Adhesionin

Adhesionin is a term used in biology to describe a protein that mediates adhesion of a cell or organism to a surface, tissue, or another cell. In many sources, adhesionin is used as a synonym for adhesin, a surface-exposed or secreted protein that enables attachment, establishing colonization and often biofilm formation. Adhesionins are found across bacteria, archaea, fungi, and animals, and can be part of larger structures such as pili or fimbriae or exist as single, non-piliated proteins.

Mechanisms and binding properties are diverse. Most adhesionins recognize specific host receptors, such as glycoproteins, collagen, fibronectin, laminin, or glycosaminoglycans, or they bind to abiotic surfaces. Binding is frequently regulated by environmental cues, phase variation, or mechanical forces in the local milieu. Adhesionin function is central to initial colonization, persistence, and sometimes invasion.

Examples span many groups. Bacteria use fimbrial or afimbrial adhesins such as FimH and PapG in Escherichia coli, intimin in pathogenic E. coli strains, and fibronectin-binding proteins in Staphylococcus aureus. Fungal pathogens, including Candida albicans, express Als family adhesins that promote adherence to host tissues. In multicellular organisms, general adhesion molecules include cadherins, integrins, and selectins, which mediate cell–cell and cell–matrix interactions; these are often described as adhesion receptors, but their ligands can be referred to collectively as adhesionins in broader usage.

Significance and applications include roles in infection and tissue colonization, as targets for vaccines or anti-adhesion therapies, and as tools in biotechnology to control cell attachment or surface binding.