What Is a Membrane Protein?

The proteins contained in biofilms are called membrane proteins, which are the main bearers of biofilm functions. According to the ease of protein separation and the location in the membrane, membrane proteins can be basically divided into three categories: external membrane proteins or peripheral membrane proteins, internal membrane proteins or integral membrane proteins, and lipid-anchored proteins. Membrane proteins include glycoproteins, carrier proteins and enzymes. There are usually some sugars connected to the membrane protein. These sugars are equivalent to transmitting signals into the cell through the molecular structure of the sugar itself.

Membrane Protein

The outer membrane protein is distributed on the inner and outer surface of the membrane, accounting for about 20% to 30% of the membrane protein. It is mainly a water-soluble protein on the inner surface. It is combined with the polar head of the membrane lipid molecule through ionic and hydrogen bonds , Or via

Techniques for studying the structure of membrane proteins include X-ray diffraction,

Expression systems commonly used for recombinant membrane proteins include eukaryotic expression systems, prokaryotic expression systems, and cell-free expression systems developed in recent years. Where

The functions of membrane proteins are multifaceted. Membrane proteins play a very important role in many life activities of the organism, such as cell proliferation and differentiation, energy conversion, signal transduction, and material transport. It is estimated that approximately 60% of drug targets are membrane proteins.

Membrane proteins can act as "carriers" to transport substances into and out of cells. Some membrane proteins are specific receptors for hormones or other chemicals, such as thyroid cells that accept thyroid-stimulating hormone receptors from the pituitary gland. There are various enzymes on the surface of the membrane, so that specific chemical reactions can be performed on the membrane, such as on the endoplasmic reticulum membrane, which can catalyze the synthesis of phospholipids. Cell recognition also depends on proteins on the membrane surface. These proteins are often surface antigens. Surface antigens can bind to specific antibodies. For example, there is a protein antigen HLA on the surface of human cells, which is a dimer with many changes. Different people have different HLA molecules. When an organ is transplanted, the implanted organ is often rejected. This is because the HLA molecules implanted in the cell are not accepted by the recipient.

Many membrane proteins can move freely in the lipid bilayer. This can be achieved by the fusion of human and mouse cells, and then the antibody of one of the cells, such as the antibody of mouse cells, is stained with a fluorescent dye, and then this kind of The fluorescent antibody is placed in the outer medium of the fused cell, and the antibody will bind to the surface antigen of the mouse cell. As a result, there was fluorescence on the surface of mouse cells, but human cells did not have fluorescence because they did not bind to mouse antibodies. This allows the surface antigens of the two cells to be distinguished under a fluorescent microscope. The experimental results show that when cells begin to fuse, the surface antigens of human and mouse cells are distinct, and they are distributed on their own cell surfaces only; but after fusion, the two antigens are gradually evenly distributed on the surface of the fused cells. This experiment shows that the membrane protein is mobile and also proves the fluidity of the membrane. Note, however, that some membrane proteins are immobile or cannot be moved freely.