Surface protein antigen(SPA) P is an important virulence factor with high conservation that serves a vital function in mediating the adhesion and biofilm formation of Streptococcus mutans(S.mutans). The SPAP linear sequence comprises a leader peptide, N-terminal, A, V, P, and C-terminal regions, and a cell wall-anchoring segment counting up to 1 561 amino acid residues. The SPAP has an amyloid fibrous property and is thus important in the biofilm formation process. SPAP is closely associated with the development of dental caries because of its interaction with host salivary components, matrix proteins, and other microorganisms. The SPAP covalently combines with the cell wall of S.mutans under the influence of sortase. S.mutans also produces a surface protein-releasing enzyme that degrades SPAP and mediates cell release from biofilms. This review describes the structure and the amyloid fibrous property of SPAP with emphases on studies aiming to characterize the effects of SPAP on S.mutans biofilm formation. This review also aims to identify biological characteristic cues in etiology and potential therapeutic applications of dental caries.
