Major curlin subunit (CsgA) (CsgA)

CsgA (major curlin subunit) is the primary structural component of curli, functional amyloid fibers produced on the surface of gram-negative bacteria, particularly *Escherichia coli*[1][2]. Upon secretion through the outer membrane CsgG–CsgE–CsgF complex, CsgA monomers are nucleated by the minor subunit CsgB and assemble into a non-centrosymmetric beta-helical fibril architecture stabilized by hydrogen bonding between five amyloidogenic repeats[1][3]. These curli fibers are integral to bacterial biofilm formation, enabling cell adhesion, surface colonization, and host invasion[2][3]. While CsgA itself is not a therapeutic target in the traditional sense, understanding its structure and assembly mechanisms provides insights relevant to preventing biofilm-associated infections and potentially developing novel anti-biofilm strategies. Additionally, CsgA serves as a model for studying regulated functional amyloid production, with implications for understanding pathological amyloid diseases in humans[2].

Other names

Curlin major subunitCurli fiber proteinStructural subunit of curli fimbriae

CsgA assembly involves: - Nucleation-precipitation mechanism: Unfolded CsgA subunits in solution are nucleated by CsgB (minor subunit), causing ordered assembly into fibers in the extracellular space - Secretion via Type VIII system: CsgA is secreted through the CsgG–CsgE–CsgF complex (outer membrane pore), where accessory proteins CsgE and CsgF regulate controlled export - Chaperone regulation: CsgC (periplasmic chaperone) and CsgE (secretion chaperone) prevent premature amyloid formation and direct CsgA toward secretion - Electrostatic interactions: CsgA contains 10 acidic amino acids and only 4 basic amino acids, enabling negatively charged surface interactions with positively charged regions of chaperone proteins