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Protein Transport in Mitochondria

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hello this is seher from easy peasy

and the topic we are going to discuss

today is called as

transport of protein into mitochondria

as we know that mitochondria is the

powerhouse of the cell

as it provides energy to each organelle

in the form of atp molecules

so let's take a closer look at the

structure of mitochondria

if we look closely we can see that

mitochondria consist

of two membranes the outer membrane is

rounded in shape as you can see in this picture

picture

in the red color and inner membrane is

in yellow color

and it is not rounded rather they are

making a lot of different kinds of

folding that is called as christie

the space that is present in between the

outer membrane

and the inner membrane is called as

inter membrane

space and matrix is the inner portion of

the mitochondria

visible in blue color they also have

granules and atp

synthase particles because the major

function of mitochondria is to produce

atp mitochondria also contains

ribosome and deoxyribonucleic acid

it means that mitochondria can produce

its own

protein but if we look at the biogenesis

of the mitochondrial protein

we can see that only one percent of the

mitochondrial proteins

are generated inside the mitochondria

and 99

of the proteins are coming from the

cytosol and then they are imported

inside the mitochondria the function of

mitochondrial protein is the energy metabolism

metabolism

metabolism of amino acids lipid heme

and iron transporters of metabolites

protein transport and folding protein

degradation signaling processes

membrane remodeling fusion and fission

involvement in program cells now let's

take a closer look at the membrane

structure of mitochondria

to understand that how the proteins are importing

importing

inside the mitochondria so this is the

mitochondrial part that we are going to

elaborate now

this is the outer membrane of

mitochondria and this is the inner

membrane of mitochondria

it is not straight because they make a

lot of different foldings

called christie mitochondria usually

attach itself

with the endoplasmic reticulum by a domain

domain

called as e-r-m-e-s

the full form of e-r-m-e-s is

endoplasmic reticulum mitochondria

encounter structure this e-r-m-e-s

subunits are really important because

they are required for the maintenance of

mitochondrial morphology mitochondrial

genome maintenance

and assembly of the outer membrane

protein the outer mitochondrial membrane

is also connected with the inner membrane

membrane

by a structure called as m-i-c-o-s

or mycos the full form of m-i-c-o-s

is mitochondrial contact site

and christy organizing system now micros

are required

for the maintenance of typical

mitochondrial ultrastructure

to facilitate the formation of membrane

contact site

and facilitate the formation of crystal

junction okay

now we have a lot of different type of

proteins that are present on the outer membrane

membrane

and the inner membrane of the mitochondria

mitochondria

and these proteins collectively are

called as translocons with the help of

these translucons

the protein enters the mitochondrial membrane

membrane

and reaches its destination part the

process of

importing protein into the mitochondrial membrane

membrane

consists of four steps first step is the

synthesis of that protein

so for that we need a ribosome messenger rna

rna

and protein so this red color is

basically showing that protein is coming

out of this

machinery the second step is the recognition

recognition

recognition of targeting signals by

targeting factors

if this protein needs to target mitochondria

mitochondria

so the targeting signal will be called

as mitochondrial import sequence

and the targeting factors that are going

to attach itself

with this protein is called as hsp 70

and hsp 90. they are basically the chaperones

chaperones

or heat shock proteins that are going to

attach itself with the protein

and will not allow it to transform into

tertiary and

quatery structure the third step is

called as targeting

targeting of this protein to the receptor

receptor

present on that specific membrane this

receptor is a translocon

present on the outer membrane of the

mitochondria the fourth step is called as

translocation or insertion of the protein

protein

once the protein enters the outer

membrane then they will be targeted to

the subcompartment of that mitochondria

by this way we can recognize four sub-compartments

sub-compartments

where a protein can target itself the

first destination is the outer membrane

the second destination is the inter

membrane space

the third can be inner membrane and the

fourth can be matrix

in this picture we can see that protein

have two different type of signals as well

well

one is called as n-terminal pre-sequence

which have these positively charged

amino acids on it

and one is called as internal targeting signal

signal

to elaborate the signals present on mitochondria

mitochondria

we can see this table now to understand

this table

let's start from the right side now this

is the pre-sequence variation

all the pre-sequence proteins targeted

itself to the matrix inner membrane and

intermembrane space

and all of these proteins are using the

same type of translocons

to reach their destination now if the

protein is targeting the metrics

then they will have the empiphatic

structure on the n-terminal side of that protein

protein

and it will be cleaved once it reached

the matrix by the enzyme

called as mitochondrial processing

peptide a

if the protein is targeting the inner membrane

membrane

then they need a hydrophobic part to integrate

integrate

in that membrane structure for that as

you can see in this picture

that they have the pre sequence plus a

hydrophobic region

shown in the yellow box here and this

pre-sequence will be detached

once it reached to its inner membrane

destination the third type of sequence

is going to stay

in the inter membrane space now in the

inter membrane space they don't need the

hydrophobic region as they are not going

to integrate this protein

into any membrane so if they do have this

this

hydrophobic region as you can see in

this picture

it will be cleaved by inner membrane proteases

proteases

the second category we have is called as

non-cleavable signals

of hydrophobic protein now if the protein

protein

doesn't have the pre-sequences then

there is a 90

chance that they are going to integrate

themselves within a membrane

as you can see in this table all these

destinations are in the outer membrane

outer membrane inner membrane and inner membrane

membrane

they are using different type of

translocons that we are going to discuss

in this video

so let's discuss the first signal that

is the beta signal or beta barrel signal

now this protein have two signals one is

called this

term signal and one is called as beta signal

signal

the beta signal is present near the c

terminal of this protein

when the protein comes out it is going

to enter

the outer membrane first by term signal

and then integrate it in the outer membrane

membrane

by the beta signal the second structure

is called as the alpha helical proteins

now they have three variations the first

variation is that the sequence is

present near the n-terminal

that is going to integrate this protein

in the membrane

and it is called as signal anchor sequence

sequence

it can also be present near the c

terminal so it will be called as

c tail anchor or it can present

in the center of this protein and will

be called as

internal signal some proteins have

multi-spanning so it will cross the membrane

membrane

more than once for that we have various

hydrophobic regions

present on that protein and this green portion

portion

will be used to integrate this protein

in the membrane

so this protein is going to enter the membrane

membrane

three times like this pre-sequence like

internal sequence after hydrophobic region

region

now this type of protein is usually

target the inner membrane of that mitochondria

mitochondria

and it has a hydrophobic region plus the

amphipathic molecule

this hydrophobic region is used to

integrate this protein in the inner membrane

membrane

and this pre-sequence like structure

will hang

in the matrix the third type of signal

is called as

internal signal for inter membrane space

now this protein stays in the

intermembrane space

they used a translocon called mia that

we will discuss in

detail in this video and this protein

usually have cysteine molecules

to make disulfide bonds now let's discuss

discuss

each process in detail so this is the

outer membrane and inner membrane of the mitochondria

mitochondria

and the first translocon that we are

going to discuss here

is called as tom complex time complex is

the major protein

that is present on the outer membrane of

the mitochondria

the full form of tom is called as

translocase of the outer mitochondrial membrane

membrane

now let's see the structure of this term complex

complex

term complex consists of central pore

region called as tom40

they have term 22 that is called a

central receptor

term 70 and term 20 is called as

peripheral receptors

term 5 assists with the transfer of

precursor proteins

term 6 stabilizes the tom complex

and time 7 usually assists the time dissociation

dissociation

now let's see how a protein enters from

the tom complex

now tom complex is used to insert the

protein from

cytosol into the inter-membrane space of mitochondria

mitochondria

so this is the protein that needs to

enter this term

complex and this red portion is

basically the sequence

that is going to tell that this protein

needs to enter the mitochondria

now this protein will be attached by

chaperones that are most likely called as

hsp70 and hsp90

these chaperones will not allow this protein

protein

to turn from primary stage to tertiary

or quaternary stage now the pre-sequence

usually get recognized by

tom 20 and the chevrons are recognized

by co-chaperones that are mostly present

on term

22 and term 17. now for example

in this picture the co chaperones that

are going to recognize the chaperones on protein

protein

is called as xdj1 and djp1

now they will recognize these chaperones

and pre-sequence will be recognized by tom

tom

20. by this way they will let this

protein to enter the core complex

by tom40 like this once the protein

enters inside the inter-membrane space

of mitochondria the pre-sequence will be

cleaved by

inner membrane proteases like this now

if this protein's destination is the

inter membrane space

then it is allowed to transfer into

tertiary or quaternary stage like this

if not then it will remain in the

primary stage

and will transfer to its destination by using

using

other translocons that we will discuss

in this video

now let's see how this protein will

convert itself into tertiary and

quaternary stage

now this is the protein that needs to

turn into the tertiary and quaternary stage

stage

for that this protein needs to have

cysteine residues in it

to maintain the primary stage of this protein

protein

small tin complexes called as tim12

tim 9 tim 10 will attach themselves to it

now this protein needs a translucone

that will help it to turn into its functional

functional

tertiary or quaternary stage for that

the translocon that is going to help it

is called as mia complex the full form

of mia complex

is called as mitochondrial inter

membrane space

assembly machinery mia complex have two domains

domains

one is called as mia 40 and one is

called as

erv1 now mia 40 have the properties of oxidoreductase

oxidoreductase

and erv1 have the properties of sulfhydryl

sulfhydryl

oxidase now let's see how mia complex

is going to help this protein to create

disulfide bonds between them

and turn into its functional state now

this is a beautiful picture

showing the whole process how mia

complex is working

now this is the precursor protein that

needs to transfer

inside the inter membrane space as you

can see

in this protein we have a lot of

cysteine residues

that is represented by sh now this

protein is going to pass through the tom complex

complex

when it comes out of the term complex

mia 40 will make bond

with the sulfur atom present on cysteine

amino acid

so mia40 will recognize this protein

initially once the recognition is done

mia 40 will recruit erv1

erv1 is going to oxidize this protein

by making disulfide bonds between them

now once the protein will take its

functional stage

the tiny tim complexes will remove

itself from it

now the erv1 and mia complex

will detach from itself and erv1 is

going to re-oxidize

by transferring the electrons to the

respiratory chain

and will be available for the next

protein that needs to stay inside the

inter membrane space

the next translocon that we are going to

talk about

is called as mim complex the full form

of mim complex

is mitochondrial import complex

the function of this complex is that

they will take

alpha helical proteins and they will

import these proteins

inside the outer membrane of the

mitochondria the second way to

incorporate this alpha helical structure

inside the outer membrane is that this protein

protein

will enter the inter membrane space

through tom

complex and then they will take the help

of mim complex

and then integrate itself inside the

outer membrane of the mitochondria

now this alpha helical structure can be

of single spanning

or can be of multi-spanning now we have

four different type of alpha helical structures

structures

that can incorporate in the outer

membrane of the

mitochondria the first sequence is

called as

n signal anchor sequence as you can see

that the hydrophobic region is present

near the n-terminal

and it is used to incorporate this protein

protein

inside the membrane and the rest of the

protein will stay

inside the cytosol the second type of

sequence is called a sea

tail and curd sequence as you can see in

this type of sequence

the hydrophobic region is present near

the c-terminal

and the n-terminal region of the protein

will hang in the cytosol

internal signal means that the

hydrophobic region of the protein

will be present in the center of that protein

protein

so half of the protein will be hanging

in the cytosol

and half of the protein will be hanging

in the inter membrane space of

mitochondria and the last

is called as multi-transmembrane

segments as it can penetrate the

membrane several times due to the

presence of several hydrophobic region

inside this protein now mim complex can

incorporate these alpha helical

structures inside the membrane by three

different ways

the first way is this mim complex will

take the help of tom

70 and incorporate the protein inside

the outer membrane in some situations

mim complex can incorporate the protein

in the outer membrane

independently and sometimes the mim

complex take the help of sound complex

and incorporate the protein inside the

outer membrane

one of the studies shows that signal

anchor proteins take the help of term 20

and tom 17 proteins and tail anchor

proteins will take help of term 5

term 6 and tons 7 proteins and these are

the real life examples of the proteins

that enter inside the membrane these

proteins are multi-spanning

and these proteins are entering from the

inter membrane

space of the mitochondria the next

translocon that we are going to discuss

right now

is the sound complex sam stands for

sorting and assembly machinery the

function of some

complex is to incorporate beta barrel protein

protein

from inter membrane space into the outer

membrane of the mitochondria

sound complex consists of three domains

psalm 50 is the core domain

from which the beta battle protein will

assemble itself

and then incorporated into the outer membrane

membrane

sam 35 and zen 37 provide

stability to the sam complex and sound

50 have a domain that is going inside

the inter membrane space called as potra

this portrait is basically the receptor

domain that will

recognize the protein from inter

membrane space and then it will

incorporate it into the outer membrane

the full form of

portra is polypeptide transport

associated domain

now let's see how it's going to perform

its function first of all the protein

from the cytosol will pass through the

tom complex

because as we know from the table beta

battle proteins have two domain sequences

sequences

inside that protein the first sequence

is called a stom

signal it means that it will pass

through the tom complex

first and then it has the beta signal

near the c

terminal and then it will use the sam

complex and will incorporate itself in

the outer membrane in the form of a beta barrel

barrel

so as you can see in this picture this

yellowish portion is basically this protein

protein

it is passing through the term complex

into the inter membrane space

here in order to avoid this protein to

turn back into the tertiary and

quaternary state

tim 9 and tim 10 will help it and will

not allow it to fall back on itself

then it will shift itself into the sam complex

complex

and some complex will shift this protein

in the form of a beta barrel

in the outer membrane of mitochondria

this is basically the assembly part

as you can see that the protein is using

the potter domain

and the core complex in order to

assemble itself

and then move itself outwards in the

outer membrane

the secondary function of the sound

complex is the sam complex is basically

playing an important role

in making the e-r-m-e-s complex

and m-i-c-o-s complex so it is basically connecting

connecting

the inner membrane the outer membrane

and endoplasmic reticulum together on

the mitochondria

so it is playing a big part in the

stability of the mitochondria

the next translocon that we are going to

talk about

is called as tim complex now we have two

different types of tim

complex one is called as tim23

and one is called as tim22 they both perform

perform

different functions so we will discuss

them one by one

so right now we are going to discuss the

structure of tim23

the full form of tim complex is

translucase of the inner mitochondrial

membrane 1050 and tim21 is basically the

receptor domain

that will recognize the pre-sequence

coming from the time

tim 23 and tim 17 is going to play a

role of

core domain and allow the protein to pass

pass

through it from inter membrane space

into the matrix

tim23 is connected with a pam complex

the full form of pam is pre-sequence translocase

translocase

associated import motor nam complex is

playing a role

of pulling the protein into the matrix

it is connected

with the chaperone that is mitochondrial hsp70

hsp70

which is using the atp molecule in order

to pull the protein from intermembrane space

space

into the matrix then we have mge1

that is a co-chaperone that is

stabilizing the attachment of

hsp 70 with the pam complex

we also have another core chaperone

called sim 17

that is preventing the hsp 70 from aggregation

aggregation

now let's see how this 10 23 is going to

perform its function

now this is a step-by-step picture for

how the tim23 is going to work

right now there is no protein coming up

this is the outer membrane having the

tom complex

and this is the inner membrane having

the tim 23 complex

right now the pam complex is not

attached to it

and the tim 23 is closed because 10

21 and 50 are just connected with each other

other

when the protein will be recognized and

passed through the tom complex

the pre-sequence of that protein will be

recognized by

tim 50 and tim 21 by this recognition

1050 and tim 21 will move apart and

open the tim23 core now to pull this protein

protein

into the tim complex the membrane

potential will develop

by this sign and it helps the protein

to move from the tim complex now some

more proteins will come

and attach themselves with the stem

complex that is cox

and bc1 cox is basically the cytochrome

c oxidase enzyme and bc1 is the

respiratory chain

complexes three with the attachment of

these proteins

we have two options now if this protein

destination is the inner membrane

then we have these protease called as

mitochondrial processing peptidase

this protein will remove the

pre-sequence part of this protein

and will allow it to integrate itself

into the inner membrane

if not then pam complex will come and

attach itself with the tim

complex pam complex recruit hsp70

and hsp70 is a chaperon that will use

atp molecules and will start pulling

this protein

from the inter membrane space into the matrix

matrix

once all the protein is inside the

matrix this mitochondrial processing peptidase

peptidase

will cut the pre-sequence part and will

leave the protein

now let's see what happened to this

protein when it is inside the matrix

now this is the same type of thing that

is happening in the previous picture

this is the tom complex this is tim23 complex

complex

and the protein is inserted by the

chaperone hsb hsp70

by using the atp molecule now once the

protein is inside the matrix

some of the more enzymes will come and

will modify this protein

the first enzyme that will come and

remove the n-terminal amino acid from

this protein

is called as intermediate cleaving peptidase

peptidase

and the second enzyme that's going to

come and remove some of the nucleotides

from the n-terminal

and that is called as octa-peptide aminopeptidase

aminopeptidase

now this protein will move towards

another chaperone

that is called as hsp60 with the help of hsp10

hsp10

they will help the protein to fall back

into its functional form

the next translocon that we are going to

talk about right now

is called as tim22 the full form of tim

complex is translocase of the inner

mitochondrial membrane

now tim22 have the tim complex that is a

core domain

and it has 1054 and tim 18 that will act as

a receptor domain and will recognize the

protein from the inter membrane space

now let's see how it's going to perform

its function now here as you can see

this is the outer membrane this is the

inner membrane

and this is the cytosol the protein from

the cytosol is attached itself with the chaperones

chaperones

that are hsp 70 or hsp90 and will

recruit inside the inter membrane space

from the tom complex once the protein is

inside the intermembrane space

tim 9 and tim 10 will attach themselves

with it

and will not allow it to fall back on

itself now this protein

will be recognized by tim 54 and tim

18 and will put this protein in the core

domain of tim22

from here the tim22 complex will insert

this protein

in the inner membrane last but not least

the translocon that we are going to talk about

about

is called as auxar complex now oxa

stands for oxidase assembly machinery

the function of auxacomplex is to

incorporate the protein

from the matrix into the inner membrane

as we know that mitochondria have

mitochondrial dna present in the matrix

and it also has some ribosomes so it can produce

produce

one percent of the protein inside the matrix

matrix

this protein if its destination is the

inner membrane

can use this also complex and will

integrate itself into the inner membrane

now this is a good picture showing us

that how the protein

is moving from mitochondrial matrix to

the inner membrane

a protein from the cytosol can integrate

itself into the inner membrane

after penetrating to the matrix as you

can see in this picture

this is the protein recognized by the

tom complex

then moving in the tim complex the hsb70

is pulling it inside the matrix

now here the protease is going to cleave

the pre-sequence

and this protein if it wants to go back

into the inner membrane

can take help of this auxop complex and will

will

integrate itself into the inner membrane

auxil complex is also working on the

other side now this is the ribosome

inside the matrix

and the protein is coming out of it

while it is still attached itself with

the ribosome

the protein's first part will attach

itself with the auxa1

and alxa 1 with the help of mba1

will start integrating this protein into

the inner membrane

thank you very much for watching this

video if you like it please subscribe

this channel

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YouTube Transcript:Protein Transport in Mitochondria

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YouTube Transcript:
Protein Transport in Mitochondria