integral protein

(noun)

a protein molecule (or assembly of proteins) that is permanently attached to the biological membrane

Related Terms

Examples of integral protein in the following topics:

  • Facilitated transport

    • The substances are then passed to specific integral proteins that facilitate their passage.
    • Some of these integral proteins are collections of beta-pleated sheets that form a channel through the phospholipid bilayer.
    • The integral proteins involved in facilitated transport are collectively referred to as transport proteins; they function as either channels for the material or carriers.
    • Another type of protein embedded in the plasma membrane is a carrier protein.
    • Channel proteins transport much more quickly than do carrier proteins.

  • Two-Hybrid Analysis

    • The yeast two-hybrid screening system is an effective and quick tool for the in vivo study of protein–protein interaction both in prokaryotes and eukaryotes.
    • It is therefore impossible to use them to study the protein–protein interactions between insoluble integral membrane proteins.
    • In the split-ubiquitin system, two integral membrane proteins to be studied are fused to two different ubiquitin moieties: a C-terminal ubiquitin moiety ("Cub", residues 35–76) and an N-terminal ubiquitin moiety ("Nub", residues 1–34).
    • These fused proteins are called the bait and prey, respectively.
    • In addition to being fused to an integral membrane protein, the Cub moiety is also fused to a transcription factor (TF) that can be cleaved off by ubiquitin specific proteases.

  • Fluid Mosaic Model

    • For example, myelin contains 18% protein and 76% lipid.
    • Integral proteins (some specialized types are called integrins) are, as their name suggests, integrated completely into the membrane structure, and their hydrophobic membrane-spanning regions interact with the hydrophobic region of the the phospholipid bilayer .
    • Single-pass integral membrane proteins usually have a hydrophobic transmembrane segment that consists of 20–25 amino acids.
    • Some complex proteins are composed of up to 12 segments of a single protein, which are extensively folded and embedded in the membrane.
    • This arrangement of regions of the protein tends to orient the protein alongside the phospholipids, with the hydrophobic region of the protein adjacent to the tails of the phospholipids and the hydrophilic region or regions of the protein protruding from the membrane and in contact with the cytosol or extracellular fluid.

  • Binding Initiates a Signaling Pathway

    • Cell-surface receptors, also known as transmembrane receptors, are membrane-anchored (integral) proteins that bind to external ligand molecules.
    • G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein.
    • All G-protein-linked receptors have seven transmembrane domains, but each receptor has its own specific extracellular domain and G-protein-binding site.
    • In a signaling pathway, second messengers, enzymes, and activated proteins interact with specific proteins, which are in turn activated in a chain reaction that eventually leads to a change in the cell's environment.
    • Another complicating element is signal integration of the pathways in which signals from two or more different cell-surface receptors merge to activate the same response in the cell.

  • Types of Receptors

    • Cell-surface receptors, also known as transmembrane receptors, are cell surface, membrane-anchored, or integral proteins that bind to external ligand molecules.
    • G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein.
    • Once the G-protein binds to the receptor, the resultant shape change activates the G-protein, which releases GDP and picks up GTP.
    • One or both of these G-protein fragments may be able to activate other proteins as a result.
    • Heterotrimeric G proteins have three subunits: α, β, and γ.

  • Adherens Junctions

    • Anchor proteins, found inside each cell. 
    • These are transmembrane adhesion proteins, whose main portions are located in the extracellular space.
    • This means that the functional as well as morphological integrity of the adherens junctions are calcium dependent.
    • Principal interactions of structural proteins at cadherin-based adherens junction.
    • Actin filaments are associated with adherens junctions in addition to several other actin-binding proteins.

  • Replicative Cycle of HIV

    • HIV replication depends on a complex, coordinated series of events where the virus integrates into the DNA of host cells.
    • This integrated viral DNA may then lie dormant, in the latent stage of HIV infection.
    • During viral replication, the integrated DNA provirus is transcribed into mRNA, which is then spliced into smaller pieces.
    • At this stage, the structural proteins Gag and Env are produced from the full-length mRNA.
    • Steps in the HIV Replication Cycle: Fusion of the HIV cell to the host cell surface.Cell Entry, HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell.Viral DNA is formed by reverse transcription.Viral DNA is transported across the nucleus and integrates into the host DNA.New viral RNA is used as genomic RNA to make viral proteins.New viral RNA and proteins move to cell surface and a new, immature, HIV virus forms.Virus maturation and protease release of individual HIV proteins.

  • Double-Stranded RNA Viruses: Retroviruses

    • Retroviruses are viruses that are able to reverse transcribe their RNA genome into DNA, which is then integrated into a host genome.
    • A special variant of retroviruses are endogenous retroviruses, which are integrated into the genome of the host and inherited across generations.
    • In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein.
    • So, the information contained in a retroviral gene is used to generate the corresponding protein via the sequence: RNA → DNA → RNA → protein.
    • This diagram depicts the viral life cycle of HIV, from infection, integration into a host genome, reconstruction, and formation of new viral particles.

  • Retroviruses and Hepadnavirus

    • Instead of using the RNA for templates of proteins, they use DNA to create the templates, which is spliced into the host genome using integrase.
    • A special variant of retroviruses are endogenous retroviruses , which are integrated into the genome of the host and inherited across generations.
    • In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein.
    • So, the information contained in a retroviral gene is used to generate the corresponding protein via the sequence: RNA → DNA → RNA → protein.
    • This extends the fundamental process identified by Francis Crick, in which the sequence is: DNA → RNA → protein.

  • Scarlet Fever

    • It is carried by the bacteriophage T12, which integrates into the Streptococcal genome, from where the toxin is transcribed.
    • The phage itself integrates into a serine tRNA gene on the chromosome.
    • It is 753 base pairs in length and encodes a 29.244 kiloDalton (kDa) protein.
    • The protein contains a putative 30 amino acid signal peptide.
    • Removal of the signal sequence gives a predicted molecular weight of 25.787 (kDa) for the secreted protein.