Two large classes of GTPase switch proteins are used in signal transduction pathways:

1. Heterotrimeric G proteins

2. Monomeric G proteins

TLS Online TPP Program

#Id: 7916

#XL - Q Biochemistry

Energy inputs are needed to Import proteins into mitochondria

Chaperone proteins (Hsp70& Hsp90)

An H+ electrochemical gradient, or proton-motive force

TLS Online TPP Program

#Id: 7915

#XL - Q Biochemistry

Mitochondrial protein import requires: 

Tom proteins (Tom 20/22/70)

General import pore (Tom40)

Tim proteins (Tim23/17)

TLS Online TPP Program

#Id: 7914

#XL - Q Biochemistry

Matrix-targeting sequences

Located at the N-terminus

Usually 20–50 amino acids in length

Rich in hydrophobic amino acids, positively charged basic amino acids (arginine & lysine), and hydroxylated ones (serine and threonine)

Amphipathicity of matrix-targeting sequences is critical to their function

TLS Online TPP Program

#Id: 7913

#XL - Q Biochemistry

Matrix-targeting sequences

sequences for localizing proteins to mitochondria

TLS Online TPP Program

#Id: 7912

#XL - Q Biochemistry

The majority of proteins located in mitochondria are not encoded by mtDNA, they are encoded by genes in the nucleus and are imported into the mitochondria after their synthesis in the cytosol.

TLS Online TPP Program

#Id: 7911

#XL - Q Biochemistry

MCSs also serve as interfaces for the transfer of ions (Ca+2 ) and small molecules (glycerophospholipids) between the ER and mitochondria.