Recently, researchers have gathered an great deal of evidence supporting the idea that cell membrane structure plays a key role in cellular function. This research, which is ongoing, has revealed several different ways in which the protein surface can lead to diverse molecular interactions and a domineering effect over cellular function and behavior.
In “The Cell as a Collection of Membrane Protein from the Perspective of Structural Biology,” authors Shah, Hirst, and Raghu discuss current research on membrane proteins and their possible functions within the cell.
Which Membrane Protein Is Incorrectly Matched With Its Function
Which membrane protein is incorrectly matched with its function?
I. Channel proteins- Allow ions and small hydrophilic molecules to pass through the membrane without using energy.
II. Integral proteins- Hold the phospholipids together in the lipid bilayer.
III. Peripheral proteins- Help enzymes carry out metabolic reactions on the inside and outside of the cell.
IV. Receptor proteins- Bind to specific molecules, allowing cells to sense their environment.
Receptor Protein:
Receptor proteins (also sometimes called recognition proteins) are a type of membrane protein that are specifically designed to receive and transmit chemical signals from outside the cell to the inside of a cell. Receptor proteins are most commonly found on the outside surface of a plasma membrane, but can sometimes be located in other cellular compartments.
They serve as receptors for hormones, neurotransmitters, drugs, antibodies and antigen-antibody complexes.
Channel Protein:
Channel proteins are specialized transport proteins that allow hydrophilic molecules and ions to cross the plasma membrane by forming a transmembrane channel or pore.
Channel proteins generate an aqueous pore through which water-soluble molecules and ions can freely pass from one side of the membrane to the other.
Carrier Protein:
Carrier proteins are integral membrane proteins that undergo conformational changes induced by substrate binding in order to transport ligands across biological membranes. Carrier protein is also known as permease or transporter protein.
Carrier protein is thought to have evolved from enzymes because they share many common features: both bind substrates reversibly and undergo conformational changes during catalysis or transport. Most carrier transport ligands down their electrochemical gradient but some work against it, using energy absorbed from ATP hydrolysis
Transport Proteins
Membrane proteins are a common type of protein which function to span the membrane to which they are permanently attached. They exist in integral and peripheral forms. Membrane proteins perform a variety of functions important to the survival of organisms, including transport and cell signaling.
Integral membrane proteins are firmly embedded in the membrane.
Peripheral membrane proteins are only temporarily bound to the lipid bilayer or to integral proteins by a combination of hydrophobic, electrostatic, and/or ionic interactions.
Transportation Proteins:
* Carrier Proteins
* Channel Proteins
Cell-Cell Adhesion Proteins
These cell-cell adhesion proteins are integral membrane proteins that function to attach and hold cells together. The most common type of cell-cell adhesion proteins are cadherins, the most important of which is the E-cadherin protein.
Cadherins have calcium molecules bound to them, and when the extracellular domains of two adjacent cells bind to each other via their cadherins, a calcium bridge forms between them. This interaction causes the cadherins to crosslink with one another, which increases their rigidity and holds them in place.
The idea that these cell-cell adhesion proteins function as anchors between cells is not entirely accurate. While they do help maintain cell shape, they lack the ability to exert enough force on opposing cells to actually pull them together and prevent them from moving apart.
In fact, one way that cancerous stem cells can undergo metastasis is by using proteases to degrade these proteins so that they can break free from their neighbors and spread throughout the body.
The other major class of cell-cell adhesion protein is integrins. These proteins are heterodimeric, composed of an alpha subunit and a beta subunit, which both must be present for the integrin to function correctly. Integ
Signal Transduction Proteins
Signal transduction proteins are a major class of biological molecules that transmit signals from a receptor to the interior of cells. Many signal transduction proteins constitute part of a signaling pathway, which is a chain of sequential reactions that conveys the signal from an initiating molecule (e.g., a hormone) to its final destination (e.g., DNA). The signal is transmitted from one protein to another through protein-protein interactions. Such interactions occur within signal transduction pathways and also between signaling pathways.
Protein-protein interactions play an essential role in many cellular processes, including regulation of gene transcription, metabolism and cell movement. Protein-protein interactions may be either permanent or temporary:
They are permanent when two proteins are covalently bound to form a single protein complex; e.g., two regulatory subunits of a protein kinase may be permanently bound to form an active enzyme.
They are temporary when proteins interact reversibly; e.g., two proteins may bind transiently through weak non-covalent bonding in order to perform some function such as exchanging material or information between them; e.g., in the transfer of electrons between cytochromes during respiration and photosynthesis, or in the transmission of nerve impulses across synapses .
Plasmalemmal Integral Proteins
- Plasmalemmal integral proteins are involved in cell signaling, ion transport, and the passage of polar molecules into and out of the cell. They can be single-pass or multi-pass transmembrane proteins.
- Glycoproteins are composed of a protein core with oligosaccharides covalently attached to the protein; they are found on the outer surface of a membrane.
- Peripheral proteins are associated with hydrophilic regions of other integral membrane proteins rather than being inserted into the lipid bilayer. Some peripheral proteins are attached via a GPI anchor that is covalently bound to the carboxy terminal residue of the protein inside the cell.
- Lipid-anchored proteins are modified by attaching lipids such as fatty acids or prenyl groups to their C termini; these modify residues protrude from the cell surface and participate in signal transduction reactions by binding to other cells or components in the extracellular matrix.
Last Words
When there is a functional problem with one of the membrane proteins, it will likely lead to a cascade of harmful effects on other parts of the cell. What’s more, a deficit in one type of protein can have a cascading effect on others, which means that many can be lost at the same time.
The body will attempt to repair any damaged membrane proteins, and the ones that do not get fixed are denatured and excreted. However, this is only temporary relief to the affected cells because there are still issues with matching specific proteins to their functions. The cell can experience long-term harm if it does not have enough intact membrane proteins operating at optimal levels.
