unctional 2yceluim -nit%

'"art of mechanism for redistributing energy in

the 12-

3 12- 4 integrated hyphae forms an individualistic organisms


29/67

CARBO"#DRATES2ain translocated carbohydrates

' Trehalose' "olyols $ sugar alcohol%

omycetes absence of the characteristic

fungal carbohydrates


30/67

CARBO"#DRATES

T5E!6(SE

' &erived from common sugars taen from the cells

' Eg #'

7 Trehalose 4 + glucose compound

7 2annitol 4 1ructose

' 5eadily interconverted in hyphae

' Trehalose 4 mycelium

' Trehalose 8 arabitol 4 colony margin


31/67

CARBO"#DRATES

T5E!6(SE

' important in resistance against adverse condition 9

cold, heat, dehydration and etc.

' synthesis and degradation highly regulated


32/67

NITROGEN

' stored as protein' abundant at beginning of degradative cycle

' lectin found freely in cytoplasm

' lectin highly conserved nitrogen storage proteins


33/67

TRANSLOCATION O$

STORAGE COMPND


34/67

TRANSLOCATION IN $NGI

There are different mechanisms for nutrient

translocation in fungi #'

7 "assive

7 "assive 8 active uptae

7 6ctive, cytoplasmic

7 6ctive, pressure driven bul flow


35/67

PASSI%E

:ot required extra energy

:utrients taen by hyphae by simple diffusion

as in water phase

;n non' saturated soil filled with air gaps,

hyphae forms bridges and nutrients can spread

via symplastic or apoplastic diffusion

Eg # Glucose taen at hyphae tips and trehalosediffuse down the < = gradient away from hyphae

tips


36/67

PASSI%E & ACTI%E PTA'E

Similar to passive but nutrients taen in excessof local needs

"roduced steep nutrient gradient inside hyphae

5esult faster delivery of nutrients to mycelium

5equires extra energy for the excess uptae


37/67

ACTI%E( C#TOPLASMIC

6ctive movement in cytoplasm either through#

' movements of organelles' peristaltic vacuole system

2echanisms involve compartmentalization of

nutrients followed by peristaltic movements intubular compartment

Storage compound pacaged in vesicles which

moved at hyphae

6ction of cytoseleton significant in movement

of vesicles along hyphae


38/67

ACTI%E( PRESSRE DRI%EN BL'$LO)

;f excess nutrients are taen, it result in a high

osmotic pressure inside hyphae, water will flowthrough cell membrane

This will create high turgor pressure and water

> nutrient will flow inside mycelium with lessresistance

Energy are use for active uptae and overcome

water flow within hyphae

1ormation of fruiting body is the evidence of

bul flow seen as exudation of water droplet at

the surface


39/67

?idirectional transport shown that #'

Organic carbonHOST HYPHAE TIPS

ROOT

M inerals


40/67

BIOSYNTHESI

S OF FUNGI


41/67

)ha* !s b!osyn*h+s!s,

Th+ prod-c*!on ofn++d+d c+-ar

compo-nds( -s-ay

from s!mp+rmo+c-+s

In fungi, the most important

compound to synthesis :

CHITIN


42/67

C"ITIN

long-chain polymer of a N-acetylglucosamine, aderivative of glucose, and is found in many placesthroughout the natural world. It is the main

component of the cell walls of fungi.

modified polysaccharide which containsnitrogen; it is synthesized from units of N-

acetylglucosamine (more precisely, 2-(acetylamino)-2-deoxy-D-glucose).

Linked by β (1-4) bonds.


43/67

The basic unit is derived from fructose-6-phosphate bythe addition of an amine and an acetyl group from the

amino acid glutamine and acetyl CoA, respectively.

The chitin adds rigidity and structural support to thethin cells of the fungus, and gives protection as well.

described as cellulose with one hydroxyl group on eachmonomer substituted with an acetyl amine group.

This allows for increased hydrogen bonding betweenadjacent polymers, giving the chitin-polymer matrix

increased strength.


44/67

C"ITOSANChitosan is a modified carbohydrate polymer/derived from the chitin component.

Chitosan is a linear polysaccharide composed ofrandomly distributed β!"#$lin%ed D&lucosamine

!deacetylated unit$ and 'acetylD&lucosamine

!acetylated unit$(

Poorly or non acetylated form of chitin(


45/67

Chitosan is obtained by removing enoughacetyl groups (CH3-CO) for the moleculeto be soluble in most diluted acids.

This process) called deacetylation(


46/67


47/67


48/67

SYNTHESIS OF CHITIN

*irst combined ith a donor molecule) to pro,ide theener&y re-uired for synthesis(

.TP + 'acetyl&lucosamine .DP'

acetyl&lucosamine + Pi

/econd) .DP'acetyl&lucosamine combine ith poly'acetyl&lucosamine to form .DP + chitin(

!Donor +su&ar unit$ + acceptor donor +!acceptor+ su&ar unit$


49/67


50/67

C"ITIN S#NT"ASE

Exist inzymogen form then converted into functionalenzyme by partial proteolysis with protease enzyme.

In this state, functional enzyme is formed and readily

to work.

Occur in particles, termed ‘chitosomes’.

Small spheroidal bodies, 40-70 nm diameter,surrounded by a shell. (about 7nm thick).


51/67

CONT…

If presence of an activator (proteolytic enzyme) andsubstrateN-acetylglucosamine, chitosome now canformed chitin microfibril by breaking the shell.

As ‘microvesicles’ in hyphal tips. Extracted from members of all the main chitin-containing fungal groups:(i) Allomyces(ii) Mucor(iii)Saccharomyces

(iv)Neurospora(v)Agaricus.


52/67

SECONDARY

METABOLISM IN FUNGI

Rf t id f tbli


53/67

Refers to a wide range of metabolicreactions whose products are not directlyor obviously involved in normal growth.

Features:

Tend to produced at the end of theexponential growth phase in batch culture or

when growth is substrate-limited incontinuous culture


54/67

Produced from common

metabolic intermediates but by

special en0ymatic pathays

encoded by specific &enes

'ot essential for &roth or

normal metabolism


55/67

Important for commercial or environmental

significancePenicillins (from Penicillium chrysogenum)

Griseofulvin (from P.griseofulvum)-antibiotics produced

commercially from fungi

Carotenoid pigments in conidia fungi such as

Neurospora crassa

Gibberellins-plant hormone for horticulture


56/67

Many secondary metabolites have no obvious roles in

the life of the producer organism, and mutated strains

that do not produce this compound often grow as wellas the wild-type strains in culture.

Instead of that,secondary metabolism acts as an

overspill or escape valve,to remove intermediates from

the basic metabolic pathways when growth is

temporarily restricted.


57/67

Th+ Pa*hway andPr+c-rsors of

S+condaryM+*abo!sm


58/67

A few key intermediates of the basic metabolic

pathways provide starting points for the pathways

of secondary metabolism.

The single most important secondary metabolic

pathway is the polyketide pathway.

The precursor is acetyl-Coa which is carboxylatedto form malonyl-Coa,then three or more molecules

of malonyl-Coa condense with acetyl-Coa to form

chains.


59/67

This chains under&o

cycli0ation)then the rin& systems aremodified to &i,e a ide ran&e of

products such as anti biotic

&riseoful,in!treat dermatophyteinfections$

Another important secondary

metabolic pathay of fun&i is the

isoprenoid pathay for the synthesis

of sterols(


60/67

AcetylCoa is the precursor)but three

molecules of this condense to form

me,alonic acid!1C$ hich iscon,erted to a C isoprene unit(

The isoprene units condense head

totail to form chains under&ocycli0ation and further modifications(

The product in this pathay include

mycotoins of *usarium spp(that &roon moist &rain such as T2 toin and

the trichothecenes(


61/67

EXAMPLE OF SECONDARY

METABOLITES

Penicilins

Mycotoxins

Ergot Alkaloids

Aflatoxins

Sporidesmin

Patulin

Roquefort Cheese


62/67

PENICILLINS

Was discovered by Alexander Fleming in 1929 as a metaboliteof Penicillium chrysogenum .

Most active against Gram-positive bacteria. It prevent thecross- linking of peptides during the synthesis ofpeptidoglycan layer in bacteria cell wall making it weak andsusceptible to osmotic lysis.


63/67

MYCOTOXINS

Diverse range of compounds from differentprecursors and pathway.

Cause toxicity when humans ingest them over arelatively long period of time, from lowconcentrations in improperly stored food.

The problem to detect this toxins is it may takeyears before the effect of exposure become evident.

So to avoid this problem we must storage our food inits proper place.


64/67

OTHER TOXINSToxin Representative

fungi

Foodstuff Effects

Aflatoxins Aspergillus flavusand

A. parasiticus

Peanuts,

oilseeds

Nephrotoxic,

Hepatocarninomas

Ergot alkaloids Claviceps purpurea Cereals,

grasses

Nuerotoxic

Fuminosins Fusarium moniliforme Maize Human esophagealcancer

Ochratoxin A Some Aspergillusand

Penicillium spp.

Grain crops Nephrotoxic and kidney

carcinoma

Patulin Penicillium expansum

and Aspergillus

clavatus

Apples Contact edema and

hemorrhage

Sporidesmin Pithomyces chartarum Grass Facial eczema of sheep

and cattle

Sterigmatocysti

n

Aspergillus spp. Grain, Oilseeds Hepatocarcinogen


65/67

STRUCTURE OF SOME TOXINS

Ergotalkaloids

Aflatoxins


66/67

Sporidesmin


67/67

ROQUEFORT CHEESE

Roquefort cheese and other blue-veined cheeses areproduced from goat milk that are inoculated with

the fungus Penicillium roqueforti.

The cheese contain low levels of the mycotoxinroquefortinebut these levels are not considered tobe hazardous.

The end

6.metabolism in fungi

Documents