surfaceprotein

Surface proteins are proteins located on the exterior of cells or viruses, associated with the plasma membrane or viral envelope. They can be integral membrane proteins that span the lipid bilayer, peripheral proteins that interact with the membrane surface, or proteins anchored by lipid moieties such as glycosylphosphatidylinositol. Surface proteins enable interactions with the extracellular environment and are key to signaling, transport, adhesion, and recognition.

In cellular membranes, surface proteins include receptors that initiate signaling upon ligand binding (such as G protein-coupled receptors and receptor tyrosine kinases), channels and transporters that regulate the passage of ions and small molecules, and adhesion molecules that mediate cell–cell or cell–matrix contacts. Enzymes capable of acting at the cell surface, including ectoenzymes, also fall into this category.

In microbes, surface proteins contribute to attachment, invasion, and immune interactions. Bacteria display adhesins and pili that promote adherence to host tissues, while viral surface proteins mediate attachment and entry into host cells. These proteins are common targets for vaccines, therapeutic antibodies, and antiviral or antibacterial drugs.

Study and clinical relevance: Surface proteins are investigated using proteomics, flow cytometry, and labeling techniques that identify exposed proteins. Because they govern host interactions and pathogenic processes, surface proteins are frequent targets for vaccines, monoclonal antibodies, and inhibitors. Mutations or alterations in surface proteins can affect tissue tropism, virulence, immune evasion, and drug susceptibility.