adhesin

An adhesin is a cell surface protein that mediates adherence to a host tissue or to abiotic surfaces. In bacteria, adhesins are often exposed on the cell surface and can be part of pili (fimbriae) at the tip or exist as non-pilus surface proteins, including autotransporters. Adhesins are also found in some viruses, where attachment proteins function to anchor virions to host receptors.

Adhesins recognize specific receptors such as glycan moieties, extracellular matrix components (fibronectin, collagen, laminin), or protein receptors on host cells. This binding determines tissue tropism and is frequently the first step in colonization and infection. Adhesins can be pilus-associated, featuring a distinct tip adhesin, or afimbrial, and include families such as MSCRAMMs in Gram-positive bacteria and various outer membrane proteins in Gram-negative bacteria.

Examples include FimH, the type 1 fimbrial adhesin of Escherichia coli, which binds mannose residues, and PapG, the P-pili adhesin. YadA from Yersinia is another well-known adhesin. In Staphylococcus aureus, MSCRAMMs such as ClfA and FnbA mediate binding to fibrinogen and fibronectin. Adhesin expression is often regulated by environmental conditions and may involve phase variation or regulatory networks; adhesins can also promote biofilm formation.

Clinical relevance: adhesins contribute to virulence by enabling initial attachment and persistence at interfaces with the host. They are targets for vaccines and anti-adhesion therapies designed to block attachment and prevent infection. Research into adhesins helps illuminate mechanisms of colonization and informs strategies to disrupt microbial adhesion.