Signal peptide peptidase A (IPR033854)

Short name: S49_SppA_1

Overlapping homologous superfamilies


Domain relationships


This entry contains signal peptide peptidase A (SppA; protease IV; MEROPS identifier S49.001). SppA is involved in the cleavage of signal peptides after their removal from the precursor proteins by signal peptidases. Site-directed mutagenesis and sequence analysis have shown SppA to be a serine protease. The predicted active site serine for members in this family occurs in a transmembrane domain. Mutagenesis studies also suggest that the catalytic centre comprises a Ser-Lys dyad (both residues absolutely conserved within bacteria, chloroplast and mitochondrial signal peptidase family members) and not the usual Ser-His-Asp catalytic triad found in many serine proteases [PMID: 18824507]. In addition to the carboxyl-terminal protease domain that is conserved in all the S49 family members, the E. coli SppA contains an amino-terminal domain, similar to Arabidopsis thaliana SppA1 peptidase. Others, including sohB peptidase, protein C and archaeal signal peptide peptidase, do not contain the amino-terminal domain. Unusually, the single membrane spanning E. coli SppA carries out catalysis using a Ser-Lys dyad with the serine located in the conserved carboxy-terminal protease domain and the lysine in the non-conserved amino-terminal domain [PMID: 18164727,PMID: 18476724,PMID: 11741964].

GO terms

Biological Process

GO:0006465 signal peptide processing

Molecular Function

GO:0008236 serine-type peptidase activity

Cellular Component

GO:0005887 integral component of plasma membrane

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.