北京大学：《细胞科学 Cell science》课程PPT讲稿（英文版）Synthesis, sorting and translocation of proteins synthesized in biosynthesis pathway and secretory pathway

胞科学 el Science 蔡国

细胞科学 Cell Science （8.4） 蔡国平

7.4 Synthesis, sorting and translocation of proteins synthesized in biosynthesis pathway and secretory pathway 7.4.1 Two types of proteins Except for few nonneuclear-codeded proteins, all proteins begin being synthesized on ribosomes in the cytosol, and further carry out their synthesis and sorting by followed two ways By one way, the proteins are synthesized and sorted bv biosynthesis or secretory pathway, including: secretory proteins enzymes or proteins resident in the lumens of all EMS as well as integral proteins of the membranes of these organelles and the plasma membrane By another way, all other nuclear-encoded proteins are synthesized and released into the cytosol, as described above These proteins remain in the cytosol unless they contain a specific signal sequence that directs them move to the peripheral pi roteins of the inner surface of the plasma membrane, mitochondrion chloroplasts, microbodies, or nucleus and further sorted and located within the membranes or lumens of these organelles

7.4 Synthesis, sorting and translocation of proteins synthesized in biosynthesis pathway and secretory pathway 7.4.1 Two types of proteins: Except for few nonneuclear-codeded proteins, all proteins begin being synthesized on ribosomes in the cytosol, and further carry out their synthesis and sorting by followed two ways: By one way, the proteins are synthesized and sorted by biosynthesis or secretory pathway, including: secretory proteins, enzymes or proteins resident in the lumens of all EMS as well as integral proteins of the membranes of these organelles and the plasma membrane. By another way, all other nuclear-encoded proteins are synthesized and released into the cytosol, as described above. These proteins remain in the cytosol unless they contain a specific signal sequence that directs them move to the peripheral proteins of the inner surface of the plasma membrane, mitochondrion, chloroplasts, microbodies, or nucleus and further sorted and located within the membranes or lumens of these organelles

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7.4.2 Protens synthesized can move or transport between compartments in different ways 1. There are four fundamentally different ways, by which proteins move through the membranes from one compartment into another and even insert into the membranes Gated transport, by which specific macromolecules, even macromolecule assemblies, move between two topological equivalent spaces in continuity through a pore complex, such as NPC (nuclear pore complex) or the channel complex outer membrane of Mit or ChI., although which also allows free diffusion of smaller molecules Transmembrane transport, the membrane-bound protein translocators by which specific proteins, unfolded usually, are directly translocated in snake-like way across the membrane from the cytosol into a space that is topologically distinct. Such as the transportors or translocators in ER membrane (for initial translocation of novel peptide), the membrane of mit or chl

7.4.2 Protens synthesized can move or transport between compartments in different ways 1. There are four fundamentally different ways, by which proteins move through the membranes from one compartment into another and even insert into the membranes: Gated transport, by which specific macromolecules, even macromolecule assemblies, move between two topologically equivalent spaces in continuity through a pore complex, such as NPC (nuclear pore complex) or the channel complex outer membrane of Mit or Chl., although which also allows free diffusion of smaller molecules. Transmembrane transport, the membrane-bound protein translocators by which specific proteins, unfolded usually, are directly translocated in snake-like way across the membrane from the cytosol into a space that is topologically distinct. Such as the transportors or translocators in ER membrane (for initial translocation of novel peptide), the membrane of Mit or Chl

The. vesicle transport, by transport vesicles the proeins as cargo are ferried from one compartment to another one, and the pieces of membrane with integrated proteins are transmitted from one membrane to another The transport vesicles are formed and deassembled recyclelly in continually budding and fusion-fashion Such as the vesicles transports in secretory pathway and biosynthesis pathway as well endocytosis

The vesicle transport, by transport vesicles the proeins as cargo are ferried from one compartment to another one, and the pieces of membrane with integrated proteins are transmitted from one membrane to another. The transport vesicles are formed and deassembled recyclelly in continually budding and fusion-fashion. Such as the vesicles transports in secretory pathway and biosynthesis pathway as well endocytosis

343 34 350 353 sec Figure 8 19 Visualizing membrane traffic with the use of a photographs shown here, two vesicular-tubular carriers (VTCs) lorvnuxr) containing the Anoreseent protein have budded from

There are other different nonconventional mechanisms and precedents for moving prorins directly across membranes A number of proteins, e.g. FGF, IL-1 synthesized on free ribosomes in the cytosol, arrive at the cell surface without ever entering the classical secretory pathway. And as above mentioned the directly transport of some proteins into lysosomes for degration. It is possible that there are some private transport pumps, by which a subset of small specific proteins are transfered specialy across a particular membrane such as the ABC transporter family, e.g. a small yeast peptide the pheromone a-factor is mediated directly across the plasma membrane into outside of cells. There is also other possibility that some proteins with a certain specific sequence may transfer directly across the membranes, such as HIV-1 TAT protein(86 aa) with of specific sequence(48 to 60) contains a cluster of eight basic amino acids within a nine residues of line sequence(-RKKRRQRRR-), is able to translocate efficiently

There are other different nonconventional mechanisms and precedents for moving prorins directly across membranes. A number of proteins, e.g. FGF, IL-1 synthesized on free ribosomes in the cytosol, arrive at the cell surface without ever entering the classical secretory pathway. And as above mentioned the directly transport of some proteins into lysosomes for degration. It is possible that there are some “private” transport pumps, by which a subset of small specific proteins are transfered specialy across a particular membrane, such as the ABC transporter family, e.g. a small yeast peptide, the pheromone a-factor is mediated directly across the plasma membrane into outside of cells. There is also other possibility that some proteins with a certain specific sequence may transfer directly across the membranes, such as HIV-1 TAT protein (86 aa) with of specific sequence (48 to 60) contains a cluster of eight basic amino acids within a nine residues of line sequence (-RKKRRQRRR-), is able to translocate efficiently

through the plasma membrane and to reach the nucleus And some cytosolic proteins may move to extracellular space, e.g. calmodulin, annexin Il etc s The protein transports are very complex and multisteps process. there are a series of other cofactors or associated proteins that are involved in different steps of these processes. Their different roles will be discussed respectively

through the plasma membrane and to reach the nucleus. And some cytosolic proteins may move to extracellular space, e.g. calmodulin, annexin II etc.. * The protein transports are very complex and multisteps process, there are a series of other cofactors or associated proteins that are involved in different steps of these processes. Their different roles will be discussed respectively

2. Signal peptides and signal patch direct proteins to correct cellular address Each of these modes of protein transfer is usually selective quided by sortting signals in the transported proteins that are recognized by complementary receptor proteins in the target organelles. Such as to be recognized by receptor proteins associated with NPC by the translocator in the membrane to be acrossed, by a complementary receptor in the appropriate membrane to be formed to transport vesicles or to be retained in certain organelles

2. Signal pepitides and signal patch direct proteins to correct cellular address Each of these modes of protein transfer is usually selective quided by sortting signals in the transported proteins that are recognized by complementary receptor proteins in the target organelles. Such as to be recognized by receptor proteins associated with NPC, by the translocator in the membrane to be acrossed, by a complementary receptor in the appropriate membrane to be formed to transport vesicles or to be retained in certain organelles