receptor-mediated endocytosis

Examples of receptor-mediated endocytosis in the following topics:

• Endocytosis

  • A targeted variation of endocytosis, known as receptor-mediated endocytosis, employs receptor proteins in the plasma membrane that have a specific binding affinity for certain substances .
  • In receptor-mediated endocytosis, as in phagocytosis, clathrin is attached to the cytoplasmic side of the plasma membrane.
  • If uptake of a compound is dependent on receptor-mediated endocytosis and the process is ineffective, the material will not be removed from the tissue fluids or blood.
  • Some human diseases are caused by the failure of receptor-mediated endocytosis.
  • In receptor-mediated endocytosis, uptake of substances by the cell is targeted to a single type of substance that binds to the receptor on the external surface of the cell membrane.

• Animal Viruses

  • When a protein in the viral capsid binds to its receptor on the host cell, the virus may be taken inside the cell via a vesicle during the normal cell process of receptor-mediated endocytosis.
  • An alternative method of cell penetration used by non-enveloped viruses is for capsid proteins to undergo shape changes after binding to the receptor, creating channels in the host cell membrane.
  • Enveloped viruses also have two ways of entering cells after binding to their receptors: receptor-mediated endocytosis and fusion.
  • Many enveloped viruses enter the cell by receptor-mediated endocytosis in a fashion similar to some non-enveloped viruses.

• Virus Attachment and Genome Entry

  • Attachment is a specific binding between viral capsid proteins and specific receptors on the host cellular surface.
  • Attachment is a specific binding between viral capsid proteins and specific receptors on the host cellular surface.
  • This is because its surface protein, gp120, specifically interacts with the CD4 molecule, a chemokine receptor, which is most commonly found on the surface of CD4+ T-Cells.
  • Attachment to the receptor can induce the viral envelope protein to undergo changes that results in the fusion of viral and cellular membranes, or changes of non-enveloped virus surface proteins that allow the virus to enter.
  • Penetration follows attachment: Virions enter the host cell through receptor-mediated endocytosis or membrane fusion.

• Viral Identification

  • If the cell has the appropriate receptor on its surface, these viruses sometimes enter the cell by direct fusion with the cell membrane (e.g., herpesviruses) or, more usually, by receptor-mediated endocytosis.

• Diphtheria

  • This signals the cell to internalize the toxin within an endosome via receptor-mediated endocytosis.

• Plant Viruses

  • As plant viruses have a cell wall to protect their cells, their viruses do not use receptor-mediated endocytosis to enter host cells as is seen with animal viruses.

• General Features of Virus Replication

  • Attachment is a specific binding between viral capsid proteins and specific receptors on the host cellular surface.
  • Its surface protein, gp120, specifically interacts only with the CD4 molecule – a chemokine receptor – which is most commonly found on the surface of CD4+ T-Cells.
  • Attachment to the receptor can fore the viral envelope protein to undergo either changes that result in the fusion of viral and cellular membranes, or changes of non-enveloped virus surface proteins that allow the virus to enter.
  • Virions enter the host cell through receptor-mediated endocytosis or membrane fusion.
  • Following the structure-mediated self-assembly of the virus particles, some modification of the proteins often occurs.

• Components of Plasma Membranes

  • The plasma membrane protects the cell from its external environment, mediates cellular transport, and transmits cellular signals.
  • Endocytosis: transports large molecules (or even whole cells) by engulfing them
  • These proteins can be receptors, which work as receivers of extracellular inputs and as activators of intracellular processes, or markers, which allow cells to recognize each other.
  • Membrane receptors provide extracellular attachment sites for effectors like hormones and growth factors, which then trigger intracellular responses.
  • Some viruses, such as Human Immunodeficiency Virus (HIV), can hijack these receptors to gain entry into the cells, causing infections.

• Blocking of Hormone Receptors

  • A receptor antagonist does not provoke a biological response upon receptor binding, but limits or dampens agonist-mediated responses.
  • A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses.
  • Antagonists mediate their effects by binding to the active site or to allosteric sites on receptors, or they may interact at unique binding sites not normally involved in the biological regulation of the receptor's activity.
  • Binding to the active site on the receptor regulates receptor activation directly.
  • The current accepted definition of receptor antagonist is based on the receptor occupancy model.

• Types of Receptors

  • There are two types of receptors: internal receptors and cell-surface receptors.
  • Once inside the cell, many of these molecules bind to proteins that act as regulators of mRNA synthesis to mediate gene expression.
  • There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
  • Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.
  • An example of this type of enzyme-linked receptor is the tyrosine kinase receptor.