A short review of protein targeting more specifically mitochondrial protein targeting i.e. post-translational translocation

1. Name - Ipsita Sahoo
Reg no- 200705180160
Guided by- Mr. Gagan Kumar Panigrahi
School of Applied Science, CUTM, BBSR
M Sc. 1st year Zoology
Subject- Cell and Molecular Biology
Topic- “Mitochondrial Protein Targeting”
Session- 2020-22

2. Introduction
Overview of Protein targeting
Protein Import Into Mitochondrial Matrix
Protein transport from cytosol to inner mitochondrial
membrane
Protein transport from cytosol to mitochondrial
inter-membrane space
Conclusion
Reference
CONTENTS

3. Introduction
 Protein targeting or protein sorting is a biological mechanism by
which proteins are transported to their appropriate destinations i.e.
within or outside the cell.
 Since the translation of mRNA into protein by a ribosome takes place
within the cytosol, proteins destined for secretion or a
specific organelle must be translocated. This process can occur during
translation, known as co-translational translocation, or after translation
is complete, known as post-translational translocation.

4. Overview of Protein targeting

5. Protein targeting to Mitochondria
 Mitochondrial proteins are synthesized by 80S cytosolic as well as
70S matrix ribosome.
 About 99% of mitochondrial proteins are encoded by nuclear gene
and are synthesized as precursors on cytosolic-ribosomes.
 Proteins synthesized by cytosolic-ribosomes are translocated into
mitochondria post-translationally.
Inter
membra
ne space

6. Requirement of Mitochondrial protein
import
 Mitochondrial protein import requires translocation complexes that
mediate translocation and mitochondrial targeting signal (MTS)
sequences.
a) Translocation Complexes
Two distinct translocation complex are situated in outer and
inner mitochondrial membranes referred to as TOM (Translocase
of the outer membrane) complex and TIM (Translocase of the
inner membrane) complex.
b) Mitochondrial Targeting Signal
• Length about 10-30 amino acid residues.
• Rich in +ve charged basic amino acid
(Arginine and lysine)
N-terminal cleavable
matrix targeting
sequences (Presequences)
• These proteins includes all outer membrane
protein.
Non cleavable internal
targeting sequences

7. Protein Import Into Mitochondrial Matrix
 Most of matrix targeting proteins enter into mt matrix contain N-
terminal cleavable targeting sequences & synthesized by cytosolic 80S.

8. Protein transport from cytosol to inner mt membrane

9. Protein transport from cytosol to mitochondrial
inter-membrane space

10.  Proteins sorted to mitochondrial destinations other than the matrix
usually contain two or more targeting sequences, one of which may
be an N-terminal matrix-targeting Sequence.
 Some mitochondrial proteins destined for the inter-membrane
space or inner membrane are first imported into the matrix and then
redirected; others never enter the matrix but go directly to their final
location.
Conclusion

11. Reference
 Nelson DL (January 2017). Lehninger principles of biochemistry.
Cox, Michael M.,, Lehninger, Albert L. (Seventh ed.). New York,
NY. ISBN 978-1-4641-2611-6. OCLC 986827885.
 Sommer MS, Schleiff E (August 2014). "Protein targeting and
transport as a necessary consequence of increased cellular
complexity". Cold Spring Harbor Perspectives in Biology. 6 (8):
a016055. doi:10.1101/cshperspect.a016055. PMC 4107987. PMID 250
85907.
 Walter P, Ibrahimi I, Blobel G (November 1981). "Translocation of
proteins across the endoplasmic reticulum. I. Signal recognition
protein (SRP) binds to in-vitro-assembled polysomes synthesizing
secretory protein". The Journal of Cell Biology. 91 (2 Pt 1): 545–
50. doi:10.1083/jcb.91.2.545. PMC 2111968. PMID 7309795.
Lodish H, Berk A, Kaiser C, Krieger M, Bretscher A, Ploegh H,
Amon A, Martin K (2008). Molecular Cell Biology (8th ed.). New
York: W.H. Freeman and Company. pp. 591–592. ISBN 978-1-4641-
8339-3.